Found explanation in :
http://web2py.com/books/default/chapter/29/06/the-database-abstraction-layer?search=._select%28%29
On Thursday, December 15, 2016 at 6:16:46 PM UTC+1, Anthony wrote:
>
> Looks like your current validator will not allow a category to be used
> twice in the entire item_category table, which is not consistent with a
> many-to-many relationship. Is that your intention? Or do you instead want
> to ensure that there are no duplicate item/category *combinations* in the
> item_category table. If the latter, you can do something like the
> following, which will not only provide the proper validation, but will also
> limit the list of categories in the select widget to those that have not
> already been paired with the current item:
>
> def show_grid():
> if 'item_category.item' in request.args:
> item_id = int(request.args[request.args.index('item_category.item'
> ) + 1])
> used_categories = db(db.item_category.item == item_id)._select(db.
> item_category.category)
> available_categories = db(~db.category.id.belongs(used_categories
> ))
> db.item_category.category.requires = IS_IN_DB(available_categories
> , 'category.id', '%(name)s')
> grid = SQLFORM.smartgrid(db.item)
> return dict(grid=grid)
>
> In smartgrid, when you are viewing item-categories for a given item,
> request.args will include "item_category.item", with the immediately
> following arg being the id of the item being viewed. So, in the above code,
> item_id is the id of the specific item in question. use_categories is a
> query that determines which categories have already been paired with this
> item in the item_categories table. It uses ._select so it can be passed
> to .belongs as a subquery. available_categories is a Set object that
> identifies categories that have *not* been paired with the current item
> in item_categories. When you pass a Set object to IS_IN_DB, it restricts
> values to records that are in the Set, so the validator will only allow
> (and display in the form) categories not already assigned to the item.
>
> Anthony
>
> On Wednesday, December 14, 2016 at 5:31:11 PM UTC-5, icodk wrote:
>>
>> I have an item ,category and item_category tables facilitating many to
>> many relations between items and categories, which enables an item to
>> belongs to several categories. I use SQLSmartgrid to show the
>> item_category table and to add categories to specific item. This all works
>> well. I can even managed to get an error if I select an already selected
>> category by using the following:
>>
>> db.item_category.category.requires = IS_IN_DB(db, 'category', '%(name)s',
>> _and=IS_NOT_IN_DB(db, 'item_category.category', error_message=T('This
>> category already assigned')), zero=None)
>>
>>
>> So what more could I wish ?
>>
>> It would be nice if the category dropdown list I get when adding or editing
>> category to an item would contains only the categories not yet assigned to
>> the item I am working on
>>
>> At the moment I get a list with all categories, however selecting an
>> existing category correctly give me an error as described above.
>>
>>
>>
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