How can I set a ForeignKey on a specific attribute from another table?

Question

This is my first class Klant which means customer. It has an id, a customer-name and users from the customer which is a ManyToManyField referring to users from the the User-table django gives me.

class Klant(models.Model):
    id = models.AutoField(primary_key=True)
    klant_naam = models.CharField(max_length=100, default='-')
    klant_gebruiker = models.ManyToManyField(User)

    def __str__(self):
        return str(self.id) + " - " + self.klant_naam

This is the class Actie (Action or the action the user determines) which has an id, an action-name, an action-publish-date, an ending-date (the deadline), a customer-id which refers to Klant and actie_gebruiker that I want to refer to klant_gebruiker from the table Klant.

class Actie(models.Model):
    id = models.AutoField(primary_key=True)
    actie_naam = models.CharField(max_length=150, default='-')
    actie_aanmaakdatum = models.DateTimeField(default=datetime.now())
    actie_einddatum = models.DateTimeField(default=datetime.now() + timedelta(days=1))
    actie_klant = models.ForeignKey(Klant, default=1)
    actie_gebruiker = models.ForeignKey(Klant.klant_gebruiker, default=1)

    def __str__(self):
        return str(self.id) + " - " + self.actie_naam

So my question now is what do I have to do to set the value of actie_gebruiker to the attribute klant_gebruiker from the table Klant?

Answer 1

I believe you need to be using the through parameter for the ManyToManyField definition.

class Klant(models.Model):
    id = models.AutoField(primary_key=True)
    klant_naam = models.CharField(max_length=100, default='-')
    klant_gebruiker = models.ManyToManyField(User, through='Actie')

    def __str__(self):
        return str(self.id) + " - " + self.klant_naam


class Actie(models.Model):
    id = models.AutoField(primary_key=True)
    actie_naam = models.CharField(max_length=150, default='-')
    actie_aanmaakdatum = models.DateTimeField(default=datetime.now())
    actie_einddatum = models.DateTimeField(default=datetime.now() + timedelta(days=1))
    actie_klant = models.ForeignKey(Klant)
    actie_gebruiker = models.ForeignKey(User)

    def __str__(self):
        return str(self.id) + " - " + self.actie_naam

Answer 2

What you want is the to_field parameter on ForeignKeyField In your case it would be like actie_gebruiker = models.ForeignKey(Klant, to_field='klant_gebruiker' default=1)

But there's a problem, your klant_gebruiker is a ManyToManyField. What that means is in the database, there is another connecting table which keeps a foriegn key to to Klant and One to the target table which is User in your example. klant_gebruiker does not actually exist in your Table.

What you can do is create a through table and make your actie_gebruiker point to the foreign key field pointing to Klant Table, but there can be multiple records like that