Question

I have a Person model and I am using a django form to edit another object with a foreign key to Person. The person model has first_name and last_name fields. I want to run a method to filter results for the drop down box of the foreign reference.

I am trying to use values_list() to override the form field options (choices property) like so:

data.form.fields['person'].choices = GetPersons().values_list('id', 'first_name')

GetPersons() just filters the Person class like

return Person.objects.filter(id__gt=1000)`

for example, so I only get people I want to show up. How can I use values_list() to return the concatenation of first_name and last_name without having to return a dictionary and splitting everything manually?

Answer 1

I have in mind 2 sugestions for you:

• First one is to concatenate fields in database with extra . For me is a dirty solutions but can run.

Sample:

persons =  GetPersons().extra(select={'full_name': "concatenate( first, last) "} )
choices = persons.values_list('id', 'full_name')

and …

• the second one use list comprehension:

Sample:

choices = [ ( p.id, '{0} {1}'.format( p.first, p.last ),) for p in GetPersons() ]

Edited 2018

Concat is now available as database function:

>>> from django.db.models import CharField, Value as V
>>> from django.db.models.functions import Concat
>>> persons = GetPersons().annotate(
...     full_name=Concat(
...         'last', V(', '), 'first', V('.'),
...         output_field=CharField()
...     )
... )