Fix picking the value for a field when using grouped field choices

[sjhewitt]

If you have grouped the choices for a field, then the label of the first group is picked, rather than the first valid option. This change updates DynamicFixture to pick the first option from the flattened list of field options (i.e. field.flatchoices rather than field.choices)

[paulocheque]

Nice! I did not test it yet. Are you sure the field.flatchoices[0][0] indexes are ok?

[paulocheque]

Also, we need to check if there is some incompatibility issue with older versions of Django, like 1.2. Did you check that?

[sjhewitt]

flatchoices is a list created from field.choices, and guaranteed to be a list of 2-tuples, you can see how it is built here: https://github.com/django/django/blob/master/django/db/models/fields/__init__.py#L453

It was added in 2008, (https://github.com/django/django/commit/661f62be3c5f810fddd3b33bcbdfe33a3077a66d) which is pre-1.2, however I haven't run the test cases against 1.2. I'll try them now!

[sjhewitt]

Tests all pass against django==1.2.7

[paulocheque]

Nice! It is included in the travis script and it passes! I am just curious about the [0][0] indexes, but I will merge this pull request later. thanks!

[sjhewitt]

choices can be a list of tuples:

choices=(('a', 'A'), ('b', 'B'))

or a can contain a group header for sub-lists:

choices=(('Group Header', (('a', 'A'), ('b', 'B')), )

field.flatchoices flattens both the above choices into the same lists, so the [0][0] index is just used to pick the first valid choice in the list. When using grouped choices field.choices[0][0] would return 'Group Header' which is an invalid choice, but field.flatchoices[0][0] returns the first value from the first group ('a') which is a valid choice.

[paulocheque]

Nice! thanks a lot for your time!