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import importlib |
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from django.conf import settings |
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from django.core.exceptions import ImproperlyConfigured |
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from django.db.backends.postgresql.base import \ |
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DatabaseWrapper as Psycopg2DatabaseWrapper |
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def _get_backend_base(): |
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"""Gets the base class for the custom database back-end. |
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This should be the Django PostgreSQL back-end. However, |
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some people are already using a custom back-end from |
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another package. We are nice people and expose an option |
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that allows them to configure the back-end we base upon. |
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As long as the specified base eventually also has |
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the PostgreSQL back-end as a base, then everything should |
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work as intended. |
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""" |
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base_class_name = getattr( |
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settings, |
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'LOCALIZED_FIELDS_DB_BACKEND_BASE', |
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'django.db.backends.postgresql' |
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) |
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base_class_module = importlib.import_module(base_class_name + '.base') |
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base_class = getattr(base_class_module, 'DatabaseWrapper', None) |
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if not base_class: |
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raise ImproperlyConfigured(( |
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'\'%s\' is not a valid database back-end.' |
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' The module does not define a DatabaseWrapper class.' |
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' Check the value of LOCALIZED_FIELDS_DB_BACKEND_BASE.' |
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)) |
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if isinstance(base_class, Psycopg2DatabaseWrapper): |
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raise ImproperlyConfigured(( |
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'\'%s\' is not a valid database back-end.' |
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' It does inherit from the PostgreSQL back-end.' |
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' Check the value of LOCALIZED_FIELDS_DB_BACKEND_BASE.' |
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)) |
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return base_class |
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def _get_schema_editor_base(): |
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"""Gets the base class for the schema editor. |
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We have to use the configured base back-end's |
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schema editor for this.""" |
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return _get_backend_base().SchemaEditorClass |
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class SchemaEditor(_get_schema_editor_base()): |
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"""Custom schema editor for hstore indexes. |
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This allows us to put UNIQUE constraints for |
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localized fields.""" |
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sql_hstore_unique_create = "CREATE UNIQUE INDEX {name} ON {table}{using} ({columns}){extra}" |
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sql_hstore_unique_drop = "DROP INDEX IF EXISTS {name}" |
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@staticmethod |
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def _hstore_unique_name(model, field, keys): |
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"""Gets the name for a UNIQUE INDEX that applies |
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to one or more keys in a hstore field. |
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Arguments: |
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model: |
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The model the field is a part of. |
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field: |
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The hstore field to create a |
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UNIQUE INDEX for. |
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key: |
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The name of the hstore key |
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to create the name for. |
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This can also be a tuple |
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of multiple names. |
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Returns: |
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The name for the UNIQUE index. |
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""" |
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postfix = '_'.join(keys) |
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return '{table_name}_{field_name}_unique_{postfix}'.format( |
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table_name=model._meta.db_table, |
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field_name=field.column, |
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postfix=postfix |
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) |
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def _drop_hstore_unique(self, model, field, keys): |
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"""Drops a UNIQUE constraint for the specified hstore keys.""" |
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name = self._hstore_unique_name(model, field, keys) |
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sql = self.sql_hstore_unique_drop.format(name=name) |
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self.execute(sql) |
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def _create_hstore_unique(self, model, field, keys): |
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"""Creates a UNIQUE constraint for the specified hstore keys.""" |
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name = self._hstore_unique_name(model, field, keys) |
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columns = [ |
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'(%s->\'%s\')' % (field.column, key) |
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for key in keys |
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] |
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sql = self.sql_hstore_unique_create.format( |
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name=name, |
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table=model._meta.db_table, |
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using='', |
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columns=','.join(columns), |
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extra='' |
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) |
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self.execute(sql) |
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def _update_hstore_constraints(self, model, old_field, new_field): |
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"""Updates the UNIQUE constraints for the specified field.""" |
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old_uniqueness = getattr(old_field, 'uniqueness', None) |
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new_uniqueness = getattr(new_field, 'uniqueness', None) |
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def _compose_keys(constraint): |
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if isinstance(constraint, str): |
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return [constraint] |
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return constraint |
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# drop any old uniqueness constraints |
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if old_uniqueness: |
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for keys in old_uniqueness: |
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self._drop_hstore_unique( |
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model, |
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old_field, |
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_compose_keys(keys) |
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) |
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# (re-)create uniqueness constraints |
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if new_uniqueness: |
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for keys in new_uniqueness: |
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self._create_hstore_unique( |
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model, |
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old_field, |
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_compose_keys(keys) |
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) |
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def _alter_field(self, model, old_field, new_field, *args, **kwargs): |
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"""Ran when the configuration on a field changed.""" |
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super()._alter_field( |
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model, old_field, new_field, |
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*args, **kwargs |
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) |
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self._update_hstore_constraints(model, old_field, new_field) |
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class DatabaseWrapper(_get_backend_base()): |
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"""Wraps the standard PostgreSQL database back-end. |
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Overrides the schema editor with our custom |
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schema editor and makes sure the `hstore` |
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extension is enabled.""" |
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SchemaEditorClass = SchemaEditor |
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def prepare_database(self): |
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"""Ran to prepare the configured database. |
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This is where we enable the `hstore` extension |
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if it wasn't enabled yet.""" |
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super().prepare_database() |
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with self.cursor() as cursor: |
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cursor.execute('CREATE EXTENSION IF NOT EXISTS hstore') |
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SectorLabs /
django-localized-fields
