Re: Set of choices of which several can be chosen without using a ManyToManyField

On 11/01/2011 09:05 AM, Jaroslav Dobrek wrote:
>> You are confusing model fields with form fields. MultipleChoiceField
>> is a form field, not a model field.
> I wasn't aware of the existence of MultipleChoiceFields. The idea of
> the above code was to express that I wanted to use this code
>
> class Candidate(models.Model):
>
> programming_languages = models.CharField(max_length=50, choices=(
>
> (u'Python)', u'Python'),
> (u'C++', u'C++'),
> (u'Java', u'Java'),
> # ...
> ), blank=True)
>
> with the only exception that, in the admin interface, several choices
> are possible when one creates a new candidate object. I.e. I want
> admins to be able to create a candidate that knows, say Python *and* C+
> + by choosing both of these languages during the creation of the
> object. I used the string "MultipleChoiceField" as a dummy for
> whatever should be used instead.
>
> Jaroslav
>
>
>
>
>
>
>> If you want a field that will be represented by a MultipleChoiceField
>> in model, you simply need to define 'choices' on a field class.
>>
>> https://docs.djangoproject.com/en/1.3/ref/models/fields/#choices
>>
>> Cheers
>>
>> Tom
Still, you want to control the input at the form level, not the model
level. Create a ModelForm for your Candidate, but override the language
field to take a MultipleChoiceField, and then override the __init__()
and save() methods to handle them properly. "Properly," of course, is
determined by your application, and how you want to store the
information in the database. You could choose to store it in a
CharField as a comma separated list of language names, or in an
IntegerField as a bit field (0x1 = 'Python', 0x2 = 'Perl', 0x4 = PHP, so
0x5 means the user knows Python and PHP, but not Perl). The latter is a
more efficient way to store the data, but the former is arguably more
human-friendly.

Ultimately, though, it seems that you are adding complexity rather than
removing it. This is exactly what many to many relationships are
designed to handle. If you want to use another method, you have to
figure out the details for yourself.

Cheers,
Cliff

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