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<?php |
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/** |
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* |
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* This file is part of Aura for PHP. |
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* |
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* @license http://opensource.org/licenses/mit-license.php MIT |
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* |
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*/ |
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namespace Aura\SqlQuery; |
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/** |
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* |
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* Creates query statement objects. |
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* |
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* @package Aura.SqlQuery |
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* |
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*/ |
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class QueryFactory |
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{ |
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/** |
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* Use the 'common' driver instead of a database-specific one. |
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*/ |
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const COMMON = 'common'; |
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/** |
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* |
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* What database are we building for? |
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* |
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* @param string |
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* |
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*/ |
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protected $db; |
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/** |
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* |
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* Build "common" query objects regardless of database type? |
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* |
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* @param bool |
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* |
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*/ |
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protected $common = false; |
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/** |
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* |
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* A map of `table.col` names to last-insert-id names. |
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* |
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* @var array |
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* |
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*/ |
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protected $last_insert_id_names = array(); |
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/** |
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* |
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* A Quoter for identifiers. |
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* @param QuoterInterface |
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* |
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*/ |
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protected $quoter; |
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protected $instance_count = 0; |
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/** |
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* |
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* Constructor. |
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* |
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* @param string $db The database type. |
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* |
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* @param string $common Pass the constant self::COMMON to force common |
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* query objects instead of db-specific ones. |
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* |
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*/ |
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public function __construct($db, $common = null) |
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{ |
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$this->db = ucfirst(strtolower($db)); |
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$this->common = ($common === self::COMMON); |
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} |
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/** |
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* |
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* Sets the last-insert-id names to be used for Insert queries.. |
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* |
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* @param array $last_insert_id_names A map of `table.col` names to |
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* last-insert-id names. |
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* |
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* @return null |
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* |
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*/ |
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public function setLastInsertIdNames(array $last_insert_id_names) |
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{ |
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$this->last_insert_id_names = $last_insert_id_names; |
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} |
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/** |
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* |
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* Returns a new SELECT object. |
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* @return Common\SelectInterface |
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* |
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*/ |
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public function newSelect() |
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{ |
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return $this->newInstance('Select'); |
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} |
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/** |
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* |
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* Returns a new INSERT object. |
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* @return Common\InsertInterface |
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*/ |
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public function newInsert() |
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{ |
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$insert = $this->newInstance('Insert'); |
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$insert->setLastInsertIdNames($this->last_insert_id_names); |
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return $insert; |
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} |
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/** |
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* |
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* Returns a new UPDATE object. |
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* |
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* @return Common\UpdateInterface |
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* |
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*/ |
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public function newUpdate() |
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{ |
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return $this->newInstance('Update'); |
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} |
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/** |
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* |
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* Returns a new DELETE object. |
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* @return Common\DeleteInterface |
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* |
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*/ |
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public function newDelete() |
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{ |
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return $this->newInstance('Delete'); |
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} |
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/** |
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* |
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* Returns a new query object. |
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* |
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* @param string $query The query object type. |
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* |
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* @return Common\SelectInterface|Common\InsertInterface|Common\UpdateInterface|Common\DeleteInterface |
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* |
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*/ |
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protected function newInstance($query) |
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{ |
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$queryClass = "Aura\SqlQuery\\{$this->db}\\{$query}"; |
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if ($this->common) { |
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$queryClass = "Aura\SqlQuery\Common\\{$query}"; |
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} |
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$builderClass = "Aura\SqlQuery\\{$this->db}\\{$query}Builder"; |
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if ($this->common || ! class_exists($builderClass)) { |
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$builderClass = "Aura\SqlQuery\Common\\{$query}Builder"; |
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} |
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return new $queryClass( |
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$this->getQuoter(), |
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$this->newBuilder($query), |
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$this->getSeqBindPrefix() |
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); |
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} |
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protected function getSeqBindPrefix() |
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{ |
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$seq_bind_prefix = ''; |
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if ($this->instance_count > 0) { |
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$seq_bind_prefix = '_' . $this->instance_count; |
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} |
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$this->instance_count ++; |
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return $seq_bind_prefix; |
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} |
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/** |
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* |
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* Returns a new Builder for the database driver. |
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* @param string $query The query type. |
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* |
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* @return AbstractBuilder |
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*/ |
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protected function newBuilder($query) |
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{ |
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$builderClass = "Aura\SqlQuery\\{$this->db}\\{$query}Builder"; |
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if ($this->common || ! class_exists($builderClass)) { |
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$builderClass = "Aura\SqlQuery\Common\\{$query}Builder"; |
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} |
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return new $builderClass(); |
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} |
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/** |
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* |
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* Returns the Quoter object for queries; creates one if needed. |
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* |
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* @return Quoter |
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* |
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*/ |
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protected function getQuoter() |
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{ |
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if (! $this->quoter) { |
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$this->quoter = $this->newQuoter(); |
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} |
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return $this->quoter; |
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} |
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/** |
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* |
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* Returns a new Quoter for the database driver. |
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* |
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* @return QuoterInerface |
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* |
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*/ |
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protected function newQuoter() |
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{ |
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$quoterClass = "Aura\SqlQuery\\{$this->db}\Quoter"; |
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if (! class_exists($quoterClass)) { |
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$quoterClass = "Aura\SqlQuery\Common\Quoter"; |
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} |
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return new $quoterClass(); |
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} |
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} |
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If you return a value from a function or method, it should be a sub-type of the type that is given by the parent type f.e. an interface, or abstract method. This is more formally defined by the Lizkov substitution principle, and guarantees that classes that depend on the parent type can use any instance of a child type interchangably. This principle also belongs to the SOLID principles for object oriented design.
Let’s take a look at an example:
Our function
my_function
expects aPost
object, and outputs the author of the post. The base classPost
returns a simple string and outputting a simple string will work just fine. However, the child classBlogPost
which is a sub-type ofPost
instead decided to return anobject
, and is therefore violating the SOLID principles. If aBlogPost
were passed tomy_function
, PHP would not complain, but ultimately fail when executing thestrtoupper
call in its body.