CODEWITHSUNDEEP
pythondjangodatabasedjango-models
thinwybk
thinwybk

Reputation: 4743

How can I resolve or fix Django cyclic model field dependencies?

I've a database design corresponding to the following pseudo-code:

class AModel(models.Model):
    c_model_instances = models.OneToOne(CModel, ...)  # "is a" relationship

class BModel(models.Model):
    a_model_instances = models.ManyToMany(AModel, ...)  # "contains" relationship

class CModel(models.Model):
    b_model_instances = models.ManyToMany(BModel, ...)  # "contains" relationship

Belief it or not... this design makes total sense from a business perspective :) However of course I get an error NameError: name 'CModel' is not defined when I try to migrate the database. How can I resolve or fix (via different design) the issue?

Upvotes: 1

Views: 216

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 477854

You can use string literals, instead of an identifier that points to a model, as described in the documentation:

If you need to create a relationship on a model that has not yet been defined, you can use the name of the model, rather than the model object itself.

For example:

class AModel(models.Model):
    c_model_instances = models.OneToOne('django_app_name.CModel', …)  # "is a" relationship

class BModel(models.Model):
    a_model_instances = models.ManyToMany(AModel, …)  # "contains" relationship

class CModel(models.Model):
    b_model_instances = models.ManyToMany(BModel, …)  # "contains" relationship

Django will automatically replace the string literals with references to the models.

Upvotes: 1

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