[2.2.x] Refs #30172 -- Prevented removing a field's check or unique constraint from removing Meta constraints.

Backport of 4bb859e24694f6cb8974ed9d2225f18214338ea3 from master.

5 files changed, 125 insertions, 8 deletions

diff --git a/django/db/backends/base/features.py b/django/db/backends/base/features.py
index 8afc7eb516..99ab45f21c 100644
--- a/django/db/backends/base/features.py
+++ b/django/db/backends/base/features.py
@@ -281,6 +281,10 @@ class BaseDatabaseFeatures:
     supports_partial_indexes = True
     supports_functions_in_partial_indexes = True
 
+    # Does the database allow more than one constraint or index on the same
+    # field(s)?
+    allows_multiple_constraints_on_same_fields = True
+
     def __init__(self, connection):
         self.connection = connection
 
diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index 113d1b7f67..19c9a04ba8 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -548,7 +548,11 @@ class BaseDatabaseSchemaEditor:
         # Has unique been removed?
         if old_field.unique and (not new_field.unique or self._field_became_primary_key(old_field, new_field)):
             # Find the unique constraint for this field
-            constraint_names = self._constraint_names(model, [old_field.column], unique=True, primary_key=False)
+            meta_constraint_names = {constraint.name for constraint in model._meta.constraints}
+            constraint_names = self._constraint_names(
+                model, [old_field.column], unique=True, primary_key=False,
+                exclude=meta_constraint_names,
+            )
             if strict and len(constraint_names) != 1:
                 raise ValueError("Found wrong number (%s) of unique constraints for %s.%s" % (
                     len(constraint_names),
@@ -598,7 +602,11 @@ class BaseDatabaseSchemaEditor:
                     self.execute(self._delete_index_sql(model, index_name))
         # Change check constraints?
         if old_db_params['check'] != new_db_params['check'] and old_db_params['check']:
-            constraint_names = self._constraint_names(model, [old_field.column], check=True)
+            meta_constraint_names = {constraint.name for constraint in model._meta.constraints}
+            constraint_names = self._constraint_names(
+                model, [old_field.column], check=True,
+                exclude=meta_constraint_names,
+            )
             if strict and len(constraint_names) != 1:
                 raise ValueError("Found wrong number (%s) of check constraints for %s.%s" % (
                     len(constraint_names),
@@ -1089,7 +1097,7 @@ class BaseDatabaseSchemaEditor:
 
     def _constraint_names(self, model, column_names=None, unique=None,
                           primary_key=None, index=None, foreign_key=None,
-                          check=None, type_=None):
+                          check=None, type_=None, exclude=None):
         """Return all constraint names matching the columns and conditions."""
         if column_names is not None:
             column_names = [
@@ -1113,7 +1121,8 @@ class BaseDatabaseSchemaEditor:
                     continue
                 if type_ is not None and infodict['type'] != type_:
                     continue
-                result.append(name)
+                if not exclude or name not in exclude:
+                    result.append(name)
         return result
 
     def _delete_primary_key(self, model, strict=False):
diff --git a/django/db/backends/oracle/features.py b/django/db/backends/oracle/features.py
index ec301d9d37..55bf327440 100644
--- a/django/db/backends/oracle/features.py
+++ b/django/db/backends/oracle/features.py
@@ -56,6 +56,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_ignore_conflicts = False
     max_query_params = 2**16 - 1
     supports_partial_indexes = False
+    allows_multiple_constraints_on_same_fields = False
 
     @cached_property
     def has_fetch_offset_support(self):
diff --git a/tests/schema/models.py b/tests/schema/models.py
index f6bdbd8815..2c277c681b 100644
--- a/tests/schema/models.py
+++ b/tests/schema/models.py
@@ -55,6 +55,13 @@ class AuthorWithIndexedName(models.Model):
         apps = new_apps
 
 
+class AuthorWithUniqueName(models.Model):
+    name = models.CharField(max_length=255, unique=True)
+
+    class Meta:
+        apps = new_apps
+
+
 class Book(models.Model):
     author = models.ForeignKey(Author, models.CASCADE)
     title = models.CharField(max_length=100, db_index=True)
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index 37f39ff7ed..6bcf3b5563 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -7,7 +7,8 @@ from unittest import mock
 from django.db import (
     DatabaseError, IntegrityError, OperationalError, connection,
 )
-from django.db.models import Model
+from django.db.models import Model, Q
+from django.db.models.constraints import CheckConstraint, UniqueConstraint
 from django.db.models.deletion import CASCADE, PROTECT
 from django.db.models.fields import (
     AutoField, BigAutoField, BigIntegerField, BinaryField, BooleanField,
@@ -31,9 +32,10 @@ from .fields import (
 from .models import (
     Author, AuthorCharFieldWithIndex, AuthorTextFieldWithIndex,
     AuthorWithDefaultHeight, AuthorWithEvenLongerName, AuthorWithIndexedName,
-    Book, BookForeignObj, BookWeak, BookWithLongName, BookWithO2O,
-    BookWithoutAuthor, BookWithSlug, IntegerPK, Node, Note, NoteRename, Tag,
-    TagIndexed, TagM2MTest, TagUniqueRename, Thing, UniqueTest, new_apps,
+    AuthorWithUniqueName, Book, BookForeignObj, BookWeak, BookWithLongName,
+    BookWithO2O, BookWithoutAuthor, BookWithSlug, IntegerPK, Node, Note,
+    NoteRename, Tag, TagIndexed, TagM2MTest, TagUniqueRename, Thing,
+    UniqueTest, new_apps,
 )
 
 
@@ -1524,6 +1526,53 @@ class SchemaTests(TransactionTestCase):
         if not any(details['columns'] == ['height'] and details['check'] for details in constraints.values()):
             self.fail("No check constraint for height found")
 
+    @skipUnlessDBFeature('supports_column_check_constraints')
+    def test_remove_field_check_does_not_remove_meta_constraints(self):
+        with connection.schema_editor() as editor:
+            editor.create_model(Author)
+        # Add the custom check constraint
+        constraint = CheckConstraint(check=Q(height__gte=0), name='author_height_gte_0_check')
+        custom_constraint_name = constraint.name
+        Author._meta.constraints = [constraint]
+        with connection.schema_editor() as editor:
+            editor.add_constraint(Author, constraint)
+        # Ensure the constraints exist
+        constraints = self.get_constraints(Author._meta.db_table)
+        self.assertIn(custom_constraint_name, constraints)
+        other_constraints = [
+            name for name, details in constraints.items()
+            if details['columns'] == ['height'] and details['check'] and name != custom_constraint_name
+        ]
+        self.assertEqual(len(other_constraints), 1)
+        # Alter the column to remove field check
+        old_field = Author._meta.get_field('height')
+        new_field = IntegerField(null=True, blank=True)
+        new_field.set_attributes_from_name('height')
+        with connection.schema_editor() as editor:
+            editor.alter_field(Author, old_field, new_field, strict=True)
+        constraints = self.get_constraints(Author._meta.db_table)
+        self.assertIn(custom_constraint_name, constraints)
+        other_constraints = [
+            name for name, details in constraints.items()
+            if details['columns'] == ['height'] and details['check'] and name != custom_constraint_name
+        ]
+        self.assertEqual(len(other_constraints), 0)
+        # Alter the column to re-add field check
+        new_field2 = Author._meta.get_field('height')
+        with connection.schema_editor() as editor:
+            editor.alter_field(Author, new_field, new_field2, strict=True)
+        constraints = self.get_constraints(Author._meta.db_table)
+        self.assertIn(custom_constraint_name, constraints)
+        other_constraints = [
+            name for name, details in constraints.items()
+            if details['columns'] == ['height'] and details['check'] and name != custom_constraint_name
+        ]
+        self.assertEqual(len(other_constraints), 1)
+        # Drop the check constraint
+        with connection.schema_editor() as editor:
+            Author._meta.constraints = []
+            editor.remove_constraint(Author, constraint)
+
     def test_unique(self):
         """
         Tests removing and adding unique constraints to a single column.
@@ -1650,6 +1699,53 @@ class SchemaTests(TransactionTestCase):
         with self.assertRaises(IntegrityError):
             Tag.objects.create(title='bar', slug='foo')
 
+    @skipUnlessDBFeature('allows_multiple_constraints_on_same_fields')
+    def test_remove_field_unique_does_not_remove_meta_constraints(self):
+        with connection.schema_editor() as editor:
+            editor.create_model(AuthorWithUniqueName)
+        # Add the custom unique constraint
+        constraint = UniqueConstraint(fields=['name'], name='author_name_uniq')
+        custom_constraint_name = constraint.name
+        AuthorWithUniqueName._meta.constraints = [constraint]
+        with connection.schema_editor() as editor:
+            editor.add_constraint(AuthorWithUniqueName, constraint)
+        # Ensure the constraints exist
+        constraints = self.get_constraints(AuthorWithUniqueName._meta.db_table)
+        self.assertIn(custom_constraint_name, constraints)
+        other_constraints = [
+            name for name, details in constraints.items()
+            if details['columns'] == ['name'] and details['unique'] and name != custom_constraint_name
+        ]
+        self.assertEqual(len(other_constraints), 1)
+        # Alter the column to remove field uniqueness
+        old_field = AuthorWithUniqueName._meta.get_field('name')
+        new_field = CharField(max_length=255)
+        new_field.set_attributes_from_name('name')
+        with connection.schema_editor() as editor:
+            editor.alter_field(AuthorWithUniqueName, old_field, new_field, strict=True)
+        constraints = self.get_constraints(AuthorWithUniqueName._meta.db_table)
+        self.assertIn(custom_constraint_name, constraints)
+        other_constraints = [
+            name for name, details in constraints.items()
+            if details['columns'] == ['name'] and details['unique'] and name != custom_constraint_name
+        ]
+        self.assertEqual(len(other_constraints), 0)
+        # Alter the column to re-add field uniqueness
+        new_field2 = AuthorWithUniqueName._meta.get_field('name')
+        with connection.schema_editor() as editor:
+            editor.alter_field(AuthorWithUniqueName, new_field, new_field2, strict=True)
+        constraints = self.get_constraints(AuthorWithUniqueName._meta.db_table)
+        self.assertIn(custom_constraint_name, constraints)
+        other_constraints = [
+            name for name, details in constraints.items()
+            if details['columns'] == ['name'] and details['unique'] and name != custom_constraint_name
+        ]
+        self.assertEqual(len(other_constraints), 1)
+        # Drop the unique constraint
+        with connection.schema_editor() as editor:
+            AuthorWithUniqueName._meta.constraints = []
+            editor.remove_constraint(AuthorWithUniqueName, constraint)
+
     def test_unique_together(self):
         """
         Tests removing and adding unique_together constraints on a model.