sqlalchemy does not emit server_onupdate ON UPDATE clause with MySQL

Migrated issue, originally created by Charles-Axel Dein (@charlax)

This seems similar to #3155 and #2631.

I have this simple script to reproduce the problem:

from sqlalchemy import create_engine
from sqlalchemy import func
from sqlalchemy.dialects.mysql import DATETIME
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.schema import Column
from sqlalchemy.types import Integer, DateTime

Base = declarative_base()


class Timestamp(Base):

    __tablename__ = 'timestamps'

    id = Column(Integer(), primary_key=True)
    created_at = Column(DateTime(), nullable=False,
                        server_default=func.current_timestamp())
    updated_at = Column(DateTime(), nullable=False,
                        server_default=func.current_timestamp(),
                        server_onupdate=func.current_timestamp())


if __name__ == '__main__':
    engine = create_engine('mysql://root:root@localhost/test', echo=True)
    Base.metadata.drop_all(engine)
    Base.metadata.create_all(engine)

The SQL that sqlalchemy generates does not have the ON UPDATE clause:

CREATE TABLE timestamps (
	id INTEGER NOT NULL AUTO_INCREMENT,
	created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
	updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
	PRIMARY KEY (id)
)

A SHOW CREATE TABLE query confirms that fact:

CREATE TABLE `timestamps` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `created_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `updated_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |

I’m not 100% sure I’m not causing the problem or have fully understood the two similar tickets. I’ll read about it and follow up on this thread if I find something.

[sqlalchemy-bot]

Charles-Axel Dein (@charlax) wrote:

Leaving this for future reference, and people who might stumble upon this: http://jasonbos.co/two-timestamp-columns-in-mysql/

So basically getting a model with database-level created_at and updated_at behavior requires some shenanigans that you recommend against in #3155. Sadly, wasn’t able to find another way to achieve this.

from sqlalchemy import create_engine
from sqlalchemy import func, text
from sqlalchemy.dialects.mysql import TIMESTAMP
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.schema import Column
from sqlalchemy.types import Integer, DateTime
from sqlalchemy.orm import sessionmaker

Base = declarative_base()


class Timestamp(Base):

    __tablename__ = 'timestamps'

    id = Column(Integer(), primary_key=True)
    created_at = Column(TIMESTAMP(), nullable=False,
                        server_default=text('0'))
    updated_at = Column(TIMESTAMP(), nullable=False,
                        server_default=text('CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP'),
                        )


if __name__ == '__main__':
    engine = create_engine('mysql://root:root@localhost/test', echo=True)
    Base.metadata.drop_all(engine)
    Base.metadata.create_all(engine)

    Session = sessionmaker(bind=engine)
    session = Session()
    print session.execute('SHOW CREATE TABLE timestamps').fetchone()[1]

Which outputs:

2015-06-09 14:04:18,459 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'sql_mode'
2015-06-09 14:04:18,459 INFO sqlalchemy.engine.base.Engine ()
2015-06-09 14:04:18,460 INFO sqlalchemy.engine.base.Engine SELECT DATABASE()
2015-06-09 14:04:18,460 INFO sqlalchemy.engine.base.Engine ()
2015-06-09 14:04:18,461 INFO sqlalchemy.engine.base.Engine show collation where `Charset` = 'utf8' and `Collation` = 'utf8_bin'
2015-06-09 14:04:18,461 INFO sqlalchemy.engine.base.Engine ()
2015-06-09 14:04:18,462 INFO sqlalchemy.engine.base.Engine SELECT CAST('test plain returns' AS CHAR(60)) AS anon_1
2015-06-09 14:04:18,462 INFO sqlalchemy.engine.base.Engine ()
2015-06-09 14:04:18,462 INFO sqlalchemy.engine.base.Engine SELECT CAST('test unicode returns' AS CHAR(60)) AS anon_1
2015-06-09 14:04:18,463 INFO sqlalchemy.engine.base.Engine ()
2015-06-09 14:04:18,463 INFO sqlalchemy.engine.base.Engine SELECT CAST('test collated returns' AS CHAR CHARACTER SET utf8) COLLATE utf8_bin AS anon_1
2015-06-09 14:04:18,463 INFO sqlalchemy.engine.base.Engine ()
2015-06-09 14:04:18,464 INFO sqlalchemy.engine.base.Engine DESCRIBE `timestamps`
2015-06-09 14:04:18,464 INFO sqlalchemy.engine.base.Engine ()
2015-06-09 14:04:18,467 INFO sqlalchemy.engine.base.Engine
DROP TABLE timestamps
2015-06-09 14:04:18,467 INFO sqlalchemy.engine.base.Engine ()
2015-06-09 14:04:18,468 INFO sqlalchemy.engine.base.Engine COMMIT
2015-06-09 14:04:18,469 INFO sqlalchemy.engine.base.Engine DESCRIBE `timestamps`
2015-06-09 14:04:18,469 INFO sqlalchemy.engine.base.Engine ()
2015-06-09 14:04:18,470 INFO sqlalchemy.engine.base.Engine ROLLBACK
2015-06-09 14:04:18,470 INFO sqlalchemy.engine.base.Engine
CREATE TABLE timestamps (
	id INTEGER NOT NULL AUTO_INCREMENT,
	created_at TIMESTAMP NOT NULL DEFAULT 0,
	updated_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
	PRIMARY KEY (id)
)


2015-06-09 14:04:18,470 INFO sqlalchemy.engine.base.Engine ()
2015-06-09 14:04:18,479 INFO sqlalchemy.engine.base.Engine COMMIT
2015-06-09 14:04:18,479 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2015-06-09 14:04:18,480 INFO sqlalchemy.engine.base.Engine SHOW CREATE TABLE timestamps
2015-06-09 14:04:18,480 INFO sqlalchemy.engine.base.Engine ()
CREATE TABLE `timestamps` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `created_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
  `updated_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

And then, you need to pass a value of NULL on create:

mysql> insert into timestamps (id) value (1);
Query OK, 1 row affected (0.00 sec)

mysql> select * from timestamps;
+----+---------------------+---------------------+
| id | created_at          | updated_at          |
+----+---------------------+---------------------+
|  1 | 0000-00-00 00:00:00 | 2015-06-09 14:10:46 |
+----+---------------------+---------------------+
1 row in set (0.00 sec)

mysql> insert into timestamps (created_at, id) value (NULL, 2);
Query OK, 1 row affected (0.00 sec)

mysql> select * from timestamps;
+----+---------------------+---------------------+
| id | created_at          | updated_at          |
+----+---------------------+---------------------+
|  1 | 0000-00-00 00:00:00 | 2015-06-09 14:10:46 |
|  2 | 2015-06-09 14:11:14 | 2015-06-09 14:11:14 |
+----+---------------------+---------------------+
2 rows in set (0.00 sec)

[sqlalchemy-bot]

Charles-Axel Dein (@charlax) wrote:

Probably the last update here, left for posterity: was getting too complicated, so ended up defining all of this on the app side instead of database-side.