From 6f3813e4b6e3db7fa3cc612c78f898142468bca9 Mon Sep 17 00:00:00 2001 From: Samriddha9619 Date: Tue, 23 Sep 2025 01:27:30 +0530 Subject: [PATCH] [5.2.x] Fixed #35877, Refs #36128 -- Documented unique constraint when migrating a m2m field to use a through model. Backport of daba609a9bdc7a97bcf327c7ba0a5f7b3540b46e from main. --- docs/howto/writing-migrations.txt | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/docs/howto/writing-migrations.txt b/docs/howto/writing-migrations.txt index 2c52eccbad..34052805bc 100644 --- a/docs/howto/writing-migrations.txt +++ b/docs/howto/writing-migrations.txt @@ -334,7 +334,7 @@ model, the default migration will delete the existing table and create a new one, losing the existing relations. To avoid this, you can use :class:`.SeparateDatabaseAndState` to rename the existing table to the new table name while telling the migration autodetector that the new model has -been created. You can check the existing table name through +been created. You can check the existing table name and constraint name through :djadmin:`sqlmigrate` or :djadmin:`dbshell`. You can check the new table name with the through model's ``_meta.db_table`` property. Your new ``through`` model should use the same names for the ``ForeignKey``\s as Django did. Also if @@ -392,6 +392,14 @@ For example, if we had a ``Book`` model with a ``ManyToManyField`` linking to ), ), ], + options={ + "constraints": [ + models.UniqueConstraint( + fields=["author", "book"], + name="unique_author_book", + ) + ], + }, ), migrations.AlterField( model_name="book",