Re: [Sqlalchemy-tickets] [sqlalchemy] #2917: support "down" adaptions? (was: sqlalchemy.dialects.mysql.base.ENUM is not adaptable to sqlalchemy.sql.sqltypes.Enum) (was: sqlalchemy.dialects.mysql.base.ENUM is not adaptable to sqlalchemy.sql.sqltypes.Enum)

[sqlalchemy <mi...@zz...>]

#2917: support "down" adaptions?  (was: sqlalchemy.dialects.mysql.base.ENUM is not
adaptable to sqlalchemy.sql.sqltypes.Enum)
----------------------------------+------------------------------------
      Reporter:  jpcalderone      |      Owner:
          Type:  defect           |     Status:  new
      Priority:  medium           |  Milestone:
     Component:  mysql            |   Severity:  no triage selected yet
    Resolution:                   |   Keywords:
Progress State:  awaiting triage  |
----------------------------------+------------------------------------

Comment (by zzzeek):

 `strict` is not ignored, it is used by `mysql.ENUM.bind_processor`.   It's
 tested in mysql.test_types:EnumSetTest.test_enum which fails if you
 comment that line out, as currently the ENUM is adapted to a new object
 with the same type.

 The issue here is related to what I would characterize as unintended use
 of the `adapt()` method - this method is until now only intended for "up"
 adaptions, that is from a more generic type to a dialect-specific type,
 and not for a "down" adaption from a specific type to a more general.
 That use case doesn't exist within SQLAlchemy internals.

 What's special about "strict" here as opposed to all the other custom
 keyword arguments that other MySQL types and other types from other
 dialects include, is that it is dialect-specific but also affects the
 runtime type-coercion behavior.  That's why this special adapt() method
 exists - because adapt() is already only used to produce a new type object
 that's appropriate for run-time type coercion.

 in the vast majority of cases elsewhere I've just looked at, types have
 predictable argument signatures because all keyword arguments are
 ultimately explicitly within the `__init__` method of the type itself or a
 superclass; the default adapt() method looks at `__bases__` to get at
 these additional arguments.   `Enum` is special because it starts out with
 `*varargs`, and Python 2 doesn't provide Py3K's nice "keyword-only
 arguments" feature that we'd otherwise be using here.

 We have a suite that tests all possible legal "up" adaptions but not
 "down" adaptions.  That would need to be added.  Autocode should be able
 to fix this right now just by using the adapt() of the general type:

 {{{
    Enum.adapt(meta.tables['foo'].columns['bar'].type, Enum)
 }}}

--
Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2917#comment:1>
sqlalchemy <http://www.sqlalchemy.org/>
The Database Toolkit for Python