Django ManyToMany model validation

Question

I have a model with a ManyToManyField similar to this one (the model Word has a language, too):

class Sentence(models.Model):
    words = models.ManyToManyFi         


        

Answer 1

It is not possible to do this validation in the model's clean method, but you can create a model form which can validate the choice of words.

from django import forms

class SentenceForm(forms.ModelForm):
    class Meta:
        model = Sentence
        fields = ['words', 'language']

    def clean(self):
        """
        Checks that all the words belong to the sentence's language.
        """
        words = self.cleaned_data.get('words')
        language = self.cleaned_data.get('language')
        if language and words:
            # only check the words if the language is valid
            for word in words:
                if words.language != language:
                    raise ValidationError("The word %s has a different language" % word)
        return self.cleaned_data

You can then customise your Sentence model admin class, to use your form in the Django admin.

class SentenceAdmin(admin.ModelAdmin):
    form = SentenceForm

admin.register(Sentence, SentenceAdmin)