CODEWITHSUNDEEP
djangodjango-modelsforeign-keysunique-constraint
Avocado
Avocado

Reputation: 911

Limit instantiations of class with particular value to one - django

I have two classes in a django app, project and plan

The project class has an is_global boolean field, as does the plan class. The plan also has a foreign key to the project class (projects have multiple plans).

I am trying to accomplish the following: for both projects and plans, there should only ever be one instance of each where is_global = true. The global plan should belong to the global project.

Is it possible to enforce this logic with django models?

Upvotes: 0

Views: 26

Answers (1)

SamSparx
SamSparx

Reputation: 5267

You could overwrite the save function of each model to check for prior 'is_global' items

Project Model

def save(self):
    if self.is_global:
        other_global = Project.objects.filter(is_global=True).exists()
        if other_global:
            #handle the error, eg, raise an exception or send a message
            return
    super.save()

Plan model

def save(self):
    if self.is_global:
        other_global = Plan.objects.filter(is_global=True).exists()
        if other_global:
            #handle the error, eg, raise an exception or send a message
            return
        if not self.project.is_global:
            #handle the error, eg, raise an exception or send a message
            return 
    super.save()

Upvotes: 1

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