django - How to filter form based on foreign key?

Question

How can I filter fields in my TopForm in such a way that when a user selects a teacher, automatically all other fields show related values to the teacher. Suppose Adam is the teacher and in the Network department teaches network programming in the 4th semester(added in the admin). Now the user selects Adam, when Adam selected, the department dropdown shows only Network which is related to Adam and so on.

forms.py

class AnswerForm(ModelForm):
    class Meta:
        model = Student_Answer
        fields = ('answer',)
        labels = {'answer': ''}
        widgets = { 'answer': RadioSelect(choices=RATING_CHOICES)}


class TopForm(forms.Form):
    teacher = forms.ModelChoiceField(queryset=Teacher.objects.all())
    department = forms.ModelChoiceField(queryset=Department.objects.all())
    subject = forms.ModelChoiceField(queryset=Subject.objects.all())
    semester = forms.ModelChoiceField(queryset=Semester.objects.all())

models.py

class Question(models.Model):
    question = models.CharField(max_length=200)


class Department(models.Model):
    name = models.CharField(max_length=60)

class Semester(models.Model):
    num = models.IntegerField(choices=SEMESTER, default=1)

class Subject(models.Model):
    name = models.CharField(max_length=100)
    code = models.CharField(max_length=5, null=True)
    semester = models.ForeignKey(Semester, on_delete=models.CASCADE, null=True)
    department = models.ManyToManyField(Department)

class Teacher(models.Model):
    name = models.CharField(max_length=200)
    last_name = models.CharField(max_length=200, null=True)
    department = models.ManyToManyField(Department)
    subject = models.ForeignKey(Subject, on_delete=models.CASCADE)

class Student_Answer(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    teacher = models.ForeignKey(Teacher, on_delete=models.CASCADE)
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    subject = models.ForeignKey(Subject, on_delete=models.CASCADE)
    department = models.ForeignKey(Department, on_delete=models.CASCADE)
    semester = models.ForeignKey(Semester, on_delete=models.CASCADE)
    answer = models.SmallIntegerField(choices=RATING_CHOICES, default=None)

question from:https://stackoverflow.com/questions/65641033/how-to-filter-form-based-on-foreign-key

Answer 1

you can do this using js with an api. Example for api, graphene_django or django-rest-framework. And use VueJS on your template. When user selects a teacher you send get request to your api. Your api's response data becomes item for other select box. For example code:

in template.html

                  <div class="form-row">
                    <div class="col-md-12" style="padding-left:3px;">
                      <label for="id_faculty">Teachers</label>
                      <v-select :options="your_teachers" @input="selectTeacher($event)" label="name" v-model="selected_teacher"></v-select>
                    </div>
                  </div>
        <!-- Your deparments div begin --!>
                   <div class="form-row">
                    <div class="col-md-12" style="padding-left:3px;">
                      <label for="id_faculty">Deparments</label>
                      <v-select :options="departments" label="name" v-model="sselected_teacher_departments"></v-select>
                    </div>
                  </div>

when select a teacher your element run this function:

    getDepartment(){
      axios.get(url+'/api/?query={allDepartment{id, name}}').then((response) =>{
        this.department = response.data.data.allDepartment;
        this.loading = false;
      }).catch((error) => {
        console.log(error, 'for : getDepartment() function')
      });
    },