Loading docs/ref/schema-editor.txt +17 −0 Original line number Diff line number Diff line Loading @@ -149,3 +149,20 @@ If the database has the ``supports_combined_alters``, Django will try and do as many of these in a single database call as possible; otherwise, it will issue a separate ALTER statement for each change, but will not issue ALTERs where no change is required (as South often did). Attributes ========== All attributes should be considered read-only unless stated otherwise. connection ---------- .. attribute:: SchemaEditor.connection A connection object to the database. A useful attribute of the connection is ``alias`` which can be used to determine the name of the database being accessed. This is useful when doing data migrations for :ref:`migrations with multiple databases <data-migrations-and-multiple-databases>`. docs/topics/migrations.txt +67 −0 Original line number Diff line number Diff line Loading @@ -467,6 +467,73 @@ You can pass a second callable to want executed when migrating backwards. If this callable is omitted, migrating backwards will raise an exception. .. _data-migrations-and-multiple-databases: Data migrations and multiple databases ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When using multiple databases, you may need to figure out whether or not to run a migration against a particular database. For example, you may want to **only** run a migration on a particular database. In order to do that you can check the database connection's alias inside a ``RunPython`` operation by looking at the ``schema_editor.connection.alias`` attribute:: from django.db import migrations def forwards(apps, schema_editor): if not schema_editor.connection.alias == 'default': return # Your migration code goes here class Migration(migrations.Migration): dependencies = [ # Dependencies to other migrations ] operations = [ migrations.RunPython(forwards), ] You can also use your database router's ``allow_migrate()`` method, but keep in mind that the imported router needs to stay around as long as it is referenced inside a migration: .. snippet:: :filename: myapp/dbrouters.py class MyRouter(object): def allow_migrate(self, db, model): return db == 'default' Then, to leverage this in your migrations, do the following:: from django.db import migrations from myappname.dbrouters import MyRouter def forwards(apps, schema_editor): MyModel = apps.get_model("myappname", "MyModel") if not MyRouter().allow_migrate(schema_editor.connection.alias, MyModel): return # Your migration code goes here class Migration(migrations.Migration): dependencies = [ # Dependencies to other migrations ] operations = [ migrations.RunPython(forwards), ] More advanced migrations ~~~~~~~~~~~~~~~~~~~~~~~~ If you're interested in the more advanced migration operations, or want to be able to write your own, see the :doc:`migration operations reference </ref/migration-operations>`. Loading Loading
docs/ref/schema-editor.txt +17 −0 Original line number Diff line number Diff line Loading @@ -149,3 +149,20 @@ If the database has the ``supports_combined_alters``, Django will try and do as many of these in a single database call as possible; otherwise, it will issue a separate ALTER statement for each change, but will not issue ALTERs where no change is required (as South often did). Attributes ========== All attributes should be considered read-only unless stated otherwise. connection ---------- .. attribute:: SchemaEditor.connection A connection object to the database. A useful attribute of the connection is ``alias`` which can be used to determine the name of the database being accessed. This is useful when doing data migrations for :ref:`migrations with multiple databases <data-migrations-and-multiple-databases>`.
docs/topics/migrations.txt +67 −0 Original line number Diff line number Diff line Loading @@ -467,6 +467,73 @@ You can pass a second callable to want executed when migrating backwards. If this callable is omitted, migrating backwards will raise an exception. .. _data-migrations-and-multiple-databases: Data migrations and multiple databases ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When using multiple databases, you may need to figure out whether or not to run a migration against a particular database. For example, you may want to **only** run a migration on a particular database. In order to do that you can check the database connection's alias inside a ``RunPython`` operation by looking at the ``schema_editor.connection.alias`` attribute:: from django.db import migrations def forwards(apps, schema_editor): if not schema_editor.connection.alias == 'default': return # Your migration code goes here class Migration(migrations.Migration): dependencies = [ # Dependencies to other migrations ] operations = [ migrations.RunPython(forwards), ] You can also use your database router's ``allow_migrate()`` method, but keep in mind that the imported router needs to stay around as long as it is referenced inside a migration: .. snippet:: :filename: myapp/dbrouters.py class MyRouter(object): def allow_migrate(self, db, model): return db == 'default' Then, to leverage this in your migrations, do the following:: from django.db import migrations from myappname.dbrouters import MyRouter def forwards(apps, schema_editor): MyModel = apps.get_model("myappname", "MyModel") if not MyRouter().allow_migrate(schema_editor.connection.alias, MyModel): return # Your migration code goes here class Migration(migrations.Migration): dependencies = [ # Dependencies to other migrations ] operations = [ migrations.RunPython(forwards), ] More advanced migrations ~~~~~~~~~~~~~~~~~~~~~~~~ If you're interested in the more advanced migration operations, or want to be able to write your own, see the :doc:`migration operations reference </ref/migration-operations>`. Loading
