External DB layout, two column as PK, modification not possible

[Kevin Olbrich]

Hi!

I got the following table definition on inspect db:

class KevinExample(models.Model):
    code = models.CharField(db_column='Code', primary_key=True, max_length=50)  # Field name made lowercase.
    lineid = models.IntegerField(db_column='LineId')  # Field name made lowercase.
    object = models.CharField(db_column='Object', max_length=20, blank=True, null=True)  # Field name made lowercase.
    loginst = models.IntegerField(db_column='LogInst', blank=True, null=True)  # Field name made lowercase.
    u_contrattr = models.ForeignKey('KevinExpAttr', models.DO_NOTHING, db_column='U_contrattr', max_length=50, blank=True, null=True)  # Field name made lowercase.
    u_attrlinedata = models.CharField(db_column='U_attrlinedata', max_length=50)  # Field name made lowercase.
    class Meta:
        managed = False
        db_table = '@KEVIN_EXAMPLE'
        unique_together = (('code', 'lineid'),)

Inserting new rows by using the constructor and force_insert works fine but refresh_from_db() as well as save() is not possible (duplicate key constraint).

Problem is, code + lineid is PK and I have to keep it like this (foreign table).

Is there a workaround for this? Is it still impossible to define such PK on latest Django?

Kind regards

Kevin

[Matthew Pava]

I did some Google searches for you.

There’s still an open ticket for it, open for the past 12 years:

https://code.djangoproject.com/ticket/373

 

There’s plenty of people asking the same question.  Here’s one on Stack Overflow:

https://stackoverflow.com/questions/16800375/how-can-set-two-field-primary-key-for-my-models-in-django

 

And it looks like there’s an app for it that hasn’t been updated since 2014:

https://github.com/simone/django-compositekey

 

In short, though, it looks like you’re doing everything correctly.  You could always overwrite the save method and the refresh_from_db method for your use case.

 

If you can change the table at all, I would add an ID column and skip specifying the primary_key column in the model.  You could also make a new view inside the database that is an interface to the foreign table and write your trigger SQL in your database system to handle inserts, updates, and deletes.

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