How to filter items in the Foreign key field of the Django form?

Question

Good evening! I’m new to python/djagno, and I’m new to the community, too, that’s my first question.

What I want to do is filter the items from a selection list of a Foreign key (Template) on the plate registration screen.

Ex.: Show only what is True in the Active column of the table

register.py (models)

class Cadastro_placas(models.Model):
Numero_serie = models.CharField(
    'Número de série',
    max_length=120
)

Modelo = models.ForeignKey(
    'placas.modelo_placas', 
    related_name='modelo_placas_modelo',
    on_delete = models.PROTECT,
    null = True,
)

Revisao_lm = models.IntegerField(
    'Revisao LM'
)

Lote_numero = models.ForeignKey(
    'placas.cadastro_lote',
    related_name='numero_lote',
    on_delete = models.PROTECT
)

Observacao = models.TextField(
    'Observação',
    blank=True
)

def __str__(self):
    return self.Numero_serie

class Meta:
    db_table = 'CADASTRO_PLACAS'
    constraints = [
        models.UniqueConstraint(fields=['Numero_serie'], name="Constraint_placas")
    ]

model_boards (models)

class Modelo_placas(models.Model):
Modelo = models.CharField(
    'modelo',
    max_length=120
)

Descricao = models.CharField(
    'Descrição',
    max_length=200
)

Ativo = models.BooleanField(
    'Modelo Ativo',
    default=True
)



def __str__(self):
    return '{} - {}'.format(self.Modelo, self.Descricao) 

class Meta:
    db_table = 'MODELO_PLACAS'
    constraints = [
        models.UniqueConstraint(fields=['Modelo', 'Descricao'], name="Constraint_modelo")
    ]

cadastrar_placa (views)

def cadastrar_placa(request):
context = {
    "form": PlacaForm       
}
if request.method == "POST":
    form = PlacaForm(request.POST)
    if form.is_valid():
        form.save()      
return render(request, "placas/cadastrar-placa.html", context)

Forms.py (form)

class ModeloForm(forms.ModelForm):
class Meta:
    model = Modelo_placas
    fields = '__all__'

class PlacaForm(forms.ModelForm):
    class Meta:
        model = Cadastro_placas
        fields = '__all__'

register-board.html (html)

                    <form method="POST" class="post-form ">
                    {% csrf_token %}
                    <div class="form-row">
                        <div class="form-group col-md-8 mb-xl-1">
                            {{ form.Numero_serie  | as_crispy_field:"bootstrap"}}
                            {{ form.Revisao_lm | as_crispy_field:"bootstrap" }}
                        </div>
                    </div>
                    <div class="form-row">
                        <div class="form-group col-md-8 mb-xl-1">
                            {{ form.Lote_numero  | as_crispy_field:"bootstrap"}}
                        </div>
                        <div class="form-group col-md-1 mb-xl-0 ">
                            <a href="#"><img src="{% static 'placas/images/acrescer-png.png' %}" alt="+ lote"
                                    width=15 height=15 data-toggle="modal" data-target="#loteModal"></a>
                        </div>
                    </div>
                    <div class="form-row">
                        <div class="form-group col-md-8 mb-xl-4">
                            {{ form.Modelo | as_crispy_field:"bootstrap"}}
                        </div>
                    </div>
                    <div class="form-row">
                        <div class="form-group col-md-8 mb-xl-4">
                            {{ form.Observacao | as_crispy_field:"bootstrap"}}
                        </div>
                    </div>
                    <button type="submit" class="save btn btn-outline-primary col-md-8 mb-3  ">Salvar</button>
                </form>

Answer 1

I was able to solve my problem by placing the attribute limit_choices_to in the model field of the table Cadastro_placas, leaving the field as code below:

class Cadastro_placas(models.Model):   
Modelo = models.ForeignKey(
    'placas.modelo_placas', 
    related_name='modelo_placas_modelo',
    on_delete = models.PROTECT,
    null = True,
    limit_choices_to= {'Ativo': True} #Limita somente a modelos ativos
)

With this I got that appear only the models that are classified True in the Active field.

Answer 2

Vc can call the filter in Modelo_plates to get the list of active cards and then a for to fetch the respective entries

from .models import Modelo_placas, Cadastro_placas

def list_placas():
    modelos_ativos = Modelo_placas.filter(ativo=True) #retorna uma lista com as ocorrencias

    placas_ativas = []
    for modelo in modelos_ativos:
        placas_ativas.append(Cadastro_placas.objects.get(Modelo=modelo))
    data = {
        "placas":placas_ativas 
         }
    return render(request,'listaplacas', data)