CODEWITHSUNDEEP
djangoormdjango-modelsmany-to-many
Progger
Progger

Reputation: 2254

Django many to many relationship with join table-specific fields

I am migrating my app to Django and using their built-in ORM instead of writing SQL queries. The problem I am having is with one of my many to many relationships. I have the following models:

class Orgs(models.Model):
    org = models.AutoField(primary_key=True)
    org_name = models.CharField(max_length=45, null=False)
    org_hood = models.CharField(max_length=60, null=False)
    creation_date = models.DateField(auto_now_add=True)

class Members(models.Model):
    member_ID = models.AutoField(primary_key=True)
    user = models.OneToOneField(User)
    nick_name = models.CharField(max_length=20, null=False)
    is_self_managed = models.BooleanField(default=True)
    orgs = models.ManyToManyField(Orgs, null=True)

There are many Orgs and many Members. A member can be part of many Orgs and an Org can have many members. Each member has a balance ($0.00) associated to the Org they are a part of. For example:

member1 is in Org1 with a balance of $3.85
member1 is in Org2 with a balance of $2.00
member2 is in Org1 with a balance of $0.85

I can't figure out how to define this balance field. When I wasn't using the ORM, I manually created the join table and defined these fields I needed right in the join table.

Upvotes: 1

Views: 1778

Answers (1)

Kevin Christopher Henry
Kevin Christopher Henry

Reputation: 48952

Using the through argument to ManyToManyField you can explicitly define the join table and put the balance field there.

class Orgs(models.Model):
    ...
    members = ManyToManyField(Members, through='Membership')

class Members(models.Model):
    ...

class Membership(models.Model)
    org = models.ForeignKey(Orgs)
    member = models.ForeignKey(Members)
    balance = models.DecimalField()  # or whatever your field type is

Upvotes: 7

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