From 4283a038431ef6428d086d4911179bd8eb8b2299 Mon Sep 17 00:00:00 2001 From: Bibhas Date: Wed, 9 Sep 2015 15:56:09 +0530 Subject: [PATCH] Fixed #25371 -- Added reverse_sql and reverse_code examples to docs. --- docs/ref/migration-operations.txt | 24 +++++++++++++++++++++--- 1 file changed, 21 insertions(+), 3 deletions(-) diff --git a/docs/ref/migration-operations.txt b/docs/ref/migration-operations.txt index 8dbebcccc6..980c736b3d 100644 --- a/docs/ref/migration-operations.txt +++ b/docs/ref/migration-operations.txt @@ -224,6 +224,14 @@ queries and parameters in the same way as :ref:`cursor.execute() If you want to include literal percent signs in the query, you have to double them if you are passing parameters. +The ``reverse_sql`` queries are executed when the migration is unapplied, so +you can reverse the changes done in the forwards queries:: + + migrations.RunSQL( + ["INSERT INTO musician (name) VALUES (%s);", ['Reinhardt']], + ["DELETE FROM musician where name=%s;", ['Reinhardt']], + ) + The ``state_operations`` argument is so you can supply operations that are equivalent to the SQL in terms of project state; for example, if you are manually creating a column, you should pass in a list containing an ``AddField`` @@ -265,6 +273,10 @@ match the operation's place in the project history, and the second is an instance of :class:`SchemaEditor `. +The ``reverse_code`` argument is called when unapplying migrations. This +callable should undo what is done in the ``code`` callable so that the +migration is reversible. + The optional ``hints`` argument will be passed as ``**hints`` to the :meth:`allow_migrate` method of database routers to assist them in making a routing decision. See :ref:`topics-db-multi-db-hints` for more details on @@ -294,14 +306,20 @@ model:: Country(name="France", code="fr"), ]) + def reverse_func(apps, schema_editor): + # forwards_func() creates two Country instances, + # so reverse_func() should delete them. + Country = apps.get_model("myapp", "Country") + db_alias = schema_editor.connection.alias + Country.objects.using(db_alias).filter(name="USA", code="us").delete() + Country.objects.using(db_alias).filter(name="France", code="fr").delete() + class Migration(migrations.Migration): dependencies = [] operations = [ - migrations.RunPython( - forwards_func, - ), + migrations.RunPython(forwards_func, reverse_func), ] This is generally the operation you would use to create