Fixed #27062 -- Eased implementing select_for_update() on MSSQL.

1 files changed, 21 insertions, 16 deletions

diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index 5eaac1fc74..7c40fbeb38 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -402,6 +402,25 @@ class SQLCompiler(object):
             result.extend(from_)
             params.extend(f_params)
 
+            for_update_part = None
+            if self.query.select_for_update and self.connection.features.has_select_for_update:
+                if self.connection.get_autocommit():
+                    raise TransactionManagementError("select_for_update cannot be used outside of a transaction.")
+
+                nowait = self.query.select_for_update_nowait
+                skip_locked = self.query.select_for_update_skip_locked
+                # If it's a NOWAIT/SKIP LOCKED query but the backend doesn't
+                # support it, raise a DatabaseError to prevent a possible
+                # deadlock.
+                if nowait and not self.connection.features.has_select_for_update_nowait:
+                    raise DatabaseError('NOWAIT is not supported on this database backend.')
+                elif skip_locked and not self.connection.features.has_select_for_update_skip_locked:
+                    raise DatabaseError('SKIP LOCKED is not supported on this database backend.')
+                for_update_part = self.connection.ops.for_update_sql(nowait=nowait, skip_locked=skip_locked)
+
+            if for_update_part and self.connection.features.for_update_after_from:
+                result.append(for_update_part)
+
             if where:
                 result.append('WHERE %s' % where)
                 params.extend(w_params)
@@ -439,22 +458,8 @@ class SQLCompiler(object):
                             result.append('LIMIT %d' % val)
                     result.append('OFFSET %d' % self.query.low_mark)
 
-            if self.query.select_for_update and self.connection.features.has_select_for_update:
-                if self.connection.get_autocommit():
-                    raise TransactionManagementError(
-                        "select_for_update cannot be used outside of a transaction."
-                    )
-
-                nowait = self.query.select_for_update_nowait
-                skip_locked = self.query.select_for_update_skip_locked
-                # If we've been asked for a NOWAIT/SKIP LOCKED query but the
-                # backend does not support it, raise a DatabaseError otherwise
-                # we could get an unexpected deadlock.
-                if nowait and not self.connection.features.has_select_for_update_nowait:
-                    raise DatabaseError('NOWAIT is not supported on this database backend.')
-                elif skip_locked and not self.connection.features.has_select_for_update_skip_locked:
-                    raise DatabaseError('SKIP LOCKED is not supported on this database backend.')
-                result.append(self.connection.ops.for_update_sql(nowait=nowait, skip_locked=skip_locked))
+            if for_update_part and not self.connection.features.for_update_after_from:
+                result.append(for_update_part)
 
             return ' '.join(result), tuple(params)
         finally: