#28301: Object history is not logged for many to many fields
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Reporter: Karolis Ryselis | Owner: nobody
Type: Bug | Status: new
Component: contrib.admin | Version: 1.11
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Consider this models.py:
{{{
from django.db import models
class Model1(models.Model):
title = models.CharField(max_length=20)
def __str__(self):
return self.title
class Model2(models.Model):
title = models.CharField(max_length=20)
models1 = models.ManyToManyField(to="Model1")
def __str__(self):
return self.title
}}}
and this admin.py
{{{
from django.contrib import admin
from .models import Model1, Model2
admin.site.register(Model1)
admin.site.register(Model2)
}}}
My test scenario:
1. Add two `Model1` items via admin
2. Add one `Model2` item via admin, choose one instance of `Model1` for
many-to-many field
3. Edit the `Model2` item via admin choosing both `Model1` instances for
many-to-many field
4. Open history for `Model2` instance
5. "No fields changed." is in history even though we have changed one of
the fields.
I guess that this could be caused by lazy evaluation of initial queryset.
Initial data is loaded from model instance using `model_to_dict` which
calls `f.value_from_object` for each field. `ManyToManyField` implemention
returns a queryset. It think it is only evaluated when object history
messages are constructed, i.e., after object is saved to database, and
queryset returns already saved values instead of initial values. Because
of this, initial and saved data are always the same and this field never
appears in `changed_data`.
I was able to reproduce this on 1.11.2.
--
Ticket URL: <https://code.djangoproject.com/ticket/28301>
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