Django 2 DB columns as FK to the same related table - Stack Overflow

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I have a table 'Athletes' and another table 'Parents'.

Table fields are: ATHLETES

  reg_number
  first_name
  last_name
  gender 
  age_group (as FK to AgeGroup)
  parent_1 (as FK to Parents using related_name='parent_1')
  parent_2 (as FK to Parents using related_name='parent_2')

PARENTS

  first_name
  last_name
  email
  phone

I have this working in the admin console where I can add parents to athletes.

I have a form that will display the related parents for each athlete.

Issue is trying to update the parent for a given athlete. POST has correct IDs for parent_1 and parent_2 but I get the following error within browser

ValueError at /save_athlete
Cannot assign "'1'": "Athletes.parent_1" must be a "Parents" instance.

POST has the following data showing in the payload

  id: 1
  reg_number: 12345
  group: 2
  first_name: amy
  last_name: small
  gender: Female
  parent_1: 1
  parent_2: 2

I don't understand the error so not sure what code would be useful to post here.

I had expected that the parent_1 and parent_2 values (ids) would be accepted when the form validates but it throws an error in views.py

I have a table 'Athletes' and another table 'Parents'.

Table fields are: ATHLETES

  reg_number
  first_name
  last_name
  gender 
  age_group (as FK to AgeGroup)
  parent_1 (as FK to Parents using related_name='parent_1')
  parent_2 (as FK to Parents using related_name='parent_2')

PARENTS

  first_name
  last_name
  email
  phone

I have this working in the admin console where I can add parents to athletes.

I have a form that will display the related parents for each athlete.

Issue is trying to update the parent for a given athlete. POST has correct IDs for parent_1 and parent_2 but I get the following error within browser

ValueError at /save_athlete
Cannot assign "'1'": "Athletes.parent_1" must be a "Parents" instance.

POST has the following data showing in the payload

  id: 1
  reg_number: 12345
  group: 2
  first_name: amy
  last_name: small
  gender: Female
  parent_1: 1
  parent_2: 2

I don't understand the error so not sure what code would be useful to post here.

I had expected that the parent_1 and parent_2 values (ids) would be accepted when the form validates but it throws an error in views.py

• django
• django-models
• django-views

Share Improve this question Follow edited Nov 21, 2024 at 4:07 Selcuk 59.4k1212 gold badges110110 silver badges115115 bronze badges asked Nov 21, 2024 at 3:30 SteveMSteveM 133 bronze badges

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2 Answers 2

Sorted by: Reset to default 0

Foreign keys accept ids, but only if they are of the correct type. If you look at the error message more closely:

Cannot assign "'1'": "Athletes.parent_1" must be a "Parents" instance.

You'll see that '1' is a string, not an integer. We don't see your code, but converting it to an int should solve the problem.

I have solved my problem. When I added the 2 Parent_ FKs to the model I did not update the forms.py to have additional code that Group FK was using.

def_clean_group code was existing.... I copied the example for parent_1 and the error moved to parent_2. created entry for parent_2 and problem resolved.

def clean_group(self):
    group = self.data['group'] if (self.data['group']).isnumeric() else 0
    try:
        group = models.Groups.objects.get(pk = group)
        return group
    except:
        raise forms.ValidationError("Invalid Selected.")

def clean_parent_1(self):
    parent_1 = self.data['parent_1'] if (self.data['parent_1']).isnumeric() else 0
    try:
        parent_1 = models.Parents.objects.get(pk = parent_1)
        return parent_1
    except:
        raise forms.ValidationError("Invalid Selected.")

def clean_parent_2(self):
    parent_2 = self.data['parent_2'] if (self.data['parent_2']).isnumeric() else 0
    try:
        parent_2 = models.Parents.objects.get(pk = parent_2)
        return parent_2
    except:
        raise forms.ValidationError("Invalid Selected.")

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