Distinct Values in ModelChoiceField

[Joseph Mutumi]

Hello,

I have a model that has a foreign key field that I want to use in a form as a select box.
That particular field at times appears multiple times in the database. How do I make it
only have distinct values?

This is a snippet, drop down will have repeated values if same color is entered:

class FavoriteColor(models.Model):
    color = models.CharField(max_length=255)

    def __unicode__(self):
        return self.color

class FavoriteThings(models.Model):
    name = models.CharField(max_length=10)
    color = models.ForeignKey(FavoriteColor)

class FavoriteThingsForm(forms.ModelForm):
    class Meta:
        model = FavoriteThings

Thank you

[Sithembewena Lloyd Dube]

I reckon you could try the following:
- declare a function which does a 'select distinct' and returns the queryset via the ORM
e.g.

def distinct_colors():
    results = FavoriteColor.objects.all().values("color").distinct()
    return results

then ...

class FavoriteThingsForm(forms.ModelForm):
    color = forms.ModelChoiceField(queryset=distinct_colors)

I think that you may have to explicitly declare all your form fields and get rid of the class Meta declaration. Not verified, so head here for more information: https://docs.djangoproject.com/en/dev/ref/forms/fields/#modelchoicefield

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Regards,
Sithembewena Lloyd Dube

[Melvyn Sopacua]

On 20-8-2012 0:16, Joseph Mutumi wrote:

> That particular field at times appears multiple times in the database. How
> do I make it
> only have distinct values?
>
> This is a snippet, drop down will have repeated values if same color is
> entered:
>
> class FavoriteColor(models.Model):
> color = models.CharField(max_length=255)
>
> def __unicode__(self):
> return self.color

You should invest in fixing the flaw in the design. Set the unique
attribute on the color field after you manually remove all duplicates
from the database.


--
Melvyn Sopacua

[Sithembewena Lloyd Dube]

Hi Melvyn,

I found your response to the OP interesting, yet I cannot quite follow it. Even if he sets a unique attribute (presumably Boolean/ Checkbox?), he would still need a mechanism to filter the result set at runtime? Please expound?

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[Melvyn Sopacua]

On 22-8-2012 3:04, Sithembewena Lloyd Dube wrote:

> I found your response to the OP interesting, yet I cannot quite follow it.
> Even if he sets a unique attribute (presumably Boolean/ Checkbox?)

Nope, this unique attribute:
<https://docs.djangoproject.com/en/1.4//ref/models/fields/#unique>

By design, the foreign key will now not contain duplicates so distinct
is no longer necessary.
--
Melvyn Sopacua

[Sithembewena Lloyd Dube]

@Melvyn, thanks - that makes sense.

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Melvyn Sopacua

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[Joseph Mutumi]

@Melvyn Thank you. It actually worked out as you said. It needed a redesign.