[Sqlalchemy-tickets] Issue #3339: AddConstraint example fails with binding error (zzzeek/sqlalchemy)

[Wichert A. <iss...@bi...>]

New issue 3339: AddConstraint example fails with binding error
https://bitbucket.org/zzzeek/sqlalchemy/issue/3339/addconstraint-example-fails-with-binding

Wichert Akkerman:

In order to support mark a constraint as deferrable with dialects that support it I use this code:

```python
def deferrable_supported(ddl, target, bind, **kw):
    """Check if deferrable constraints are supported.

    This function can be used as a callable for
    :ref:`execute_if <sqlalchemy:sqlalchemy.schema.DDLElement.execute_if>` to
    only run DDL statements on databases that support deferrable constraints.
    """
    return bind.dialect.name == 'postgresql'


def deferrable_not_supported(ddl, target, bind, **kw):
    """Check if deferrable constraints are not supported.

    This function can be used as a callable for
    :ref:`execute_if <sqlalchemy:sqlalchemy.schema.DDLElement.execute_if>` to
    only run DDL statements on databases that do not support deferrable
    constraints.
    """
    return bind.dialect.name not in ('postgresql', 'sqlite')


for constraint in _generic_sku_constraints:
    listen(SKU.__table__, 'after_create',
            schema.AddConstraint(constraint)
                .execute_if(callable_=deferrable_not_supported))

for constraint in _deferrable_sku_constraints:
    listen(SKU.__table__, 'after_create',
            schema.AddConstraint(constraint)
                .execute_if(callable_=deferrable_supported))
```

This code is modeled on the example in the [DDL chapter](http://docs.sqlalchemy.org/en/rel_0_9/core/ddl.html). This code fails with SQLAlchemy 0.9 with a `InvalidRequestError: This constraint is not bound to a table.  Did you mean to call table.append_constraint(constraint) ?` error.