Fixed #25492 -- Checked deferred foreign key constraints before dropping them.

This allows running foreign key data and schema altering operations in the
same migration on PostgreSQL.

Thanks Tim for review.

1 files changed, 4 insertions, 0 deletions

diff --git a/django/db/backends/postgresql/schema.py b/django/db/backends/postgresql/schema.py
index 1afb85d468..bffa8bd45b 100644
--- a/django/db/backends/postgresql/schema.py
+++ b/django/db/backends/postgresql/schema.py
@@ -15,6 +15,10 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
     sql_create_varchar_index = "CREATE INDEX %(name)s ON %(table)s (%(columns)s varchar_pattern_ops)%(extra)s"
     sql_create_text_index = "CREATE INDEX %(name)s ON %(table)s (%(columns)s text_pattern_ops)%(extra)s"
 
+    # Setting the constraint to IMMEDIATE runs any deferred checks to allow
+    # dropping it in the same transaction.
+    sql_delete_fk = "SET CONSTRAINTS %(name)s IMMEDIATE; ALTER TABLE %(table)s DROP CONSTRAINT %(name)s"
+
     def quote_value(self, value):
         return psycopg2.extensions.adapt(value)