De-selecting works the same as selecting multiple elements -- hold down
CTRL and then click the option. If you want something a little more
intuitive, you might look into the many available Javascript multi-select
widgets.
Anthony
On Saturday, January 30, 2016 at 12:29:50 PM UTC-5, Dave wrote:
>
> I was able to do some more testing and as I thought... everything works
> fine now that I got rid of the typo. And without requires= it does the
> right thing.
>
> One sorta related, but not really question... The <select multiple> box
> that gets created by default for that type of field... Is there any way to
> force it to put an option at the top for the equivalent of None? When
> editing a row in the database admin under appadmin, I can't seem to
> deselect all. In the real app, I will likely not allow the users to edit
> that, so I will be handling updates through model code... but just thought
> I would ask if there's an option in the Field definition I can add to force
> the first item in the select box to be empty/None. It appears there isn't
> a way for me to un-select in the browser once something is selected.
>
> Thanks again Anthony.
>
> On Friday, January 29, 2016 at 11:15:13 AM UTC-5, Anthony wrote:
>>
>> On Thursday, January 28, 2016 at 11:24:16 PM UTC-5, Dave wrote:
>>>
>>> Actually, maybe this is a bug. (or maybe just something that is not
>>> supposed to work the way I am trying to use it...)
>>>
>>> If I turn off lazy_table support, everything works. I get a
>>> multi-select box with the file_name populated (text area that I can
>>> multi-select).
>>>
>>
>> Actually, it is the reverse -- you get the multi-select box with
>> lazy_tables=True, but not with lazy_tables=False.
>>
>> Here is how it works. The multi-select widget is generated automatically
>> whenever a field has an IS_IN_DB(..., multiple=True) validator.
>> Furthermore, list:reference fields automatically get an IS_IN_DB validator,
>> but only when lazy_tables=True. The reason is that the IS_IN_DB validator
>> is created when the auto_validators() function is called, and that function
>> only assigns validators to reference fields if the referenced table name is
>> in db.tables. Here is the order of operations in each case:
>>
>> lazy_tables=True:
>>
>> 1. At the end of db.define_table(), the new "tablename" is added to
>> db.tables.
>> 2. Sometime later, when db.tablename is accessed, the table is fully
>> defined via db.lazy_define_table.
>> 3. db.lazy_define_table calls auto_validators, which adds the
>> IS_IN_DB validator because "tablename" is in db.tables (see #1).
>>
>> lazy_tables=False:
>>
>> 1. Before the end of db.define_table(), db.lazy_define_table is
>> called (prior to the new "tablename" being added to db.tables).
>> 2. db.lazy_define_table calls auto_validators, which does *not* add
>> the IS_IN_DB validator because "tablename" is *not *yet in db.tables
>> (see #1).
>> 3. The new "tablename" is added to db.tables *after*
>> db.lazy_define_table and auto_validators have already run.
>>
>> I'm not sure I would call it a bug, but I think we may be able to adjust
>> the code to make it work in either case (possibly by simply adding the new
>> tablename to db.tables *before* db.lazy_define_table is called within
>> db.define_table -- though I'm not sure if that will introduce some other
>> problem).
>>
>> Maybe open a Github issue and link to this thread.
>>
>> If you do not want to use lazy tables, there is a simple workaround --
>> just explicitly define the validator yourself:
>>
>> Field('children', 'list:reference file_entry',
>> requires=IS_IN_DB(db, 'file_entry.id', '%(file_name)s', multiple=
>> True))
>>
>> It appears you tried to do that, but you did not use the keyword argument
>> "requires" and instead passed the validator as the third positional
>> argument (which is actually the "length" argument).
>>
>> Note, the same issue exists with the default "represent" attribute of the
>> list:reference field -- you will need to use lazy tables or otherwise
>> explicitly specify that attribute as well.
>>
>> Anthony
>>
>>
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