#26827: "ModelState.fields cannot refer to a model class ... Use a string
reference
instead." when using custom model field derived from ManyToMany
----------------------------+--------------------
Reporter: rrauenza | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 1.9
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
----------------------------+--------------------
I ended up in a weird situation (Django 1.9.7) where I couldn't make any
additional migrations. So I reset my migrations thinking the problem was
somehow in the migration scripts themselves:
{{{
ValueError: ModelState.fields cannot refer to a model class -
"runs.to" does. Use a string reference instead.
}}}
I still got the error after restarting migrations from scratch, so I
determined it is about the migration looking at the currently declared
models, not the historical model migration scripts.
I have this (trimmed) code:
{{{
class _RunsField(models.ManyToManyField):
def __init__(self, *args, **kwargs):
super(_RunsField, self).__init__(Run,
through='BaselineAssignment')
class Baseline(models.Model):
runs = _RunsField()
class BaselineAssignment(models.Model):
run = models.ForeignKey('Run', on_delete=models.CASCADE)
baseline = models.ForeignKey('Baseline', on_delete=models.CASCADE)
}}}
If I change {{{Run}}} in the {{{__init__}}} in {{{_RunsField}}} to
{{{'Run'}}} (quoted) the problem goes away.
This seems like this is something that should have been handled by the
underlying migration code, and even if it isn't, the error message is
quite unhelpful.
--
Ticket URL: <https://code.djangoproject.com/ticket/26827>
Django <https://code.djangoproject.com/>
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