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Opened 8 years ago

Closed 7 years ago

#2608 closed defect (fixed)

multi-level foreignkey throws KeyError

Reported by: Gopal Narayanan <gopastro@…> Owned by: adrian
Component: contrib.admin Version:
Severity: minor Keywords:
Cc: Triage Stage: Ready for checkin
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: UI/UX:

Description

Example models:

class person(models.Model):
    pid = models.CharField(maxlength=20,
                           primary_key=True)
    name = models.CharField(maxlength=100)

class student(models.Model):
    student_pid = models.ForeignKey(person,
                                    db_column='student_pid',
                                    to_field='pid')

class student_option(models.Model):
    pid = models.ForeignKey(student,
                            to_field='student_pid')
    junk = models.IntegerField()

Note that student_option pid refers to student_pid which itself is a ForeignKey on student pointing to person.
Trying to generate SQL for these models throws KeyError: 'ForeignKey'

It appears that FKs are not allowed to point at a datatype that is itself a FK. It would be nice to allow multi-level foreign keys as there is a benefit in modeling legacy data with this kind of schema.

The patch attached simply enables the creation of SQL necessary for this to happen, by recursively diving down until we find the real underlying datatype.

Attachments (2)

multilevel_fk_patch.txt (628 bytes) - added by Gopal Narayanan <gopastro@…> 8 years ago.
multilevel_fk_patch.patch (710 bytes) - added by SmileyChris 7 years ago.
slightly simpler patch

Download all attachments as: .zip

Change History (4)

Changed 8 years ago by Gopal Narayanan <gopastro@…>

Changed 7 years ago by SmileyChris

slightly simpler patch

comment:1 Changed 7 years ago by SmileyChris

  • Triage Stage changed from Unreviewed to Ready for checkin

Although this is an obscure use-case, I validated that this does raise the above exception and that the patch fixes this.

comment:2 Changed 7 years ago by mtredinnick

  • Resolution set to fixed
  • Status changed from new to closed

(In [5106]) Fixed #2608 -- Generate correct SQL for multi-level foreign key relations.
Based on a patch from Gopal Narayanan.

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