> I forgot this was changed -- now AttributeError exceptions in the virtual
> fields function fail silently, simply foregoing the creation of the virtual
> field value for the record (which is why you got no error but didn't see
> the value in the record).
>
Gotcha, thanks!
>
>
>> Instead, it should be:
>>
>>
>>> db.myorder.c = Field.Virtual('c', lambda row: row.myorder.a * row.
>>> myorder.b)
>>>
>>> In the function, you must include the table name when accessing fields
>>> in the row. Also, note that even when creating the virtual field via
>>> assignment, you should still specify the name of the virtual field within
>>> Field.Virtual() -- otherwise the "name" attribute of the virtual field will
>>> be set to "unknown", which may cause problems in some contexts.
>>>
>>
>> Thanks for the enlightenment. I've tried your change, and now it gives me
>> the proper result. But i don't get your remark about the name attribute. I
>> can't find that in the book for new style virtual classes, can you offer me
>> a pointer? When looking at ">>> db.item.total_price =
>> Field.Virtual(lambda row: row.unit_price*row.quantity)" from the book
>> (mind the table name not being used here either) i thought the name
>> assignment would be automatic by using db.myorder.c
>>
>
> Note, the book code is actually:
>
> db.item.total_price = Field.Virtual(
> 'total_price',
> lambda row: row.item.unit_price*row.item.quantity)
>
>
>
Depends on where you look in the
book:
http://www.web2py.com/books/default/chapter/35/06/the-database-abstraction-layer
- i just copied that line yesterday. Because of the different i googled
'virtual fields web2py' and found both old and new documentation in the
book.
> Notice the first argument to Field.Virtual is 'total_price'. If you do
> that, then db.item.total_price.name will be 'total_price'. If you don't
> do that, then db.item.total_price.name will be 'unknown', which will
> cause problems in some cases where the field's "name" attribute is used.
> This is not explicitly mentioned in the book, though the book examples do
> include the name explicitly.
>
All clear when looking at the right page, thanks.
> Virtual fields are not stored in the database but are calculated after
>> records are pulled from the database, so they are not to be listed in the
>> call to .select().
>>
>
> Can a notimplemented exception be justified in such a case?
>>
>
> I think that particular exception is for methods within classes that have
> not been implemented. In any case, I don't think this case justifies a new
> custom exception. Should probably just be handled with documentation.
>
True, maybe a lookuperror might suite better, but then docs are a much
better solution anyway.
Remco
--
Resources:
- http://web2py.com
- http://web2py.com/book (Documentation)
- http://github.com/web2py/web2py (Source code)
- https://code.google.com/p/web2py/issues/list (Report Issues)
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