Delete deferred unique index creation when already created in the same migration

Author: ivissani

sql_server/pyodbc/schema.py

@@ -18,6 +18,8 @@
 from django.db.transaction import TransactionManagementError
 from django.utils.encoding import force_str
 
+from collections import defaultdict
+
 
 class Statement(DjStatement):
     def __hash__(self):
@@ -68,6 +70,8 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
     sql_create_unique_null = "CREATE UNIQUE INDEX %(name)s ON %(table)s(%(columns)s) " \
                              "WHERE %(columns)s IS NOT NULL"
 
+    _deferred_unique_indexes = defaultdict(list)
+
     def _alter_column_default_sql(self, model, old_field, new_field, drop=False):
         """
         Hook to specialize column default alteration.
@@ -236,6 +240,12 @@ def alter_db_table(self, model, old_db_table, new_db_table):
 
         return super().alter_db_table(model, old_db_table, new_db_table)
 
+    def _delete_deferred_unique_indexes_for_field(self, field_name):
+        deferred_statements = self._deferred_unique_indexes.get(field_name, [])
+        for stmt in deferred_statements:
+            if stmt in self.deferred_sql:
+                self.deferred_sql.remove(stmt)
+
     def _alter_field(self, model, old_field, new_field, old_type, new_type,
                      old_db_params, new_db_params, strict=False):
         """Actually perform a "physical" (non-ManyToMany) field update."""
@@ -449,6 +459,7 @@ def _alter_field(self, model, old_field, new_field, old_type, new_type,
                 )
             else:
                 self.execute(self._create_unique_sql(model, [new_field.column]))
+            self._delete_deferred_unique_indexes_for_field(old_field)
         # Added an index?
         # constraint will no longer be used in lieu of an index. The following
         # lines from the truth table show all True cases; the rest are False:
@@ -477,6 +488,7 @@ def _alter_field(self, model, old_field, new_field, old_type, new_type,
                     )
                 else:
                     self.execute(self._create_unique_sql(model, columns=[old_field.column]))
+                self._delete_deferred_unique_indexes_for_field(old_field)
             else:
                 for fields in model._meta.unique_together:
                     columns = [model._meta.get_field(field).column for field in fields]
@@ -644,9 +656,11 @@ def add_field(self, model, field):
                 not field.many_to_many and field.null and field.unique):
 
             definition = definition.replace(' UNIQUE', '')
-            self.deferred_sql.append(self._create_index_sql(
+            statement = self._create_index_sql(
                 model, [field], sql=self.sql_create_unique_null, suffix="_uniq"
-            ))
+            )
+            self.deferred_sql.append(statement)
+            self._deferred_unique_indexes[field].append(statement)
 
         # Check constraints can go on the column SQL here
         db_params = field.db_parameters(connection=self.connection)
@@ -750,9 +764,11 @@ def create_model(self, model):
                     not field.many_to_many and field.null and field.unique):
 
                 definition = definition.replace(' UNIQUE', '')
-                self.deferred_sql.append(self._create_index_sql(
+                statement = self._create_index_sql(
                     model, [field], sql=self.sql_create_unique_null, suffix="_uniq"
-                ))
+                )
+                self.deferred_sql.append(statement)
+                self._deferred_unique_indexes[field].append(statement)
 
             # Check constraints can go on the column SQL here
             db_params = field.db_parameters(connection=self.connection)