Am Samstag, 5. Januar 2013 18:50:45 UTC+1 schrieb Michael Bayer:
>
>
> On Jan 5, 2013, at 7:42 AM, Alexander Jacob wrote:
>
> @compiles(i18NColumnClause)
> def compile_i18n_column_clause(element, compiler, **kw):
> return '%s_%s' % (element.name, GLOBAL_LANGUAGE)
>
> # custom type
> class i18NType(sqlalchemy.types.TypeDecorator):
> impl = sqlalchemy.types.Unicode
> def column_expression(self, colexpr):
> return i18NColumnClause(colexpr)
>
> # test class for custom type
> class Country(Base):
>
> __tablename__ = 'country'
> id = Column(Integer, primary_key=True)
> iso2 = Column(String(2))
> name = Column(i18NType(64))
>
> def __repr__(self):
> return "<Country(%d/%s/%s)>" % (self.id, self.iso2, self.name)
>
>
>
Thank you for the answer.
>
>> Interesting approach with the column_expression(), though that seems like
>> it would circumvent the labeling behavior of the compiler and cause more
>> complex expressions to fail. The INSERT case might work if you also
>> implemented bind_expression() but I'm not sure if that approach overall
>> doesn't break too much of the existing compilation functionality.
>>
>
You are right, it causes problems when doing complex queries like
joinedloads
session.query(IM).options(joinedload(IM.country)).get(4)
the generated sql gets broken like this:
%(57544816 country)s.name_en AS country_1_name
and then fails here
File "C:\Python27\lib\site-packages\sqlalchemy\engine\default.py", line
320, in do_execute
cursor.execute(statement, parameters)
File "C:\Python27\lib\site-packages\MySQLdb\cursors.py", line 159, in
execute
query = query % db.literal(args)
TypeError: format requires a mapping
>
> A more direct route with @compiles would be to compile Column, but still
> tricky, in particular that the compilation process for a Column is very
> involved. At the very least, for that to work it would have to be like
> this:
>
> class i18NColumn(Column): # note it has to be Column, not ColumnClause
> pass
>
> @compiles(i18NColumn)
> def compile(element, compiler, **kw):
> text = compile.visit_column(element, **kw)
> text = text.replace(element.name, '%s_%s' %(element.name,
> GLOBAL_LANGUAGE))
> return text
>
> so that existing labeling rules are not circumvented. but even that I'm
> not 100% sure might not have some gotchas.
>
I will try that
> Another variant on this would be to use the before_cursor_execute event to
> just do a search and replace on the SQL statement before it's passed to the
> DBAPI, I sometimes recommend that as well. Giving the "fake" column a name
> that clearly indicates internationalization, like Column("name_<i18N>"), is
> a good way to give a statement filter a clear path to where those names
> would go. If you need this translation behavior everywhere, that might be
> the best approach.
>
I preferred the event solution but
class Country(Base):
__tablename__ = 'country'
name = Column('name_<I18N>', String(64))
'SELECT country.`name_<I18N>` AS `country_name_<I18N>`, country.id AS
country_id, country.iso2 AS country_iso2
FROM country
WHERE country.id = %s'
gets properly replace in before_cursor_execute to
'SELECT country.`name_en` AS `country_name_en`, country.id AS country_id,
country.iso2 AS country_iso2
FROM country
WHERE country.id = %s'
and finally fails here:
Traceback (most recent call last):
File "C:\Program Files (x86)\JetBrains\PyCharm
2.5.2\helpers\pydev\pydevd.py", line 1401, in <module>
debugger.run(setup['file'], None, None)
File "C:\Program Files (x86)\JetBrains\PyCharm
2.5.2\helpers\pydev\pydevd.py", line 1055, in run
pydev_imports.execfile(file, globals, locals) #execute the script
File "C:/Projekte/interimexcellence/prototype/sqlalchemy/test.py", line
68, in <module>
print germany
File "C:/Projekte/interimexcellence/prototype/sqlalchemy/test.py", line
44, in __repr__
return "<Country(%d/%s/%s)>" % (self.id, self.iso2, self.name)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\attributes.py", line
251, in __get__
return self.impl.get(instance_state(instance), dict_)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\attributes.py", line
559, in get
"correctly" % key)
KeyError: "Deferred loader for attribute 'name' failed to populate
correctly"
The dict_ has no key 'name' :-(
Do you have any suggestions how to fix this?
> Though here, there's a less intrusive way to get this behavior if ORM
> level is all you need which is by using hybrids:
>
> class Country(Base):
> # ...
>
> name_de = Column(String)
> name_en = Column(String)
>
> @hybrid_property
> def name(self):
> return getattr(self, "name_%s" % GLOBAL_LANGUAGE)
>
> @name.setter
> def name(self, value):
> setattr(self, "name_%s" % GLOBAL_LANGUAGE, value)
>
> the above can be generalized:
>
> def make_hybrid(name):
> @hybrid_property
> def name_attr(self):
> return getattr(self, "%s_%s" % (name, GLOBAL_LANGUAGE))
>
> @name_attr.setter
> def name_attr(self, value):
> setattr(self, "%s_%s" % (name, GLOBAL_LANGUAGE), value)
>
> name_attr.__name__ = name
> return name_attr
>
>
This will work but this will load all columns from the db...
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