根据另一个ModelMultipleChoice中先前选择的选项，在ModelMultipleChoice中显示不同的QuerySet

Question

I'm trying to build a simple Django webApp that stores documents in the server and it makes a relationship between the document and a project.

Here are my models:

class Project(models.Model):
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete='models.CASCADE', related_name='project_members')
    project_members = models.ManyToManyField(settings.AUTH_USER_MODEL)
    name = models.CharField(max_length=20, blank=False, null=False, unique=True)

    def __str__(self):
        return str(self.name)

class Document(models.Model):
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    path = models.FileField(upload_to='documents/')
    name = models.CharField(max_length=50)
    folders = models.ManyToManyField(Folder)
    projects = models.ManyToManyField(Project)


    def __str__(self):
        return str(self.name)

Here is the code of the form:

class RemoveFileProject(forms.Form):
    project_name = forms.ModelMultipleChoiceField(queryset=Project.objects.none())
    document_name = forms.ModelMultipleChoiceField(queryset=Document.objects.none(), widget=FilteredSelectMultiple("Documentos", is_stacked=False))

    def __init__(self, *args, **kwargs):
        user = kwargs.pop('user', None)
        super(RemoveFileProject, self).__init__(*args, **kwargs)
        if user:
            proyectos = Project.objects.filter(project_members=user)
            print(proyectos)
            self.fields['project_name'] = forms.ModelMultipleChoiceField(queryset=proyectos)
            docs = Document.objects.filter(projects=proyectos).select_related()
            self.fields['document_name'] = forms.ModelMultipleChoiceField(queryset=docs, widget=FilteredSelectMultiple("Documentos", is_stacked=False))

Now I have 2 problems:

1. I'm receiving a "ValueError: The QuerySet value for an exact lookup must be limited to one result using slicing". I understand that this is because proyectos is a QuerySet and they behave in unique ways but I'm having trouble to grasp how can I make a "join" in django.

2. I want to only show the documents that belong to each project, so If I choose the project "proyect 1", the second ModelMultipleChoiceFied should only display the documents that are related to "project 1".

Thanks in Advance

Answer 1

I would recommend looking into the Django Autocomplete Light (DAL) library, and specifically the forward attribute for widgets ( https://django-autocomplete-light.readthedocs.io/en/master/tutorial.html?highlight=forward#filtering-results-based-on-the-value-of-other-fields-in-the-form ). Works very well for what you're asking!