pythondjangomany-to-many

How to add column in ManyToMany Table (Django)


From the example of Django Book, I understand if I create models as following:

from xxx import B

class A(models.Model):
    b = ManyToManyField(B)

The Django would create a new table(A_B) beyond Table A, which has three columns:

But now I want to add a new column in the Table A_B, thus would be very easy if I use normal SQL, but now anyone can help me how to do? I can't find any useful information in this book.


Solution

  • It's very easy using django too! You can use through to define your own manytomany intermediary tables

    Documentation provides an example addressing your issue:

    Extra fields on many-to-many relationships
    
    class Person(models.Model):
        name = models.CharField(max_length=128)
    
        def __unicode__(self):
            return self.name
    
    class Group(models.Model):
        name = models.CharField(max_length=128)
        members = models.ManyToManyField(Person, through='Membership')
    
        def __unicode__(self):
            return self.name
    
    class Membership(models.Model):
        person = models.ForeignKey(Person, on_delete=models.CASCADE)
        group = models.ForeignKey(Group, on_delete=models.CASCADE)
        date_joined = models.DateField()
        invite_reason = models.CharField(max_length=64)