[Sqlalchemy-tickets] Issue #3635: Explicitly set column value overriden by older initialization val

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New issue 3635: Explicitly set column value overriden by older initialization value of relationship property
https://bitbucket.org/zzzeek/sqlalchemy/issues/3635/explicitly-set-column-value-overriden-by

Torsten Landschoff:

I lately updated my application from SQLAlchemy 0.7.10 to 1.0.11 and expected no problems (the reason for the late update was PyInstaller, which did not manage to build an executable with a new SQLAlchemy).

However, after a while of testing I ran into the following behaviour in SA 1.0.1:

1. I create a mapped instance and the ``__init__`` initializes a few relationship properties to `None`, making my IDE happy that everything is set up in `__init__`.
2. The foreign key column underlying the relationship is explicitly set to a specific value.
3. During commit I run into ``IntegrityError``, because the column value is reset to NULL.

The attached example `relation_overrides_column.py` illustrates the problem. With SA 0.7.8 I got the expected output:

```
$ pip install sqlalchemy==0.7.10
Collecting sqlalchemy==0.7.10
Installing collected packages: sqlalchemy
Successfully installed sqlalchemy-0.7.10
$ python relation_overrides_column.py 
[Schema creation commands]
2016-01-21 23:07:40,690 INFO sqlalchemy.engine.base.Engine COMMIT
2016-01-21 23:07:40,692 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2016-01-21 23:07:40,692 INFO sqlalchemy.engine.base.Engine INSERT INTO customer (name) VALUES (?)
2016-01-21 23:07:40,693 INFO sqlalchemy.engine.base.Engine ('William',)
2016-01-21 23:07:40,693 INFO sqlalchemy.engine.base.Engine COMMIT
2016-01-21 23:07:40,693 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2016-01-21 23:07:40,694 INFO sqlalchemy.engine.base.Engine INSERT INTO "order" (customer_name) VALUES (?)
2016-01-21 23:07:40,694 INFO sqlalchemy.engine.base.Engine ('William',)
2016-01-21 23:07:40,694 INFO sqlalchemy.engine.base.Engine COMMIT
```

compared to SA 1.0.11:

```
$ pip install sqlalchemy==1.0.11
Collecting sqlalchemy==1.0.11
Installing collected packages: sqlalchemy
  Found existing installation: SQLAlchemy 0.7.10
    Uninstalling SQLAlchemy-0.7.10:
      Successfully uninstalled SQLAlchemy-0.7.10
Successfully installed sqlalchemy-1.0.11
$ python relation_overrides_column.py 
[Test casting and DDL setup]
2016-01-21 23:09:16,537 INFO sqlalchemy.engine.base.Engine COMMIT
2016-01-21 23:09:16,541 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2016-01-21 23:09:16,542 INFO sqlalchemy.engine.base.Engine INSERT INTO customer (name) VALUES (?)
2016-01-21 23:09:16,542 INFO sqlalchemy.engine.base.Engine ('William',)
2016-01-21 23:09:16,543 INFO sqlalchemy.engine.base.Engine COMMIT
2016-01-21 23:09:16,543 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2016-01-21 23:09:16,544 INFO sqlalchemy.engine.base.Engine INSERT INTO "order" (customer_name) VALUES (?)
2016-01-21 23:09:16,544 INFO sqlalchemy.engine.base.Engine (None,)
2016-01-21 23:09:16,545 INFO sqlalchemy.engine.base.Engine ROLLBACK
Traceback (most recent call last):
  File "relation_overrides_column.py", line 37, in <module>
    session.commit()
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 813, in commit
    self.transaction.commit()
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 392, in commit
    self._prepare_impl()
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 372, in _prepare_impl
    self.session.flush()
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 2027, in flush
    self._flush(objects)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 2145, in _flush
    transaction.rollback(_capture_exception=True)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 60, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 2109, in _flush
    flush_context.execute()
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/orm/unitofwork.py", line 373, in execute
    rec.execute(self)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/orm/unitofwork.py", line 532, in execute
    uow
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/orm/persistence.py", line 174, in save_obj
    mapper, table, insert)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/orm/persistence.py", line 800, in _emit_insert_statements
    execute(statement, params)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 914, in execute
    return meth(self, multiparams, params)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/sql/elements.py", line 323, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1010, in _execute_clauseelement
    compiled_sql, distilled_params
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1146, in _execute_context
    context)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1341, in _handle_dbapi_exception
    exc_info
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/util/compat.py", line 200, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1139, in _execute_context
    context)
  File "/opt/dynasdk/loco2-precise/lib/python2.7/site-packages/sqlalchemy/engine/default.py", line 450, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.IntegrityError: (pysqlite2.dbapi2.IntegrityError) NOT NULL constraint failed: order.customer_name [SQL: u'INSERT INTO "order" (customer_name) VALUES (?)'] [parameters: (None,)]
```

In this example it is easy to fix by not setting the relation `self.customer = None` in `__init__``, but I basically have to change all my classes to make sure that they never set a relationship if column access might happen later to write the actual value.

Any thoughts on this? Was this by accident or a deliberate change in behaviour?

[Sqlalchemy-tickets] Issue #3635: Explicitly set column value overriden by older initialization val

[Sqlalchemy-tickets] Issue #3635: Explicitly set column value overriden by older initialization value of relationship property (zzzeek/sqlalchemy)