eventespresso / event-espresso-core

core/data_migration_scripts/EE_Data_Migration_Script_Base.core.php

Indentation +876 added lines, -876 removed lines

@@ -15,880 +15,880 @@
 abstract class EE_Data_Migration_Script_Base extends EE_Data_Migration_Class_Base
 {
 
-    /**
-     * Set by client code to indicate this DMS is being ran as part of a proper migration,
-     * instead of being used to merely setup (or verify) the database structure.
-     * Defaults to TRUE, so client code that's NOT using this DMS as part of a proper migration
-     * should call EE_Data_Migration_Script_Base::set_migrating( FALSE )
-     *
-     * @var boolean
-     */
-    protected $_migrating = true;
-
-    /**
-     * numerically-indexed array where each value is EE_Data_Migration_Script_Stage object
-     *
-     * @var EE_Data_Migration_Script_Stage[] $migration_functions
-     */
-    protected $_migration_stages = array();
-
-    /**
-     * Indicates we've already ran the schema changes that needed to happen BEFORE the data migration
-     *
-     * @var boolean
-     */
-    protected $_schema_changes_before_migration_ran = null;
-
-    /**
-     * Indicates we've already ran the schema changes that needed to happen AFTER the data migration
-     *
-     * @var boolean
-     */
-    protected $_schema_changes_after_migration_ran = null;
-
-    /**
-     * String which describes what's currently happening in this migration
-     *
-     * @var string
-     */
-    protected $_feedback_message;
-
-    /**
-     * Indicates the script's priority. Like wp's add_action and add_filter, lower numbers
-     * correspond to earlier execution
-     *
-     * @var int
-     */
-    protected $_priority = 5;
-
-    /**
-     * Multi-dimensional array that defines the mapping from OLD table Primary Keys
-     * to NEW table Primary Keys.
-     * Top-level array keys are OLD table names (minus the "wp_" part),
-     * 2nd-level array keys are NEW table names (again, minus the "wp_" part),
-     * 3rd-level array keys are the OLD table primary keys
-     * and 3rd-level array values are the NEW table primary keys
-     *
-     * @var array
-     */
-    protected $_mappings = array();
-
-
-    /**
-     * Returns whether or not this data migration script can operate on the given version of the database.
-     * Eg, if this migration script can migrate from 3.1.26 or higher (but not anything after 4.0.0), and
-     * it's passed a string like '3.1.38B', it should return true.
-     * If this DMS is to migrate data from an EE3 addon, you will probably want to use
-     * EventEspresso\core\services\database\TableAnalysis::tableExists() to check for old EE3 tables, and
-     * EE_Data_Migration_Manager::get_migration_ran() to check that core was already
-     * migrated from EE3 to EE4 (ie, this DMS probably relies on some migration data generated
-     * during the Core 4.1.0 DMS. If core didn't run that DMS, you probably don't want
-     * to run this DMS).
-     * If this DMS migrates data from a previous version of this EE4 addon, just
-     * comparing $current_database_state_of[ $this->slug() ] will probably suffice.
-     * If this DMS should never migrate data, because it's only used to define the initial
-     * database state, just return FALSE (and core's activation process will take care
-     * of calling its schema_changes_before_migration() and
-     * schema_changes_after_migration() for you. )
-     *
-     * @param array $current_database_state_of keys are EE plugin slugs (eg 'Core', 'Calendar', 'Mailchimp', etc)
-     * @return boolean
-     */
-    abstract public function can_migrate_from_version($current_database_state_of);
-
-
-    /**
-     * Performs database schema changes that need to occur BEFORE the data is migrated.
-     * Eg, if we were going to change user passwords from plaintext to encoded versions
-     * during this migration, this would probably add a new column called something like
-     * "encoded_password".
-     *
-     * @return boolean of success
-     */
-    abstract public function schema_changes_before_migration();
-
-
-    /**
-     * Performs the database schema changes that need to occur AFTER the data has been migrated.
-     * Usually this will mean we'll be removing old columns. Eg, if we were changing passwords
-     * from plaintext to encoded versions, and we had added a column called "encoded_password",
-     * this function would probably remove the old column "password" (which still holds the plaintext password)
-     * and possibly rename "encoded_password" to "password"
-     *
-     * @return boolean of success
-     */
-    abstract public function schema_changes_after_migration();
-
-
-    /**
-     * All children of this must call parent::__construct()
-     * at the end of their constructor or suffer the consequences!
-     *
-     * @param TableManager  $table_manager
-     * @param TableAnalysis $table_analysis
-     */
-    public function __construct(TableManager $table_manager = null, TableAnalysis $table_analysis = null)
-    {
-        $this->_migration_stages = (array) apply_filters(
-            'FHEE__' . get_class($this) . '__construct__migration_stages',
-            $this->_migration_stages
-        );
-        foreach ($this->_migration_stages as $migration_stage) {
-            if ($migration_stage instanceof EE_Data_Migration_Script_Stage) {
-                $migration_stage->_construct_finalize($this);
-            }
-        }
-        parent::__construct($table_manager, $table_analysis);
-    }
-
-
-    /**
-     * Place to add hooks and filters for tweaking the migrations page, in order
-     * to customize it
-     */
-    public function migration_page_hooks()
-    {
-        // by default none are added because we normally like the default look of the migration page
-    }
-
-
-    /**
-     * Sets the mapping from old table primary keys to new table primary keys.
-     * This mapping is automatically persisted as a property on the migration
-     *
-     * @param string     $old_table with wpdb prefix (wp_). Eg: wp_events_detail
-     * @param int|string $old_pk    old primary key. Eg events_detail.id's value
-     * @param string     $new_table with wpdb prefix (wp_). Eg: wp_posts
-     * @param int|string $new_pk    eg posts.ID
-     * @return void
-     */
-    public function set_mapping($old_table, $old_pk, $new_table, $new_pk)
-    {
-        // make sure it has the needed keys
-        if (! isset($this->_mappings[ $old_table ]) || ! isset($this->_mappings[ $old_table ][ $new_table ])) {
-            $this->_mappings[ $old_table ][ $new_table ] = $this->_get_mapping_option($old_table, $new_table);
-        }
-        $this->_mappings[ $old_table ][ $new_table ][ $old_pk ] = $new_pk;
-    }
-
-
-    /**
-     * Gets the new primary key, if provided with the OLD table and the primary key
-     * of an item in the old table, and the new table
-     *
-     * @param string     $old_table with wpdb prefix (wp_). Eg: wp_events_detail
-     * @param int|string $old_pk    old primary key. Eg events_detail.id's value
-     * @param string     $new_table with wpdb prefix (wp_). Eg: wp_posts
-     * @return mixed the primary key on the new table
-     */
-    public function get_mapping_new_pk($old_table, $old_pk, $new_table)
-    {
-        if (! isset($this->_mappings[ $old_table ]) ||
-            ! isset($this->_mappings[ $old_table ][ $new_table ])) {
-            // try fetching the option
-            $this->_mappings[ $old_table ][ $new_table ] = $this->_get_mapping_option($old_table, $new_table);
-        }
-        return isset($this->_mappings[ $old_table ][ $new_table ][ $old_pk ])
-            ? $this->_mappings[ $old_table ][ $new_table ][ $old_pk ] : null;
-    }
-
-
-    /**
-     * Gets the old primary key, if provided with the OLD table,
-     * and the new table and the primary key of an item in the new table
-     *
-     * @param string $old_table with wpdb prefix (wp_). Eg: wp_events_detail
-     * @param string $new_table with wpdb prefix (wp_). Eg: wp_posts
-     * @param mixed  $new_pk
-     * @return mixed
-     */
-    public function get_mapping_old_pk($old_table, $new_table, $new_pk)
-    {
-        if (! isset($this->_mappings[ $old_table ]) ||
-            ! isset($this->_mappings[ $old_table ][ $new_table ])) {
-            // try fetching the option
-            $this->_mappings[ $old_table ][ $new_table ] = $this->_get_mapping_option($old_table, $new_table);
-        }
-        if (isset($this->_mappings[ $old_table ][ $new_table ])) {
-            $new_pk_to_old_pk = array_flip($this->_mappings[ $old_table ][ $new_table ]);
-            if (isset($new_pk_to_old_pk[ $new_pk ])) {
-                return $new_pk_to_old_pk[ $new_pk ];
-            }
-        }
-        return null;
-    }
-
-
-    /**
-     * Gets the mapping array option specified by the table names
-     *
-     * @param string $old_table_name
-     * @param string $new_table_name
-     * @return array
-     */
-    protected function _get_mapping_option($old_table_name, $new_table_name)
-    {
-        $option = get_option($this->_get_mapping_option_name($old_table_name, $new_table_name), array());
-        return $option;
-    }
-
-
-    /**
-     * Updates the mapping option specified by the table names with the array provided
-     *
-     * @param string $old_table_name
-     * @param string $new_table_name
-     * @param array  $mapping_array
-     * @return boolean success of updating option
-     */
-    protected function _set_mapping_option($old_table_name, $new_table_name, $mapping_array)
-    {
-        $success = update_option($this->_get_mapping_option_name($old_table_name, $new_table_name), $mapping_array, false);
-        return $success;
-    }
-
-
-    /**
-     * Gets the option name for this script to map from $old_table_name to $new_table_name
-     *
-     * @param string $old_table_name
-     * @param string $new_table_name
-     * @return string
-     */
-    protected function _get_mapping_option_name($old_table_name, $new_table_name)
-    {
-        global $wpdb;
-        $old_table_name_sans_wp = str_replace($wpdb->prefix, "", $old_table_name);
-        $new_table_name_sans_wp = str_replace($wpdb->prefix, "", $new_table_name);
-        $migrates_to = EE_Data_Migration_Manager::instance()->script_migrates_to_version(get_class($this));
-        return substr(
-            EE_Data_Migration_Manager::data_migration_script_mapping_option_prefix . $migrates_to ['slug'] . '_' . $migrates_to['version'] . '_' . $old_table_name_sans_wp . '_' . $new_table_name_sans_wp,
-            0,
-            64
-        );
-    }
-
-
-    /**
-     * Counts all the records that will be migrated during this data migration.
-     * For example, if we were changing old user passwords from plaintext to encoded versions,
-     * this would be a count of all users who have passwords. If we were going to also split
-     * attendee records into transactions, registrations, and attendee records, this would include
-     * the count of all attendees currently in existence in the DB (ie, users + attendees).
-     * If you can't determine how many records there are to migrate, just provide a guess: this
-     * number will only be used in calculating the percent complete. If you estimate there to be
-     * 100 records to migrate, and it turns out there's 120, we'll just show the migration as being at
-     * 99% until the function "migration_step" returns EE_Data_Migration_Script_Base::status_complete.
-     *
-     * @return int
-     */
-    protected function _count_records_to_migrate()
-    {
-        $count = 0;
-        foreach ($this->stages() as $stage) {
-            $count += $stage->count_records_to_migrate();
-        }
-        return $count;
-    }
-
-
-    /**
-     * Returns the number of records updated so far. Usually this is easiest to do
-     * by just setting a transient and updating it after each migration_step
-     *
-     * @return int
-     */
-    public function count_records_migrated()
-    {
-        $count = 0;
-        foreach ($this->stages() as $stage) {
-            $count += $stage->count_records_migrated();
-        }
-        $this->_records_migrated = $count;
-        return $count;
-    }
-
-
-    /**
-     * @param int $num_records_to_migrate_limit
-     * @return int
-     * @throws EE_Error
-     * @throws Exception
-     */
-    public function migration_step($num_records_to_migrate_limit)
-    {
-        // reset the feedback message
-        $this->_feedback_message = '';
-        // if we haven't yet done the 1st schema changes, do them now. buffer any output
-        $this->_maybe_do_schema_changes(true);
-
-        $num_records_actually_migrated = 0;
-        $records_migrated_per_stage = array();
-        // setup the 'stage' variable, which should hold the last run stage of the migration  (or none at all if nothing runs)
-        $stage = null;
-        // get the next stage that isn't complete
-        foreach ($this->stages() as $stage) {
-            if ($stage->get_status() == EE_Data_Migration_Manager::status_continue) {
-                try {
-                    $records_migrated_during_stage = $stage->migration_step(
-                        $num_records_to_migrate_limit - $num_records_actually_migrated
-                    );
-                    $num_records_actually_migrated += $records_migrated_during_stage;
-                    $records_migrated_per_stage[ $stage->pretty_name() ] = $records_migrated_during_stage;
-                } catch (Exception $e) {
-                    // yes if we catch an exception here, we consider that migration stage borked.
-                    $stage->set_status(EE_Data_Migration_Manager::status_fatal_error);
-                    $this->set_status(EE_Data_Migration_Manager::status_fatal_error);
-                    $stage->add_error($e->getMessage() . ". Stack-trace:" . $e->getTraceAsString());
-                    throw $e;
-                }
-                // check that the migration stage didn't mark itself as having a fatal error
-                if ($stage->is_broken()) {
-                    $this->set_broken();
-                    throw new EE_Error($stage->get_last_error());
-                }
-            }
-            // once we've migrated all the number we intended to (possibly from different stages), stop migrating
-            // or if we had a fatal error
-            // or if the current script stopped early- its not done, but it's done all it thinks we should do on this step
-            if ($num_records_actually_migrated >= $num_records_to_migrate_limit
-                || $stage->is_broken()
-                || $stage->has_more_to_do()
-            ) {
-                break;
-            }
-        }
-        // check if we're all done this data migration...
-        // which is indicated by being done early AND the last stage claims to be done
-        if ($stage == null) {
-            // this migration script apparently has NO stages... which is super weird, but whatever
-            $this->set_completed();
-            $this->_maybe_do_schema_changes(false);
-        } elseif ($num_records_actually_migrated < $num_records_to_migrate_limit && ! $stage->has_more_to_do()) {
-            // apparently we're done, because we couldn't migrate the number we intended to
-            $this->set_completed();
-            $this->_update_feedback_message(array_reverse($records_migrated_per_stage));
-            // do schema changes for after the migration now
-            // first double-check we haven't already done this
-            $this->_maybe_do_schema_changes(false);
-        } else {
-            // update feedback message, keeping in mind that we show them with the most recent at the top
-            $this->_update_feedback_message(array_reverse($records_migrated_per_stage));
-        }
-        return $num_records_actually_migrated;
-    }
-
-
-    /**
-     * Updates the feedback message according to what was done during this migration stage.
-     *
-     * @param array $records_migrated_per_stage KEYS are pretty names for each stage; values are the count of records
-     *                                          migrated from that stage
-     * @return void
-     */
-    private function _update_feedback_message($records_migrated_per_stage)
-    {
-        $feedback_message_array = array();
-        foreach ($records_migrated_per_stage as $migration_stage_name => $num_records_migrated) {
-            $feedback_message_array[] = sprintf(
-                __("Migrated %d records successfully during %s", "event_espresso"),
-                $num_records_migrated,
-                $migration_stage_name
-            );
-        }
-        $this->_feedback_message .= implode("<br>", $feedback_message_array);
-    }
-
-
-    /**
-     * Calls either schema_changes_before_migration() (if $before==true) or schema_changes_after_migration
-     * (if $before==false). Buffers their outputs and stores them on the class.
-     *
-     * @param boolean $before
-     * @throws Exception
-     * @return void
-     */
-    private function _maybe_do_schema_changes($before = true)
-    {
-        // so this property will be either _schema_changes_after_migration_ran or _schema_changes_before_migration_ran
-        $property_name = '_schema_changes_' . ($before ? 'before' : 'after') . '_migration_ran';
-        if (! $this->{$property_name}) {
-            try {
-                ob_start();
-                if ($before) {
-                    $this->schema_changes_before_migration();
-                } else {
-                    $this->schema_changes_after_migration();
-                }
-                $output = ob_get_contents();
-                ob_end_clean();
-            } catch (Exception $e) {
-                $this->set_status(EE_Data_Migration_Manager::status_fatal_error);
-                throw $e;
-            }
-            // record that we've done these schema changes
-            $this->{$property_name} = true;
-            // if there were any warnings etc, record them as non-fatal errors
-            if ($output) {
-                // there were some warnings
-                $this->_errors[] = $output;
-            }
-        }
-    }
-
-
-    /**
-     * Wrapper for EEH_Activation::create_table. However, takes into account the request type when
-     * deciding what to pass for its 4th arg, $drop_pre_existing_tables. Using this function, instead
-     * of _table_should_exist_previously, indicates that this table should be new to the EE version being migrated to
-     * or
-     * activated currently. If this is a brand new activation or a migration, and we're indicating this table should
-     * not
-     * previously exist, then we want to set $drop_pre_existing_tables to TRUE (ie, we shouldn't discover that this
-     * table exists in the DB in EEH_Activation::create_table- if it DOES exist, something's wrong and the old table
-     * should be nuked.
-     *
-     * Just for a bit of context, the migration script's db_schema_changes_* methods
-     * are called basically in 3 cases: on brand new activation of EE4 (ie no previous version of EE existed and the
-     * plugin is being activated and we want to add all the brand new tables), upon reactivation of EE4 (it was
-     * deactivated and then reactivated, in which case we want to just verify the DB structure is ok) that table should
-     * be dropped), and during a migration when we're moving the DB to the state of the migration script
-     *
-     * @param string $table_name
-     * @param string $table_definition_sql
-     * @param string $engine_string
-     */
-    protected function _table_is_new_in_this_version(
-        $table_name,
-        $table_definition_sql,
-        $engine_string = 'ENGINE=InnoDB '
-    ) {
-        $this->_create_table_and_catch_errors(
-            $table_name,
-            $table_definition_sql,
-            $engine_string,
-            $this->_pre_existing_table_should_be_dropped(true)
-        );
-    }
-
-    /**
-     * Like _table_is_new_in_this_version and _table_should_exist_previously, this function verifies the given table
-     * exists. But we understand that this table has CHANGED in this version since the previous version. So it's not
-     * completely new, but it's different. So we need to treat it like a new table in terms of verifying it's schema is
-     * correct on activations, migrations, upgrades; but if it exists when it shouldn't, we need to be as lenient as
-     * _table_should_exist_previously.
-     * 8656]{Assumes only this plugin could have added this table (ie, if its a new activation of this plugin, the
-     * table shouldn't exist).
-     *
-     * @param string $table_name
-     * @param string $table_definition_sql
-     * @param string $engine_string
-     */
-    protected function _table_is_changed_in_this_version(
-        $table_name,
-        $table_definition_sql,
-        $engine_string = 'ENGINE=MyISAM'
-    ) {
-        $this->_create_table_and_catch_errors(
-            $table_name,
-            $table_definition_sql,
-            $engine_string,
-            $this->_pre_existing_table_should_be_dropped(false)
-        );
-    }
-
-
-    /**
-     * _old_table_exists
-     * returns TRUE if the requested table exists in the current database
-     *
-     * @param string $table_name
-     * @return boolean
-     */
-    protected function _old_table_exists($table_name)
-    {
-        return $this->_get_table_analysis()->tableExists($table_name);
-    }
-
-
-    /**
-     * _delete_table_if_empty
-     * returns TRUE if the requested table was empty and successfully empty
-     *
-     * @param string $table_name
-     * @return boolean
-     */
-    protected function _delete_table_if_empty($table_name)
-    {
-        return EEH_Activation::delete_db_table_if_empty($table_name);
-    }
-
-
-    /**
-     * It is preferred to use _table_has_not_changed_since_previous or _table_is_changed_in_this_version
-     * as these are significantly more efficient or explicit.
-     * Please see description of _table_is_new_in_this_version. This function will only set
-     * EEH_Activation::create_table's $drop_pre_existing_tables to TRUE if it's a brand
-     * new activation. ie, a more accurate name for this method would be "_table_added_previously_by_this_plugin"
-     * because the table will be cleared out if this is a new activation (ie, if its a new activation, it actually
-     * should exist previously). Otherwise, we'll always set $drop_pre_existing_tables to FALSE because the table
-     * should have existed. Note, if the table is being MODIFIED in this version being activated or migrated to, then
-     * you want _table_is_changed_in_this_version NOT this one. We don't check this table's structure during migrations
-     * because apparently it hasn't changed since the previous one, right?
-     *
-     * @param string $table_name
-     * @param string $table_definition_sql
-     * @param string $engine_string
-     */
-    protected function _table_should_exist_previously(
-        $table_name,
-        $table_definition_sql,
-        $engine_string = 'ENGINE=MyISAM'
-    ) {
-        $this->_create_table_and_catch_errors(
-            $table_name,
-            $table_definition_sql,
-            $engine_string,
-            $this->_pre_existing_table_should_be_dropped(false)
-        );
-    }
-
-    /**
-     * Exactly the same as _table_should_exist_previously(), except if this migration script is currently doing
-     * a migration, we skip checking this table's structure in the database and just assume it's correct.
-     * So this is useful only to improve efficiency when doing migrations (not a big deal for single site installs,
-     * but important for multisite where migrations can take a very long time otherwise).
-     * If the table is known to have changed since previous version, use _table_is_changed_in_this_version().
-     * Assumes only this plugin could have added this table (ie, if its a new activation of this plugin, the table
-     * shouldn't exist).
-     *
-     * @param string $table_name
-     * @param string $table_definition_sql
-     * @param string $engine_string
-     */
-    protected function _table_has_not_changed_since_previous(
-        $table_name,
-        $table_definition_sql,
-        $engine_string = 'ENGINE=MyISAM'
-    ) {
-        if ($this->_currently_migrating()) {
-            // if we're doing a migration, and this table apparently already exists, then we don't need do anything right?
-            return;
-        }
-        $this->_create_table_and_catch_errors(
-            $table_name,
-            $table_definition_sql,
-            $engine_string,
-            $this->_pre_existing_table_should_be_dropped(false)
-        );
-    }
-
-    /**
-     * Returns whether or not this migration script is being used as part of an actual migration
-     *
-     * @return boolean
-     */
-    protected function _currently_migrating()
-    {
-        // we want to know if we are currently performing a migration. We could just believe what was set on the _migrating property, but let's double-check (ie the script should apply and we should be in MM)
-        return $this->_migrating &&
-               $this->can_migrate_from_version(
-                   EE_Data_Migration_Manager::instance()->ensure_current_database_state_is_set()
-               ) &&
-               EE_Maintenance_Mode::instance()->real_level() == EE_Maintenance_Mode::level_2_complete_maintenance;
-    }
-
-    /**
-     * Determines if a table should be dropped, based on whether it's reported to be new in $table_is_new,
-     * and the plugin's request type.
-     * Assumes only this plugin could have added the table (ie, if its a new activation of this plugin, the table
-     * shouldn't exist no matter what).
-     *
-     * @param boolean $table_is_new
-     * @return boolean
-     */
-    protected function _pre_existing_table_should_be_dropped($table_is_new)
-    {
-        if ($table_is_new) {
-            if ($this->_get_req_type_for_plugin_corresponding_to_this_dms() == EE_System::req_type_new_activation
-                || $this->_currently_migrating()
-            ) {
-                return true;
-            } else {
-                return false;
-            }
-        } else {
-            if (in_array(
-                $this->_get_req_type_for_plugin_corresponding_to_this_dms(),
-                array(EE_System::req_type_new_activation)
-            )) {
-                return true;
-            } else {
-                return false;
-            }
-        }
-    }
-
-    /**
-     * Just wraps EEH_Activation::create_table, but catches any errors it may throw and adds them as errors on the DMS
-     *
-     * @param string  $table_name
-     * @param string  $table_definition_sql
-     * @param string  $engine_string
-     * @param boolean $drop_pre_existing_tables
-     */
-    private function _create_table_and_catch_errors(
-        $table_name,
-        $table_definition_sql,
-        $engine_string = 'ENGINE=MyISAM',
-        $drop_pre_existing_tables = false
-    ) {
-        try {
-            EEH_Activation::create_table($table_name, $table_definition_sql, $engine_string, $drop_pre_existing_tables);
-        } catch (EE_Error $e) {
-            $message = $e->getMessage() . '<br>Stack Trace:' . $e->getTraceAsString();
-            $this->add_error($message);
-            $this->_feedback_message .= $message;
-        }
-    }
-
-
-    /**
-     * Gets the request type for the plugin (core or addon) that corresponds to this DMS
-     *
-     * @return int one of EE_System::_req_type_* constants
-     * @throws EE_Error
-     */
-    private function _get_req_type_for_plugin_corresponding_to_this_dms()
-    {
-        if ($this->slug() == 'Core') {
-            return EE_System::instance()->detect_req_type();
-        } else {// it must be for an addon
-            $addon_name = $this->slug();
-            if (EE_Registry::instance()->get_addon_by_name($addon_name)) {
-                return EE_Registry::instance()->get_addon_by_name($addon_name)->detect_req_type();
-            } else {
-                throw new EE_Error(
-                    sprintf(
-                        __(
-                            "The DMS slug '%s' should correspond to the addon's name, which should also be '%s', but no such addon was registered. These are the registered addons' names: %s",
-                            "event_espresso"
-                        ),
-                        $this->slug(),
-                        $addon_name,
-                        implode(",", array_keys(EE_Registry::instance()->get_addons_by_name()))
-                    )
-                );
-            }
-        }
-    }
-
-
-    /**
-     * returns an array of strings describing errors by all the script's stages
-     *
-     * @return array
-     */
-    public function get_errors()
-    {
-        $all_errors = $this->_errors;
-        if (! is_array($all_errors)) {
-            $all_errors = array();
-        }
-        foreach ($this->stages() as $stage) {
-            $all_errors = array_merge($stage->get_errors(), $all_errors);
-        }
-        return $all_errors;
-    }
-
-
-    /**
-     * Indicates whether or not this migration script should continue
-     *
-     * @return boolean
-     */
-    public function can_continue()
-    {
-        return in_array(
-            $this->get_status(),
-            EE_Data_Migration_Manager::instance()->stati_that_indicate_to_continue_single_migration_script
-        );
-    }
-
-
-    /**
-     * Gets all the data migration stages associated with this script. Note:
-     * addons can filter this list to add their own stages, and because the list is
-     * numerically-indexed, they can insert their stage wherever they like and it will
-     * get ordered by the indexes
-     *
-     * @return EE_Data_Migration_Script_Stage[]
-     */
-    protected function stages()
-    {
-        $stages = apply_filters('FHEE__' . get_class($this) . '__stages', $this->_migration_stages);
-        ksort($stages);
-        return $stages;
-    }
-
-
-    /**
-     * Gets a string which should describe what's going on currently with this migration, which
-     * can be displayed to the user
-     *
-     * @return string
-     */
-    public function get_feedback_message()
-    {
-        return $this->_feedback_message;
-    }
-
-
-    /**
-     * A lot like "__sleep()" magic method in purpose, this is meant for persisting this class'
-     * properties to the DB. However, we don't want to use __sleep() because its quite
-     * possible that this class is defined when it goes to sleep, but NOT available when it
-     * awakes (eg, this class is part of an addon that is deactivated at some point).
-     */
-    public function properties_as_array()
-    {
-        $properties = parent::properties_as_array();
-        $properties['_migration_stages'] = array();
-        foreach ($this->_migration_stages as $migration_stage_priority => $migration_stage_class) {
-            $properties['_migration_stages'][ $migration_stage_priority ] = $migration_stage_class->properties_as_array(
-            );
-        }
-        unset($properties['_mappings']);
-
-        foreach ($this->_mappings as $old_table_name => $mapping_to_new_table) {
-            foreach ($mapping_to_new_table as $new_table_name => $mapping) {
-                $this->_set_mapping_option($old_table_name, $new_table_name, $mapping);
-            }
-        }
-        return $properties;
-    }
-
-
-    /**
-     * Sets all of the properties of this script stage to match what's in the array, which is assumed
-     * to have been made from the properties_as_array() function.
-     *
-     * @param array $array_of_properties like what's produced from properties_as_array() method
-     * @return void
-     */
-    public function instantiate_from_array_of_properties($array_of_properties)
-    {
-        $stages_properties_arrays = $array_of_properties['_migration_stages'];
-        unset($array_of_properties['_migration_stages']);
-        unset($array_of_properties['class']);
-        foreach ($array_of_properties as $property_name => $property_value) {
-            $this->{$property_name} = $property_value;
-        }
-        // _migration_stages are already instantiated, but have only default data
-        foreach ($this->_migration_stages as $stage) {
-            $stage_data = $this->_find_migration_stage_data_with_classname(
-                get_class($stage),
-                $stages_properties_arrays
-            );
-            // SO, if we found the stage data that was saved, use it. Otherwise, I guess the stage is new? (maybe added by
-            // an addon? Unlikely... not sure why it wouldn't exist, but if it doesn't just treat it like it was never started yet)
-            if ($stage_data) {
-                $stage->instantiate_from_array_of_properties($stage_data);
-            }
-        }
-    }
-
-
-    /**
-     * Gets the migration data from the array $migration_stage_data_arrays (which is an array of arrays, each of which
-     * is pretty well identical to EE_Data_Migration_Stage objects except all their properties are array indexes)
-     * for the given classname
-     *
-     * @param string $classname
-     * @param array  $migration_stage_data_arrays
-     * @return null
-     */
-    private function _find_migration_stage_data_with_classname($classname, $migration_stage_data_arrays)
-    {
-        foreach ($migration_stage_data_arrays as $migration_stage_data_array) {
-            if (isset($migration_stage_data_array['class']) && $migration_stage_data_array['class'] == $classname) {
-                return $migration_stage_data_array;
-            }
-        }
-        return null;
-    }
-
-
-    /**
-     * Returns the version that this script migrates to, based on the script's name.
-     * Cannot be overwritten because lots of code needs to know which version a script
-     * migrates to knowing only its name.
-     *
-     * @return array where the first key is the plugin's slug, the 2nd is the version of that plugin
-     * that will be updated to. Eg array('Core','4.1.0')
-     */
-    final public function migrates_to_version()
-    {
-        return EE_Data_Migration_Manager::instance()->script_migrates_to_version(get_class($this));
-    }
-
-
-    /**
-     * Gets this addon's slug as it would appear in the current_db_state wp option,
-     * and if this migration script is for an addon, it SHOULD match the addon's slug
-     * (and also the addon's classname, minus the 'EE_' prefix.). Eg, 'Calendar' for the EE_Calendar addon.
-     * Or 'Core' for core (non-addon).
-     *
-     * @return string
-     */
-    public function slug()
-    {
-        $migrates_to_version_info = $this->migrates_to_version();
-        // the slug is the first part of the array
-        return $migrates_to_version_info['slug'];
-    }
-
-
-    /**
-     * Returns the script's priority relative to DMSs from other addons. However, when
-     * two DMSs from the same addon/core apply, this is ignored (and instead the version that
-     * the script migrates to is used to determine which to run first). The default is 5, but all core DMSs
-     * normally have priority 10. (So if you want a DMS "A" to run before DMS "B", both of which are from addons,
-     * and both of which CAN run at the same time (ie, "B" doesn't depend on "A" to set
-     * the database up so it can run), then you can set "A" to priority 3 or something.
-     *
-     * @return int
-     */
-    public function priority()
-    {
-        return $this->_priority;
-    }
-
-
-    /**
-     * Sets whether or not this DMS is being ran as part of a migration, instead of
-     * just being used to setup (or verify) the current database structure matches
-     * what the latest DMS indicates it should be
-     *
-     * @param boolean $migrating
-     * @return void
-     */
-    public function set_migrating($migrating = true)
-    {
-        $this->_migrating = $migrating;
-    }
-
-    /**
-     * Marks that we think this migration class can continue to migrate
-     */
-    public function reattempt()
-    {
-        parent::reattempt();
-        // also, we want to reattempt any stages that were marked as borked
-        foreach ($this->stages() as $stage) {
-            if ($stage->is_broken()) {
-                $stage->reattempt();
-            }
-        }
-    }
+	/**
+	 * Set by client code to indicate this DMS is being ran as part of a proper migration,
+	 * instead of being used to merely setup (or verify) the database structure.
+	 * Defaults to TRUE, so client code that's NOT using this DMS as part of a proper migration
+	 * should call EE_Data_Migration_Script_Base::set_migrating( FALSE )
+	 *
+	 * @var boolean
+	 */
+	protected $_migrating = true;
+
+	/**
+	 * numerically-indexed array where each value is EE_Data_Migration_Script_Stage object
+	 *
+	 * @var EE_Data_Migration_Script_Stage[] $migration_functions
+	 */
+	protected $_migration_stages = array();
+
+	/**
+	 * Indicates we've already ran the schema changes that needed to happen BEFORE the data migration
+	 *
+	 * @var boolean
+	 */
+	protected $_schema_changes_before_migration_ran = null;
+
+	/**
+	 * Indicates we've already ran the schema changes that needed to happen AFTER the data migration
+	 *
+	 * @var boolean
+	 */
+	protected $_schema_changes_after_migration_ran = null;
+
+	/**
+	 * String which describes what's currently happening in this migration
+	 *
+	 * @var string
+	 */
+	protected $_feedback_message;
+
+	/**
+	 * Indicates the script's priority. Like wp's add_action and add_filter, lower numbers
+	 * correspond to earlier execution
+	 *
+	 * @var int
+	 */
+	protected $_priority = 5;
+
+	/**
+	 * Multi-dimensional array that defines the mapping from OLD table Primary Keys
+	 * to NEW table Primary Keys.
+	 * Top-level array keys are OLD table names (minus the "wp_" part),
+	 * 2nd-level array keys are NEW table names (again, minus the "wp_" part),
+	 * 3rd-level array keys are the OLD table primary keys
+	 * and 3rd-level array values are the NEW table primary keys
+	 *
+	 * @var array
+	 */
+	protected $_mappings = array();
+
+
+	/**
+	 * Returns whether or not this data migration script can operate on the given version of the database.
+	 * Eg, if this migration script can migrate from 3.1.26 or higher (but not anything after 4.0.0), and
+	 * it's passed a string like '3.1.38B', it should return true.
+	 * If this DMS is to migrate data from an EE3 addon, you will probably want to use
+	 * EventEspresso\core\services\database\TableAnalysis::tableExists() to check for old EE3 tables, and
+	 * EE_Data_Migration_Manager::get_migration_ran() to check that core was already
+	 * migrated from EE3 to EE4 (ie, this DMS probably relies on some migration data generated
+	 * during the Core 4.1.0 DMS. If core didn't run that DMS, you probably don't want
+	 * to run this DMS).
+	 * If this DMS migrates data from a previous version of this EE4 addon, just
+	 * comparing $current_database_state_of[ $this->slug() ] will probably suffice.
+	 * If this DMS should never migrate data, because it's only used to define the initial
+	 * database state, just return FALSE (and core's activation process will take care
+	 * of calling its schema_changes_before_migration() and
+	 * schema_changes_after_migration() for you. )
+	 *
+	 * @param array $current_database_state_of keys are EE plugin slugs (eg 'Core', 'Calendar', 'Mailchimp', etc)
+	 * @return boolean
+	 */
+	abstract public function can_migrate_from_version($current_database_state_of);
+
+
+	/**
+	 * Performs database schema changes that need to occur BEFORE the data is migrated.
+	 * Eg, if we were going to change user passwords from plaintext to encoded versions
+	 * during this migration, this would probably add a new column called something like
+	 * "encoded_password".
+	 *
+	 * @return boolean of success
+	 */
+	abstract public function schema_changes_before_migration();
+
+
+	/**
+	 * Performs the database schema changes that need to occur AFTER the data has been migrated.
+	 * Usually this will mean we'll be removing old columns. Eg, if we were changing passwords
+	 * from plaintext to encoded versions, and we had added a column called "encoded_password",
+	 * this function would probably remove the old column "password" (which still holds the plaintext password)
+	 * and possibly rename "encoded_password" to "password"
+	 *
+	 * @return boolean of success
+	 */
+	abstract public function schema_changes_after_migration();
+
+
+	/**
+	 * All children of this must call parent::__construct()
+	 * at the end of their constructor or suffer the consequences!
+	 *
+	 * @param TableManager  $table_manager
+	 * @param TableAnalysis $table_analysis
+	 */
+	public function __construct(TableManager $table_manager = null, TableAnalysis $table_analysis = null)
+	{
+		$this->_migration_stages = (array) apply_filters(
+			'FHEE__' . get_class($this) . '__construct__migration_stages',
+			$this->_migration_stages
+		);
+		foreach ($this->_migration_stages as $migration_stage) {
+			if ($migration_stage instanceof EE_Data_Migration_Script_Stage) {
+				$migration_stage->_construct_finalize($this);
+			}
+		}
+		parent::__construct($table_manager, $table_analysis);
+	}
+
+
+	/**
+	 * Place to add hooks and filters for tweaking the migrations page, in order
+	 * to customize it
+	 */
+	public function migration_page_hooks()
+	{
+		// by default none are added because we normally like the default look of the migration page
+	}
+
+
+	/**
+	 * Sets the mapping from old table primary keys to new table primary keys.
+	 * This mapping is automatically persisted as a property on the migration
+	 *
+	 * @param string     $old_table with wpdb prefix (wp_). Eg: wp_events_detail
+	 * @param int|string $old_pk    old primary key. Eg events_detail.id's value
+	 * @param string     $new_table with wpdb prefix (wp_). Eg: wp_posts
+	 * @param int|string $new_pk    eg posts.ID
+	 * @return void
+	 */
+	public function set_mapping($old_table, $old_pk, $new_table, $new_pk)
+	{
+		// make sure it has the needed keys
+		if (! isset($this->_mappings[ $old_table ]) || ! isset($this->_mappings[ $old_table ][ $new_table ])) {
+			$this->_mappings[ $old_table ][ $new_table ] = $this->_get_mapping_option($old_table, $new_table);
+		}
+		$this->_mappings[ $old_table ][ $new_table ][ $old_pk ] = $new_pk;
+	}
+
+
+	/**
+	 * Gets the new primary key, if provided with the OLD table and the primary key
+	 * of an item in the old table, and the new table
+	 *
+	 * @param string     $old_table with wpdb prefix (wp_). Eg: wp_events_detail
+	 * @param int|string $old_pk    old primary key. Eg events_detail.id's value
+	 * @param string     $new_table with wpdb prefix (wp_). Eg: wp_posts
+	 * @return mixed the primary key on the new table
+	 */
+	public function get_mapping_new_pk($old_table, $old_pk, $new_table)
+	{
+		if (! isset($this->_mappings[ $old_table ]) ||
+			! isset($this->_mappings[ $old_table ][ $new_table ])) {
+			// try fetching the option
+			$this->_mappings[ $old_table ][ $new_table ] = $this->_get_mapping_option($old_table, $new_table);
+		}
+		return isset($this->_mappings[ $old_table ][ $new_table ][ $old_pk ])
+			? $this->_mappings[ $old_table ][ $new_table ][ $old_pk ] : null;
+	}
+
+
+	/**
+	 * Gets the old primary key, if provided with the OLD table,
+	 * and the new table and the primary key of an item in the new table
+	 *
+	 * @param string $old_table with wpdb prefix (wp_). Eg: wp_events_detail
+	 * @param string $new_table with wpdb prefix (wp_). Eg: wp_posts
+	 * @param mixed  $new_pk
+	 * @return mixed
+	 */
+	public function get_mapping_old_pk($old_table, $new_table, $new_pk)
+	{
+		if (! isset($this->_mappings[ $old_table ]) ||
+			! isset($this->_mappings[ $old_table ][ $new_table ])) {
+			// try fetching the option
+			$this->_mappings[ $old_table ][ $new_table ] = $this->_get_mapping_option($old_table, $new_table);
+		}
+		if (isset($this->_mappings[ $old_table ][ $new_table ])) {
+			$new_pk_to_old_pk = array_flip($this->_mappings[ $old_table ][ $new_table ]);
+			if (isset($new_pk_to_old_pk[ $new_pk ])) {
+				return $new_pk_to_old_pk[ $new_pk ];
+			}
+		}
+		return null;
+	}
+
+
+	/**
+	 * Gets the mapping array option specified by the table names
+	 *
+	 * @param string $old_table_name
+	 * @param string $new_table_name
+	 * @return array
+	 */
+	protected function _get_mapping_option($old_table_name, $new_table_name)
+	{
+		$option = get_option($this->_get_mapping_option_name($old_table_name, $new_table_name), array());
+		return $option;
+	}
+
+
+	/**
+	 * Updates the mapping option specified by the table names with the array provided
+	 *
+	 * @param string $old_table_name
+	 * @param string $new_table_name
+	 * @param array  $mapping_array
+	 * @return boolean success of updating option
+	 */
+	protected function _set_mapping_option($old_table_name, $new_table_name, $mapping_array)
+	{
+		$success = update_option($this->_get_mapping_option_name($old_table_name, $new_table_name), $mapping_array, false);
+		return $success;
+	}
+
+
+	/**
+	 * Gets the option name for this script to map from $old_table_name to $new_table_name
+	 *
+	 * @param string $old_table_name
+	 * @param string $new_table_name
+	 * @return string
+	 */
+	protected function _get_mapping_option_name($old_table_name, $new_table_name)
+	{
+		global $wpdb;
+		$old_table_name_sans_wp = str_replace($wpdb->prefix, "", $old_table_name);
+		$new_table_name_sans_wp = str_replace($wpdb->prefix, "", $new_table_name);
+		$migrates_to = EE_Data_Migration_Manager::instance()->script_migrates_to_version(get_class($this));
+		return substr(
+			EE_Data_Migration_Manager::data_migration_script_mapping_option_prefix . $migrates_to ['slug'] . '_' . $migrates_to['version'] . '_' . $old_table_name_sans_wp . '_' . $new_table_name_sans_wp,
+			0,
+			64
+		);
+	}
+
+
+	/**
+	 * Counts all the records that will be migrated during this data migration.
+	 * For example, if we were changing old user passwords from plaintext to encoded versions,
+	 * this would be a count of all users who have passwords. If we were going to also split
+	 * attendee records into transactions, registrations, and attendee records, this would include
+	 * the count of all attendees currently in existence in the DB (ie, users + attendees).
+	 * If you can't determine how many records there are to migrate, just provide a guess: this
+	 * number will only be used in calculating the percent complete. If you estimate there to be
+	 * 100 records to migrate, and it turns out there's 120, we'll just show the migration as being at
+	 * 99% until the function "migration_step" returns EE_Data_Migration_Script_Base::status_complete.
+	 *
+	 * @return int
+	 */
+	protected function _count_records_to_migrate()
+	{
+		$count = 0;
+		foreach ($this->stages() as $stage) {
+			$count += $stage->count_records_to_migrate();
+		}
+		return $count;
+	}
+
+
+	/**
+	 * Returns the number of records updated so far. Usually this is easiest to do
+	 * by just setting a transient and updating it after each migration_step
+	 *
+	 * @return int
+	 */
+	public function count_records_migrated()
+	{
+		$count = 0;
+		foreach ($this->stages() as $stage) {
+			$count += $stage->count_records_migrated();
+		}
+		$this->_records_migrated = $count;
+		return $count;
+	}
+
+
+	/**
+	 * @param int $num_records_to_migrate_limit
+	 * @return int
+	 * @throws EE_Error
+	 * @throws Exception
+	 */
+	public function migration_step($num_records_to_migrate_limit)
+	{
+		// reset the feedback message
+		$this->_feedback_message = '';
+		// if we haven't yet done the 1st schema changes, do them now. buffer any output
+		$this->_maybe_do_schema_changes(true);
+
+		$num_records_actually_migrated = 0;
+		$records_migrated_per_stage = array();
+		// setup the 'stage' variable, which should hold the last run stage of the migration  (or none at all if nothing runs)
+		$stage = null;
+		// get the next stage that isn't complete
+		foreach ($this->stages() as $stage) {
+			if ($stage->get_status() == EE_Data_Migration_Manager::status_continue) {
+				try {
+					$records_migrated_during_stage = $stage->migration_step(
+						$num_records_to_migrate_limit - $num_records_actually_migrated
+					);
+					$num_records_actually_migrated += $records_migrated_during_stage;
+					$records_migrated_per_stage[ $stage->pretty_name() ] = $records_migrated_during_stage;
+				} catch (Exception $e) {
+					// yes if we catch an exception here, we consider that migration stage borked.
+					$stage->set_status(EE_Data_Migration_Manager::status_fatal_error);
+					$this->set_status(EE_Data_Migration_Manager::status_fatal_error);
+					$stage->add_error($e->getMessage() . ". Stack-trace:" . $e->getTraceAsString());
+					throw $e;
+				}
+				// check that the migration stage didn't mark itself as having a fatal error
+				if ($stage->is_broken()) {
+					$this->set_broken();
+					throw new EE_Error($stage->get_last_error());
+				}
+			}
+			// once we've migrated all the number we intended to (possibly from different stages), stop migrating
+			// or if we had a fatal error
+			// or if the current script stopped early- its not done, but it's done all it thinks we should do on this step
+			if ($num_records_actually_migrated >= $num_records_to_migrate_limit
+				|| $stage->is_broken()
+				|| $stage->has_more_to_do()
+			) {
+				break;
+			}
+		}
+		// check if we're all done this data migration...
+		// which is indicated by being done early AND the last stage claims to be done
+		if ($stage == null) {
+			// this migration script apparently has NO stages... which is super weird, but whatever
+			$this->set_completed();
+			$this->_maybe_do_schema_changes(false);
+		} elseif ($num_records_actually_migrated < $num_records_to_migrate_limit && ! $stage->has_more_to_do()) {
+			// apparently we're done, because we couldn't migrate the number we intended to
+			$this->set_completed();
+			$this->_update_feedback_message(array_reverse($records_migrated_per_stage));
+			// do schema changes for after the migration now
+			// first double-check we haven't already done this
+			$this->_maybe_do_schema_changes(false);
+		} else {
+			// update feedback message, keeping in mind that we show them with the most recent at the top
+			$this->_update_feedback_message(array_reverse($records_migrated_per_stage));
+		}
+		return $num_records_actually_migrated;
+	}
+
+
+	/**
+	 * Updates the feedback message according to what was done during this migration stage.
+	 *
+	 * @param array $records_migrated_per_stage KEYS are pretty names for each stage; values are the count of records
+	 *                                          migrated from that stage
+	 * @return void
+	 */
+	private function _update_feedback_message($records_migrated_per_stage)
+	{
+		$feedback_message_array = array();
+		foreach ($records_migrated_per_stage as $migration_stage_name => $num_records_migrated) {
+			$feedback_message_array[] = sprintf(
+				__("Migrated %d records successfully during %s", "event_espresso"),
+				$num_records_migrated,
+				$migration_stage_name
+			);
+		}
+		$this->_feedback_message .= implode("<br>", $feedback_message_array);
+	}
+
+
+	/**
+	 * Calls either schema_changes_before_migration() (if $before==true) or schema_changes_after_migration
+	 * (if $before==false). Buffers their outputs and stores them on the class.
+	 *
+	 * @param boolean $before
+	 * @throws Exception
+	 * @return void
+	 */
+	private function _maybe_do_schema_changes($before = true)
+	{
+		// so this property will be either _schema_changes_after_migration_ran or _schema_changes_before_migration_ran
+		$property_name = '_schema_changes_' . ($before ? 'before' : 'after') . '_migration_ran';
+		if (! $this->{$property_name}) {
+			try {
+				ob_start();
+				if ($before) {
+					$this->schema_changes_before_migration();
+				} else {
+					$this->schema_changes_after_migration();
+				}
+				$output = ob_get_contents();
+				ob_end_clean();
+			} catch (Exception $e) {
+				$this->set_status(EE_Data_Migration_Manager::status_fatal_error);
+				throw $e;
+			}
+			// record that we've done these schema changes
+			$this->{$property_name} = true;
+			// if there were any warnings etc, record them as non-fatal errors
+			if ($output) {
+				// there were some warnings
+				$this->_errors[] = $output;
+			}
+		}
+	}
+
+
+	/**
+	 * Wrapper for EEH_Activation::create_table. However, takes into account the request type when
+	 * deciding what to pass for its 4th arg, $drop_pre_existing_tables. Using this function, instead
+	 * of _table_should_exist_previously, indicates that this table should be new to the EE version being migrated to
+	 * or
+	 * activated currently. If this is a brand new activation or a migration, and we're indicating this table should
+	 * not
+	 * previously exist, then we want to set $drop_pre_existing_tables to TRUE (ie, we shouldn't discover that this
+	 * table exists in the DB in EEH_Activation::create_table- if it DOES exist, something's wrong and the old table
+	 * should be nuked.
+	 *
+	 * Just for a bit of context, the migration script's db_schema_changes_* methods
+	 * are called basically in 3 cases: on brand new activation of EE4 (ie no previous version of EE existed and the
+	 * plugin is being activated and we want to add all the brand new tables), upon reactivation of EE4 (it was
+	 * deactivated and then reactivated, in which case we want to just verify the DB structure is ok) that table should
+	 * be dropped), and during a migration when we're moving the DB to the state of the migration script
+	 *
+	 * @param string $table_name
+	 * @param string $table_definition_sql
+	 * @param string $engine_string
+	 */
+	protected function _table_is_new_in_this_version(
+		$table_name,
+		$table_definition_sql,
+		$engine_string = 'ENGINE=InnoDB '
+	) {
+		$this->_create_table_and_catch_errors(
+			$table_name,
+			$table_definition_sql,
+			$engine_string,
+			$this->_pre_existing_table_should_be_dropped(true)
+		);
+	}
+
+	/**
+	 * Like _table_is_new_in_this_version and _table_should_exist_previously, this function verifies the given table
+	 * exists. But we understand that this table has CHANGED in this version since the previous version. So it's not
+	 * completely new, but it's different. So we need to treat it like a new table in terms of verifying it's schema is
+	 * correct on activations, migrations, upgrades; but if it exists when it shouldn't, we need to be as lenient as
+	 * _table_should_exist_previously.
+	 * 8656]{Assumes only this plugin could have added this table (ie, if its a new activation of this plugin, the
+	 * table shouldn't exist).
+	 *
+	 * @param string $table_name
+	 * @param string $table_definition_sql
+	 * @param string $engine_string
+	 */
+	protected function _table_is_changed_in_this_version(
+		$table_name,
+		$table_definition_sql,
+		$engine_string = 'ENGINE=MyISAM'
+	) {
+		$this->_create_table_and_catch_errors(
+			$table_name,
+			$table_definition_sql,
+			$engine_string,
+			$this->_pre_existing_table_should_be_dropped(false)
+		);
+	}
+
+
+	/**
+	 * _old_table_exists
+	 * returns TRUE if the requested table exists in the current database
+	 *
+	 * @param string $table_name
+	 * @return boolean
+	 */
+	protected function _old_table_exists($table_name)
+	{
+		return $this->_get_table_analysis()->tableExists($table_name);
+	}
+
+
+	/**
+	 * _delete_table_if_empty
+	 * returns TRUE if the requested table was empty and successfully empty
+	 *
+	 * @param string $table_name
+	 * @return boolean
+	 */
+	protected function _delete_table_if_empty($table_name)
+	{
+		return EEH_Activation::delete_db_table_if_empty($table_name);
+	}
+
+
+	/**
+	 * It is preferred to use _table_has_not_changed_since_previous or _table_is_changed_in_this_version
+	 * as these are significantly more efficient or explicit.
+	 * Please see description of _table_is_new_in_this_version. This function will only set
+	 * EEH_Activation::create_table's $drop_pre_existing_tables to TRUE if it's a brand
+	 * new activation. ie, a more accurate name for this method would be "_table_added_previously_by_this_plugin"
+	 * because the table will be cleared out if this is a new activation (ie, if its a new activation, it actually
+	 * should exist previously). Otherwise, we'll always set $drop_pre_existing_tables to FALSE because the table
+	 * should have existed. Note, if the table is being MODIFIED in this version being activated or migrated to, then
+	 * you want _table_is_changed_in_this_version NOT this one. We don't check this table's structure during migrations
+	 * because apparently it hasn't changed since the previous one, right?
+	 *
+	 * @param string $table_name
+	 * @param string $table_definition_sql
+	 * @param string $engine_string
+	 */
+	protected function _table_should_exist_previously(
+		$table_name,
+		$table_definition_sql,
+		$engine_string = 'ENGINE=MyISAM'
+	) {
+		$this->_create_table_and_catch_errors(
+			$table_name,
+			$table_definition_sql,
+			$engine_string,
+			$this->_pre_existing_table_should_be_dropped(false)
+		);
+	}
+
+	/**
+	 * Exactly the same as _table_should_exist_previously(), except if this migration script is currently doing
+	 * a migration, we skip checking this table's structure in the database and just assume it's correct.
+	 * So this is useful only to improve efficiency when doing migrations (not a big deal for single site installs,
+	 * but important for multisite where migrations can take a very long time otherwise).
+	 * If the table is known to have changed since previous version, use _table_is_changed_in_this_version().
+	 * Assumes only this plugin could have added this table (ie, if its a new activation of this plugin, the table
+	 * shouldn't exist).
+	 *
+	 * @param string $table_name
+	 * @param string $table_definition_sql
+	 * @param string $engine_string
+	 */
+	protected function _table_has_not_changed_since_previous(
+		$table_name,
+		$table_definition_sql,
+		$engine_string = 'ENGINE=MyISAM'
+	) {
+		if ($this->_currently_migrating()) {
+			// if we're doing a migration, and this table apparently already exists, then we don't need do anything right?
+			return;
+		}
+		$this->_create_table_and_catch_errors(
+			$table_name,
+			$table_definition_sql,
+			$engine_string,
+			$this->_pre_existing_table_should_be_dropped(false)
+		);
+	}
+
+	/**
+	 * Returns whether or not this migration script is being used as part of an actual migration
+	 *
+	 * @return boolean
+	 */
+	protected function _currently_migrating()
+	{
+		// we want to know if we are currently performing a migration. We could just believe what was set on the _migrating property, but let's double-check (ie the script should apply and we should be in MM)
+		return $this->_migrating &&
+			   $this->can_migrate_from_version(
+				   EE_Data_Migration_Manager::instance()->ensure_current_database_state_is_set()
+			   ) &&
+			   EE_Maintenance_Mode::instance()->real_level() == EE_Maintenance_Mode::level_2_complete_maintenance;
+	}
+
+	/**
+	 * Determines if a table should be dropped, based on whether it's reported to be new in $table_is_new,
+	 * and the plugin's request type.
+	 * Assumes only this plugin could have added the table (ie, if its a new activation of this plugin, the table
+	 * shouldn't exist no matter what).
+	 *
+	 * @param boolean $table_is_new
+	 * @return boolean
+	 */
+	protected function _pre_existing_table_should_be_dropped($table_is_new)
+	{
+		if ($table_is_new) {
+			if ($this->_get_req_type_for_plugin_corresponding_to_this_dms() == EE_System::req_type_new_activation
+				|| $this->_currently_migrating()
+			) {
+				return true;
+			} else {
+				return false;
+			}
+		} else {
+			if (in_array(
+				$this->_get_req_type_for_plugin_corresponding_to_this_dms(),
+				array(EE_System::req_type_new_activation)
+			)) {
+				return true;
+			} else {
+				return false;
+			}
+		}
+	}
+
+	/**
+	 * Just wraps EEH_Activation::create_table, but catches any errors it may throw and adds them as errors on the DMS
+	 *
+	 * @param string  $table_name
+	 * @param string  $table_definition_sql
+	 * @param string  $engine_string
+	 * @param boolean $drop_pre_existing_tables
+	 */
+	private function _create_table_and_catch_errors(
+		$table_name,
+		$table_definition_sql,
+		$engine_string = 'ENGINE=MyISAM',
+		$drop_pre_existing_tables = false
+	) {
+		try {
+			EEH_Activation::create_table($table_name, $table_definition_sql, $engine_string, $drop_pre_existing_tables);
+		} catch (EE_Error $e) {
+			$message = $e->getMessage() . '<br>Stack Trace:' . $e->getTraceAsString();
+			$this->add_error($message);
+			$this->_feedback_message .= $message;
+		}
+	}
+
+
+	/**
+	 * Gets the request type for the plugin (core or addon) that corresponds to this DMS
+	 *
+	 * @return int one of EE_System::_req_type_* constants
+	 * @throws EE_Error
+	 */
+	private function _get_req_type_for_plugin_corresponding_to_this_dms()
+	{
+		if ($this->slug() == 'Core') {
+			return EE_System::instance()->detect_req_type();
+		} else {// it must be for an addon
+			$addon_name = $this->slug();
+			if (EE_Registry::instance()->get_addon_by_name($addon_name)) {
+				return EE_Registry::instance()->get_addon_by_name($addon_name)->detect_req_type();
+			} else {
+				throw new EE_Error(
+					sprintf(
+						__(
+							"The DMS slug '%s' should correspond to the addon's name, which should also be '%s', but no such addon was registered. These are the registered addons' names: %s",
+							"event_espresso"
+						),
+						$this->slug(),
+						$addon_name,
+						implode(",", array_keys(EE_Registry::instance()->get_addons_by_name()))
+					)
+				);
+			}
+		}
+	}
+
+
+	/**
+	 * returns an array of strings describing errors by all the script's stages
+	 *
+	 * @return array
+	 */
+	public function get_errors()
+	{
+		$all_errors = $this->_errors;
+		if (! is_array($all_errors)) {
+			$all_errors = array();
+		}
+		foreach ($this->stages() as $stage) {
+			$all_errors = array_merge($stage->get_errors(), $all_errors);
+		}
+		return $all_errors;
+	}
+
+
+	/**
+	 * Indicates whether or not this migration script should continue
+	 *
+	 * @return boolean
+	 */
+	public function can_continue()
+	{
+		return in_array(
+			$this->get_status(),
+			EE_Data_Migration_Manager::instance()->stati_that_indicate_to_continue_single_migration_script
+		);
+	}
+
+
+	/**
+	 * Gets all the data migration stages associated with this script. Note:
+	 * addons can filter this list to add their own stages, and because the list is
+	 * numerically-indexed, they can insert their stage wherever they like and it will
+	 * get ordered by the indexes
+	 *
+	 * @return EE_Data_Migration_Script_Stage[]
+	 */
+	protected function stages()
+	{
+		$stages = apply_filters('FHEE__' . get_class($this) . '__stages', $this->_migration_stages);
+		ksort($stages);
+		return $stages;
+	}
+
+
+	/**
+	 * Gets a string which should describe what's going on currently with this migration, which
+	 * can be displayed to the user
+	 *
+	 * @return string
+	 */
+	public function get_feedback_message()
+	{
+		return $this->_feedback_message;
+	}
+
+
+	/**
+	 * A lot like "__sleep()" magic method in purpose, this is meant for persisting this class'
+	 * properties to the DB. However, we don't want to use __sleep() because its quite
+	 * possible that this class is defined when it goes to sleep, but NOT available when it
+	 * awakes (eg, this class is part of an addon that is deactivated at some point).
+	 */
+	public function properties_as_array()
+	{
+		$properties = parent::properties_as_array();
+		$properties['_migration_stages'] = array();
+		foreach ($this->_migration_stages as $migration_stage_priority => $migration_stage_class) {
+			$properties['_migration_stages'][ $migration_stage_priority ] = $migration_stage_class->properties_as_array(
+			);
+		}
+		unset($properties['_mappings']);
+
+		foreach ($this->_mappings as $old_table_name => $mapping_to_new_table) {
+			foreach ($mapping_to_new_table as $new_table_name => $mapping) {
+				$this->_set_mapping_option($old_table_name, $new_table_name, $mapping);
+			}
+		}
+		return $properties;
+	}
+
+
+	/**
+	 * Sets all of the properties of this script stage to match what's in the array, which is assumed
+	 * to have been made from the properties_as_array() function.
+	 *
+	 * @param array $array_of_properties like what's produced from properties_as_array() method
+	 * @return void
+	 */
+	public function instantiate_from_array_of_properties($array_of_properties)
+	{
+		$stages_properties_arrays = $array_of_properties['_migration_stages'];
+		unset($array_of_properties['_migration_stages']);
+		unset($array_of_properties['class']);
+		foreach ($array_of_properties as $property_name => $property_value) {
+			$this->{$property_name} = $property_value;
+		}
+		// _migration_stages are already instantiated, but have only default data
+		foreach ($this->_migration_stages as $stage) {
+			$stage_data = $this->_find_migration_stage_data_with_classname(
+				get_class($stage),
+				$stages_properties_arrays
+			);
+			// SO, if we found the stage data that was saved, use it. Otherwise, I guess the stage is new? (maybe added by
+			// an addon? Unlikely... not sure why it wouldn't exist, but if it doesn't just treat it like it was never started yet)
+			if ($stage_data) {
+				$stage->instantiate_from_array_of_properties($stage_data);
+			}
+		}
+	}
+
+
+	/**
+	 * Gets the migration data from the array $migration_stage_data_arrays (which is an array of arrays, each of which
+	 * is pretty well identical to EE_Data_Migration_Stage objects except all their properties are array indexes)
+	 * for the given classname
+	 *
+	 * @param string $classname
+	 * @param array  $migration_stage_data_arrays
+	 * @return null
+	 */
+	private function _find_migration_stage_data_with_classname($classname, $migration_stage_data_arrays)
+	{
+		foreach ($migration_stage_data_arrays as $migration_stage_data_array) {
+			if (isset($migration_stage_data_array['class']) && $migration_stage_data_array['class'] == $classname) {
+				return $migration_stage_data_array;
+			}
+		}
+		return null;
+	}
+
+
+	/**
+	 * Returns the version that this script migrates to, based on the script's name.
+	 * Cannot be overwritten because lots of code needs to know which version a script
+	 * migrates to knowing only its name.
+	 *
+	 * @return array where the first key is the plugin's slug, the 2nd is the version of that plugin
+	 * that will be updated to. Eg array('Core','4.1.0')
+	 */
+	final public function migrates_to_version()
+	{
+		return EE_Data_Migration_Manager::instance()->script_migrates_to_version(get_class($this));
+	}
+
+
+	/**
+	 * Gets this addon's slug as it would appear in the current_db_state wp option,
+	 * and if this migration script is for an addon, it SHOULD match the addon's slug
+	 * (and also the addon's classname, minus the 'EE_' prefix.). Eg, 'Calendar' for the EE_Calendar addon.
+	 * Or 'Core' for core (non-addon).
+	 *
+	 * @return string
+	 */
+	public function slug()
+	{
+		$migrates_to_version_info = $this->migrates_to_version();
+		// the slug is the first part of the array
+		return $migrates_to_version_info['slug'];
+	}
+
+
+	/**
+	 * Returns the script's priority relative to DMSs from other addons. However, when
+	 * two DMSs from the same addon/core apply, this is ignored (and instead the version that
+	 * the script migrates to is used to determine which to run first). The default is 5, but all core DMSs
+	 * normally have priority 10. (So if you want a DMS "A" to run before DMS "B", both of which are from addons,
+	 * and both of which CAN run at the same time (ie, "B" doesn't depend on "A" to set
+	 * the database up so it can run), then you can set "A" to priority 3 or something.
+	 *
+	 * @return int
+	 */
+	public function priority()
+	{
+		return $this->_priority;
+	}
+
+
+	/**
+	 * Sets whether or not this DMS is being ran as part of a migration, instead of
+	 * just being used to setup (or verify) the current database structure matches
+	 * what the latest DMS indicates it should be
+	 *
+	 * @param boolean $migrating
+	 * @return void
+	 */
+	public function set_migrating($migrating = true)
+	{
+		$this->_migrating = $migrating;
+	}
+
+	/**
+	 * Marks that we think this migration class can continue to migrate
+	 */
+	public function reattempt()
+	{
+		parent::reattempt();
+		// also, we want to reattempt any stages that were marked as borked
+		foreach ($this->stages() as $stage) {
+			if ($stage->is_broken()) {
+				$stage->reattempt();
+			}
+		}
+	}
 }