# Τεκμηρίωση του Django - 1.10.7

# Πηγαίος κώδικας για το django.contrib.postgres.operations

    from django.contrib.postgres.signals import register_hstore_handler
    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))

        def database_backwards(self, app_label, schema_editor, from_state, to_state):
            schema_editor.execute("DROP EXTENSION %s" % schema_editor.quote_name(self.name))

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

    class HStoreExtension(CreateExtension):

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

        def database_forwards(self, app_label, schema_editor, from_state, to_state):
            super(HStoreExtension, self).database_forwards(app_label, schema_editor, from_state, to_state)
            # Register hstore straight away as it cannot be done before the
            # extension is installed, a subsequent data migration would use the
            # same connection
            register_hstore_handler(schema_editor.connection)

    class UnaccentExtension(CreateExtension):

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

    class TrigramExtension(CreateExtension):

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