ModelChoiceField\label_from_instance or how to make Choices using data from 2 models to display countries in user profile?

Question

Django

Good day
I want to give the user the opportunity to choose their country. One model has country data, the other has country translations. I did it through ModelChoiceField with redefining label_from_instance , but the problem is that because of this label_from_instance itself, the number of requests grows and the page takes a long time to load. Tell me how to speed up / implement the solution in a different way?

# admindivisions.models
class Countries(models.Model):
    osm_id = models.IntegerField(db_index=True, null=True)
    status = models.IntegerField()
    population = models.IntegerField(null=True)
    iso3166_1 = models.CharField(max_length=2, blank=True)
    iso3166_1_a2 = models.CharField(max_length=2, blank=True)
    iso3166_1_a3 = models.CharField(max_length=3, blank=True)
    class Meta:
        db_table = 'admindivisions_countries'
        verbose_name = 'Country'
        verbose_name_plural = 'Countries'

class CountriesTranslations(models.Model):
    common_name = models.CharField(max_length=81, blank=True, db_index=True)
    formal_name = models.CharField(max_length=100, blank=True)
    country = models.ForeignKey(Countries, on_delete=models.CASCADE, verbose_name='Details of Country')
    lang_group = models.ForeignKey(LanguagesGroups, on_delete=models.CASCADE, verbose_name='Language of Country',
                                   null=True)
    class Meta:
        db_table = 'admindivisions_countries_translations'
        verbose_name = 'Country Translation'
        verbose_name_plural = 'Countries Translations'

 # profiles.forms
class CountriesChoiceField(forms.ModelChoiceField):
    def __init__(self, user_lang='en', *args, **kwargs):
        super(CountriesChoiceField, self).__init__(*args, **kwargs)
        self.user_lang = user_lang
    def label_from_instance(self, obj):
        return obj.countriestranslations_set.get(lang_group=self.user_lang)

class UserProfileForm(forms.ModelForm):
user_lang = user_lang_here
country = CountriesChoiceField(
    queryset=Countries.objects.filter(
        status=1, iso3166_1__isnull=False,
        countriestranslations__lang_group=user_lang).order_by('countriestranslations__common_name'),
    widget=forms.Select(), user_lang=user_lang)
    class Meta:
        model = UserProfile()
        fields = ('email', 'email_privacy',
                  'profile_url',
                  'first_name', 'last_name',
                  'country',)

Tried using ChoiceField via tuple generation

# profiles.forms
class UserProfileForm(forms.ModelForm):
    # PREPARE CHOICES
    country_choices = ()
    lang_group = Languages.objects.get(iso_code='en').group
    for country in Countries.objects.filter(status=1):
        eng_name = country.countriestranslations_set.filter(lang_group=lang_group).first()
        if eng_name:
            country_choices += ((country, eng_name.common_name),)
    country_choices = sorted(country_choices, key=lambda tup: tup[1])
    country = forms.ChoiceField(choices=country_choices, required=False)
    class Meta:
        model = UserProfile()
        fields = ('email', 'email_privacy',
                  'profile_url',
                  'first_name', 'last_name',
                  'country',)
# profiles.views
def profile_settings(request):
    if request.method == 'POST':
        user_profile_form = UserProfileForm(request.POST, instance=request.user)
        if user_profile_form.is_valid():
            user_profile_form.save()
            messages.success(request, _('Your profile was successfully updated!'))
            return redirect('settings')
        else:
            messages.error(request, _('Please correct the error below.'))
    else:
        user_profile_form = UserProfileForm(instance=request.user)
    return render(request, 'profiles/profiles_settings.html', {
        'user_profile_form': user_profile_form,
    })

But Exception Value occurs: Cannot assign “'AF'”: “UserProfile.country” must be a “Countries” instance. on the line if user_profile_form.is_valid():
Thank you.

Answer 1

Solution

class CountriesChoiceField(forms.ModelChoiceField):
    def __init__(self, user_lang, *args, **kwargs):
        queryset = Countries.objects.filter(
            status=1, iso3166_1__isnull=False,
            countriestranslations__lang_group=user_lang).order_by('countriestranslations__common_name')

        super(CountriesChoiceField, self).__init__(queryset, *args, **kwargs)

        self.translations = OrderedDict()
        for country in queryset:
            name = country.countriestranslations_set.get(lang_group=user_lang).common_name
            self.translations[country] = name

    def label_from_instance(self, obj):
        return self.translations[obj]

class UserProfileForm(forms.ModelForm):
    user_lang = user_lang_here
    country = CountriesChoiceField(widget=forms.Select(), user_lang=user_lang)

    class Meta:
        model = UserProfile()
        fields = ('email', 'email_privacy',
                  'profile_url',
                  'first_name', 'last_name',
                  'country',)

As a result, we have 7 queries in 29.45ms versus 73 queries in 92.52ms