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

Backport of 4bb859e246 from master.

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
 

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):

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):