Question

I have a question about this error and hope someone has ran into it like I have. I am getting this error on a model when trying to use the Models.ForeignKey field. I can verify that the table the foreign key is used in exists, as well as the table that the fk references exists. I can get the model to work if I use a CharField but that is no fun.

Here are the tables(using Postgresql 9.0) I did not design so please don’t rag on me too much if you do not like it, although I cannot guarantee I would have designed it any better:

Claim_status

     Column      |            Type             |                               Modifiers                                
-----------------+-----------------------------+------------------------------------------------------------------------
 claim_no        | character varying(30)       | not null
 claim_status    | character varying(15)       | 
 userid          | character varying(40)       | not null
 note            | character varying(255)      | 
 time            | timestamp without time zone | default now()
 claim_status_id | integer                     | not null default nextval('claim_status_claim_status_id_seq'::regclass)
Indexes:
    "claim_status_pkey" PRIMARY KEY, btree (claim_status_id)
    "ndx_claim_status_claim_no" btree (claim_no) CLUSTER
    "ndx_claim_status_claim_status" btree (claim_status)
    "ndx_claim_status_date_time" btree (date("time"))
    "ndx_claim_status_time" btree ("time")
    "ndx_claim_status_upper_userid" btree (upper(userid::text))
    "ndx_claim_status_userid" btree (userid)
Foreign-key constraints:
    "$1" FOREIGN KEY (claim_status) REFERENCES lk_claim_status(claim_status)
    "claim_status_claim_no_fkey" FOREIGN KEY (claim_no) REFERENCES claim(claim_no) ON UPDATE CASCADE

lk_claim_status

        Column        |         Type          |   Modifiers   
----------------------+-----------------------+---------------
 claim_status         | character varying(15) | not null
 description_internal | character varying(35) | not null
 description_web      | character varying(35) | not null
 display_insured_web  | boolean               | default false
 display_rep_web      | boolean               | default false
Indexes:
    "lk_claim_status_pkey" PRIMARY KEY, btree (claim_status)
Referenced by:
    TABLE "claim_status" CONSTRAINT "$1" FOREIGN KEY (claim_status) REFERENCES lk_claim_status(claim_status)

My models:

from django.db import models
from test.django.common.models.claim.lk_claim_status import LkClaimStatus

class ClaimStatus(models.Model):
    claim_no = models.CharField(max_length=40)
    # the foreign key does not work here, you get matching query error for some reason.
    claim_status = models.ForeignKey(LkClaimStatus, db_column='claim_status')
    #claim_status = models.CharField(max_length=15)
    userid = models.CharField(max_length=40)
    note = models.CharField(max_length=255)
    time = models.DateTimeField(auto_now=True)
    claim_status_id = models.AutoField(primary_key=True)
    class Meta:
        db_table = u'claim_status'

— end claim_status.py — start lk_claim_status.py

from django.db import models

class LkClaimStatus(models.Model):
    claim_status = models.CharField(max_length=15, primary_key=True)
    description_internal = models.CharField(max_length=35)
    description_web = models.CharField(max_length=35)
    display_insured_web = models.BooleanField()
    display_rep_web = models.BooleanField()
    class Meta:
        db_table = u'lk_claim_status'

I have not used in any pages yet but have just tested them out with the manage.py shell

Here have been my tests

from test.django.common.models.claim.claim_status import ClaimStatus
from test.django.common.models.claim.lk_claim_status import LkClaimStatus
status_list = ClaimStatus.objects.filter(claim_no='TEST')
for status in status_list:
  try:
    print status.claim_status.claim_status
  except LkClaimStatus.DoesNotExist:
    print "Got a blank one"

That last test prints out nothing but the except print statement. If I use the CharField option from the ClaimStatus model I can print a status.claim_status and get a value from the db table.

from test.django.common.models.claim.claim_status import ClaimStatus
from test.django.common.models.claim.lk_claim_status import LkClaimStatus
status_list = ClaimStatus.objects.filter(claim_no='TEST')
for status in status_list:
    print status.claim_status.claim_status

With the above test I get this:

>>> for status in status_list:
...     print status.claim_status.claim_status
... 
Traceback (most recent call last):
  File "<console>", line 2, in <module>
  File "/usr/lib/python2.5/site-packages/django/db/models/fields/related.py", line 315, in __get__
    rel_obj = QuerySet(self.field.rel.to).using(db).get(**params)
  File "/usr/lib/python2.5/site-packages/django/db/models/query.py", line 349, in get
    % self.model._meta.object_name)
DoesNotExist: LkClaimStatus matching query does not exist.

I would understand this if the table did not exist or the fields did not exist, but they do? I can verify as well that with the test there are no null values for that claim_status field in either table.

Answer 1

I can definitely see one problem with your models here. When you define a ForegnKey field with the name “claim_status”, Django will be automatically creating an attribute on your model instances called “claim_status_id” which will be used to store the raw value of the “claim_status” database column. However, you already have a primary key field with the same name, which probably leads to a conflict.

I am not sure what is the official way of solving this problem, but you could try to subclass ForeignKey and override its get_attname() method to return something else.