Incorrect primary key field used for right-hand table in join

[bruth]

Changing the following line https://github.com/cbmi/modeltree/blob/master/modeltree/tree.py#L174 to self.pk_column fixed the issue in the below models.

The offending code:

from django.db import models

class Specimen(models.Model):
    aliquot_id = models.DecimalField(decimal_places=0, max_digits=16, db_column='ALIQUOT_ID', primary_key=True) # Field name made lowercase.
    # snip...
    class Meta:
        db_table = u'specimen'
        verbose_name = 'specimen'
        verbose_name_plural = 'specimens'

class Subject(models.Model):
    study_id = models.TextField(primary_key=True, db_column='study_id')
    # snip...
    class Meta:
        db_table = u'subject'
        verbose_name = 'subject'
        verbose_name_plural = 'subjects'


class Link(models.Model):
    aliquot_id = models.ForeignKey(Specimen, db_column='ALIQUOT_ID', primary_key=True)
    study_id = models.ForeignKey(Subject, db_column='study_id')
    # snip...
    class Meta:
        db_table = u'link'

[bruth]

Holy sh*t. This has not been noticed simply because both tables in most joins that had been defined/tested have the same primary key field.. id.