Web2Py DAL - How to check list:string type items for None

Question

I am trying to query a data set to return all list:string items not null. My example table:

db.define_table('newItems',
            Field('name', 'string'),
            Field('tasks', 'list:string'))

A query for None like so:

for item in db(db.newItems.tasks != None).select(db.newItems.tasks):

Returns:

[]
[]
[u'Wash Dog', u'Mow Yard']
[]
[u'Do X', u'Then do Y']
[]

How do I structure the query so that it only returns:

[u'Wash Dog', u'Mow Yard']
[u'Do X', u'Then do Y']

Thank you

update:

The answer works when tested on sqlite but it does not work with mongodb. The empty list [] is passed as '' that yields the wrong result:

In [4]: db.Tasks.email != []
Out[4]: <Query {'email': {'$ne': ''}}>

mongo shell:

> db.Tasks.find().count()
1195 (total records)

> db.Tasks.find({'email': {'$ne': ''}}).count()
1195

The correct query should be:

> db.Tasks.find({email: {$ne: [ ] }}).count()
108

Is this is a bug in mongo dal or is there another way I can specify the empty list?

Answer 1

If you input records via SQLFORM, empty values for task will get stored as an empty list rather than None, so you can do:

db(db.newItems.tasks != []).select(db.newItems.tasks)

Note, that will also exclude records that happen to have None values for task (which might exist if you have inserted records without task values using .insert() instead of a from).

UPDATE: Looks like the above doesn't work with MongoDB due to a bug in the MongoDB adapter.