[Sqlalchemy-tickets] [sqlalchemy] #2734: __eq__ operator appears to not be working correctly for decorated types

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

#2734: __eq__ operator appears to not be working correctly for decorated types
---------------------------+-----------------------------------------
 Reporter:  mcclurem       |           Owner:  zzzeek
     Type:  defect         |          Status:  new
 Priority:  medium         |       Milestone:
Component:  declarative    |        Severity:  no triage selected yet
 Keywords:  TypeDecorator  |  Progress State:  awaiting triage
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 So from the documentation it makes it appear that by defining
 `process_bind_param` and `process_result_value` I should have all the
 workings to transparently perform a translation. However the == operator
 doesn't perform the translation before sending the query to the db.
 Here's my example:
 {{{
 #!div style="font-size: 80%"
 {{{#!python
     class NullableString(TypeDecorator):
         '''Turns None into the string "Null" and back in order to prevent
 Null!=Null issues'''
         impl = String
         def process_bind_param(self, value, dialect):
             return "NONE" if value is None else value
         def process_result_value(self, value, dialect):
             return None if value == "NONE" else value
 }}}
 }}}
 If I have a class `SomeType` and I perform the following:
 {{{
 #!div style="font-size: 80%"
 {{{#!python
     session.query(SomeType).filter(SomeType.nullableStringCol ==
 None).all()
 }}}
 }}}
 I get no results but if I do:
 {{{
 #!div style="font-size: 80%"
 {{{#!python
     session.query(SomeType).filter(SomeType.nullableStringCol ==
 "NONE").all()
 }}}
 }}}
 I get my results.

 Now I can get around this by declaring the instance of the
 `NullableString` to use a custom comparator in `SomeType` but that seems
 like a broken paradigm because that comparison behavior should be captive
 within my new type.

 Am I misunderstanding the mechanism for the comparison?
 I apologize if this isn't a bug but it seems like it's broken (the example
 of typedecorators in the docs would presumably suffer the same problem
 when comparing unicode strings)

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Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2734>
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