diff options
Diffstat (limited to 'lib/sqlalchemy/dialects/mssql/base.py')
| -rw-r--r-- | lib/sqlalchemy/dialects/mssql/base.py | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/lib/sqlalchemy/dialects/mssql/base.py b/lib/sqlalchemy/dialects/mssql/base.py index fe1e94a53..31c55917b 100644 --- a/lib/sqlalchemy/dialects/mssql/base.py +++ b/lib/sqlalchemy/dialects/mssql/base.py @@ -418,6 +418,40 @@ Declarative form:: This option can also be specified engine-wide using the ``implicit_returning=False`` argument on :func:`.create_engine`. +.. _mssql_rowcount_versioning: + +Rowcount Support / ORM Versioning +--------------------------------- + +The SQL Server drivers have very limited ability to return the number +of rows updated from an UPDATE or DELETE statement. In particular, the +pymssql driver has no support, whereas the pyodbc driver can only return +this value under certain conditions. + +In particular, updated rowcount is not available when OUTPUT INSERTED +is used. This impacts the SQLAlchemy ORM's versioning feature when +server-side versioning schemes are used. When +using pyodbc, the "implicit_returning" flag needs to be set to false +for any ORM mapped class that uses a version_id column in conjunction with +a server-side version generator:: + + class MyTable(Base): + __tablename__ = 'mytable' + id = Column(Integer, primary_key=True) + stuff = Column(String(10)) + timestamp = Column(TIMESTAMP(), default=text('DEFAULT')) + __mapper_args__ = { + 'version_id_col': timestamp, + 'version_id_generator': False, + } + __table_args__ = { + 'implicit_returning': False + } + +Without the implicit_returning flag above, the UPDATE statement will +use ``OUTPUT inserted.timestamp`` and the rowcount will be returned as +-1, causing the versioning logic to fail. + Enabling Snapshot Isolation --------------------------- |