Allen Bierbaum wrote:
> On Fri, May 16, 2008 at 4:54 PM, jason kirtland <[EMAIL PROTECTED]> wrote:
> [..]
>>> Anyway, I think this is a bit non-intuitive. What I propose instead
>>> is that SA could automatically set the 'keyword' attribute of the Note
>>> object as part of the process of assigning it to the mapped collection
>>> dictionary. This way the insert could look more like:
>>>
>>> item.notes['not-color'] = Note(value='blue')
>>>
>>> and behind the scenes SA would call: <new Note>.keyword = 'not-color'
>>>
>>> Any thoughts on this? Has anyone tried this in the past?
>> MappedCollection doesn't currently have a mismatch guard on __setitem__
>> (d[key] = val) or setdefault(), but easily could. There *is* a guard
>> protecting against item.notes = {'not-color': Note('color', 'blue')}, so
>> that machinery is available and applying it to the other setters is
>> straightforward.
>>
>> Automatically setting the value for the attribute_ and column_mapped
>> dict collections would be pretty convenient and DRY. This is a great
>> time to integrate that feature, if you want to try your hand at putting
>> together a patch and tests. If it's not too disruptive to existing
>> users it could slide right in as a new feature of 0.5.
>
> I would be more then happy to look into this (I already have), but I
> think my skills aren't quite up to the challenge. Could you point me
> in the general direction?
You might start looking at _convert here:
http://www.sqlalchemy.org/trac/browser/sqlalchemy/trunk/lib/sqlalchemy/orm/collections.py#L1402
It could be the case that that logic can be combined with the proposed
value-setting logic and used for @converter, __setitem__, etc.
The basic MappedCollection would probably have a default implementation
that does no attribute setting, being as there's no reasonable way to
intuit a reverse operation given only an arbitrary keying function
lambda. The attribute_ and column_mapped_ front ends would set up their
own implementations of the function that does key checking plus
attribute setting behavior.
> On a related note, I think it would be good to make this behavior come
> through a user customizable callback method that takes the index value
> and the newly assigned class item as values. This would allow users
> to add more automatic behavior that may be needed.
>
> For example I my current relationship is actually like this:
>
> 'input_vars' : relation(Var, primaryjoin = and_(script_table.c.id
> == var_table.c.script_id,
>
> var_table.c.input_output_type == 0),
>
> collection_class=column_mapped_collection(var_table.c.name)),
>
> So I would want to not only set the name automatically based on the
> key, but I would want to set the input_output_type to 0 in this case.
> Something like this would be good.
>
> def input_cb(key, item):
> item.name = key
> item.input_output_type = 0
If the setup I described above works out, this kind of thing could be
had pretty much for free.
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