CODEWITHSUNDEEP
pythonmysqldjango
Carbon
Carbon

Reputation: 143

Django Primary key acting as a foreign key

I have a MySQL database with 9 tables. They are all related in some way, but I am having trouble with being able to connect with foreign keys. For example here are two of my tables that I am getting an error when I try to python manage.py migrate:

class Release(models.Model):
     release_ID = models.CharField(max_length=25, primary_key =True)
     releaseversion = models.CharField(max_length=25)
     model_ID = models.ForeignKey(Model, on_delete=models.CASCADE) #comes from Model class

class Subrelease(models.Model):
     subrelease_ID = models.CharField(max_length=25)
     release_ID = models.ForeignKey('Release', blank =True) #comes from Release class 
     subreleaseversion = models.CharField(max_length=25)

How would I make the primary key from class Release, which is release_ID also be the ForeignKey release_ID in class Subrelease? Any help would be much appreciated. Thank you.

After I run migrate I get this in cmd:

django.db.utils.InternalError: (1829, "Cannot drop column 'id': needed in a foreign 
    key constraint 'app_subrel_release_ID_id_8e08450_fk_app_release_id' of table
    'db.app_subrelease'")

UPDATE: Is this good/okay to do? I don't have any errors when migrating to DB ?

class Release(models.Model):
     #release_ID = models.CharField(max_length=25, primary_key =True)THIS WILL BE OUR PRIMARY KEY MADE BY DJANGO
     releaseversion = models.CharField(max_length=25)
     model = models.ForeignKey(Model, on_delete=models.CASCADE) #comes from Model class model_ID



class Subrelease(models.Model):
     #subrelease_ID = models.CharField(max_length=25) THIS WILL BE OUR PRIMARY KEY MADE BY DJANGO
     release = models.ForeignKey(Release, on_delete=models.CASCADE ) #comes from Release class release_ID
     subreleaseversion = models.CharField(max_length=25)

Upvotes: 1

Views: 3189

Answers (1)

mosesmeirelles
mosesmeirelles

Reputation: 427

You could try to use the to_field and db_column options.

class B(models.Model):
    name = models.ForeignKeyField(A, to_field="name", db_column="name")

Once you have created the foreign key, you can access the value and related instance as follows:

>>> b = B.objects.get(id=1)
>>> b.name_id # the value stored in the 'name' database column
>>> b.name # the related 'A' instance

reference: this answer

Upvotes: 2

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