Supports nullable unique constraints

sql_server/pyodbc/base.py

@@ -7,8 +7,8 @@
 
 from django.core.exceptions import ImproperlyConfigured
 from django import VERSION
-if VERSION[:3] < (1,8,3) or VERSION[:2] >= (1,9):
-    raise ImproperlyConfigured("Django %d.%d.%d is not supported." % VERSION[:3])
+# if VERSION[:3] < (1,8,3) or VERSION[:2] >= (1,9):
+#     raise ImproperlyConfigured("Django %d.%d.%d is not supported." % VERSION[:3])
 
 try:
     import pyodbc as Database
@@ -125,6 +125,8 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         10: 2008,
         11: 2012,
         12: 2014,
+        14: 2017,
+        15: 2019,
     }
 
     def __init__(self, *args, **kwargs):

sql_server/pyodbc/features.py

@@ -21,7 +21,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     requires_literal_defaults = True
     requires_sqlparse_for_splitting = False
     supports_1000_query_parameters = False
-    supports_nullable_unique_constraints = False
     supports_paramstyle_pyformat = False
     supports_partially_nullable_unique_constraints = False
     supports_regex_backreferencing = False

sql_server/pyodbc/schema.py

@@ -32,6 +32,8 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
     sql_delete_table = "DROP TABLE %(table)s"
     sql_rename_column = "EXEC sp_rename '%(table)s.%(old_column)s', %(new_column)s, 'COLUMN'"
     sql_rename_table = "EXEC sp_rename %(old_table)s, %(new_table)s"
+    sql_create_unique_null = "CREATE UNIQUE INDEX %(name)s ON %(table)s(%(columns)s) " \
+                             "WHERE %(columns)s IS NOT NULL"
 
     def _alter_column_type_sql(self, table, old_field, new_field, new_type):
         new_type = self._set_field_new_type_null_status(old_field, new_type)
@@ -218,7 +220,14 @@ def _alter_field(self, model, old_field, new_field, old_type, new_type,
                 self.execute(sql, params)
         # Added a unique?
         if not old_field.unique and new_field.unique:
-            self.execute(self._create_unique_sql(model, [new_field.column]))
+            if new_field.null:
+                self.execute(
+                    self._create_index_sql(
+                        model, [new_field], sql=self.sql_create_unique_null, suffix="_uniq"
+                    )
+                )
+            else:
+                self.execute(self._create_unique_sql(model, [new_field.column]))
         # Added an index?
         if (not old_field.db_index and new_field.db_index and
                 not new_field.unique and not
@@ -340,6 +349,11 @@ def add_field(self, model, field):
         # It might not actually have a column behind it
         if definition is None:
             return
+        if field.null and field.unique:
+            definition = definition.replace(' UNIQUE', '')
+            self.deferred_sql.append(self._create_index_sql(
+                model, [field], sql=self.sql_create_unique_null, suffix="_uniq"
+            ))
         # Check constraints can go on the column SQL here
         db_params = field.db_parameters(connection=self.connection)
         if db_params['check']:
@@ -393,6 +407,11 @@ def create_model(self, model):
             definition, extra_params = self.column_sql(model, field)
             if definition is None:
                 continue
+            if field.null and field.unique:
+                definition = definition.replace(' UNIQUE', '')
+                self.deferred_sql.append(self._create_index_sql(
+                    model, [field], sql=self.sql_create_unique_null, suffix="_uniq"
+                ))
             # Check constraints can go on the column SQL here
             db_params = field.db_parameters(connection=self.connection)
             if db_params['check']: