# Django 2.2.9.dev20191202104323 文档

# django.contrib.postgres.operations 源代码

    from django.contrib.postgres.signals import (
        get_citext_oids, get_hstore_oids, register_type_handlers,
    )
    from django.db.migrations.operations.base import Operation

    class CreateExtension(Operation):
        reversible = True

        def __init__(self, name):
            self.name = name

        def state_forwards(self, app_label, state):
            pass

        def database_forwards(self, app_label, schema_editor, from_state, to_state):
            if schema_editor.connection.vendor != 'postgresql':
                return
            schema_editor.execute("CREATE EXTENSION IF NOT EXISTS %s" % schema_editor.quote_name(self.name))
            # Clear cached, stale oids.
            get_hstore_oids.cache_clear()
            get_citext_oids.cache_clear()
            # Registering new type handlers cannot be done before the extension is
            # installed, otherwise a subsequent data migration would use the same
            # connection.
            register_type_handlers(schema_editor.connection)

        def database_backwards(self, app_label, schema_editor, from_state, to_state):
            schema_editor.execute("DROP EXTENSION %s" % schema_editor.quote_name(self.name))
            # Clear cached, stale oids.
            get_hstore_oids.cache_clear()
            get_citext_oids.cache_clear()

        def describe(self):
            return "Creates extension %s" % self.name

    class BtreeGinExtension(CreateExtension):

        def __init__(self):
            self.name = 'btree_gin'

    class BtreeGistExtension(CreateExtension):

        def __init__(self):
            self.name = 'btree_gist'

    class CITextExtension(CreateExtension):

        def __init__(self):
            self.name = 'citext'

    class CryptoExtension(CreateExtension):

        def __init__(self):
            self.name = 'pgcrypto'

    class HStoreExtension(CreateExtension):

        def __init__(self):
            self.name = 'hstore'

    class TrigramExtension(CreateExtension):

        def __init__(self):
            self.name = 'pg_trgm'

    class UnaccentExtension(CreateExtension):

        def __init__(self):
            self.name = 'unaccent'