Matching query does not exist after a post_data signal, but in fact does exist when visiting the url sent by the query

[François-Xavier Cao]

Hi everone,

I started to code a two-apps django project. ModelA belongs to appone and ModelB belongs to apptwo. My purpose is to create a ModelA instance everytime that the user creates a ModelB instance. And the value of a ModelA CharField (that is ckeditor widgeted) must be the source code of a ModelB admin view. I used a post_data signal to link a function of creation for that. The problem is that i use the id of each instance of ModelB in order to create the good content for each instance of ModelA. When I try to use a string of the url sending the id parameter, the content field has for value the source code of the debug page

(error 500, DoesNotExist at /admin/apptwo/modelb/my_view/ref=76, [76 is an example] ModelB matching query does not exist. Exception location : /home/me/Desktop/env/lib/python3.5/site-packages/django/db/models/query.py in get, line 385)

But when I try to visit the url "http://localhost:8000//admin/apptwo/modelb/my_view/ref=76", or when I hardcode the url, without a str(instance.id), the page exists and everything works perfectly.

I don't understand why.

Could anybody give me some help to solve this problem ?

Thanks in advance,

---

PS :

The first app has a model.py that contains the following code :

from django.db import models
from django.contrib.auth.models import User
from registre.models import *

class ModelA(models.Model):
    content = models.CharField(max_length=255, null=True)
    def __str__(self):
        return "ModelA : " + str(self.id)

the admin.py of this first app also contains :

from django.contrib import admin
from appone.models import *
from apptwo.models import ModelB
from django.http import HttpResponse
from django.template.response import TemplateResponse
from django.conf.urls import url
from registre import views
from django.db.models.signals import post_save
from django.dispatch import receiver
import datetime
from django.contrib.auth.models import User
from django import forms
from ckeditor.widgets import CKEditorWidget
from django.template.loader import render_to_string
import requests

class ModelAAdminForm(forms.ModelForm):
    content = forms.CharField(widget=CKEditorWidget())
    class Meta:
        model = ModelA
        fields = '__all__'

class ModelAAdmin(admin.ModelAdmin):
    form = ModelAAdminForm

def create_A(sender, instance, **kwargs):
    string = "http://localhost:8000/admin/apptwo/modelb/my_view/ref=" + str(instance.id)
    r = requests.get(string)
    ModelA.objects.create(contenu=r.text.encode('utf-8'))

post_save.connect(create_A, sender=ModelB) 

admin.site.register(ModelA, ModelAAdmin)

the second app (apptwo) has a models.py like this :

from django.db import models
from django.contrib.auth.models import User

class ModelB(models.Model):
    owner = models.ForeignKey(User, null=True)
    name = models.CharField(max_length=255, null=True)

    def __str__(self):
        return self.name

and an admin.py that contains :

    from django.contrib import admin
    from appone.models import *
    from apptwo.models import *
    import datetime
    from django.conf.urls import url, include
    from django.template.response import TemplateResponse

    class ModelBAdmin(admin.ModelAdmin):

        def get_queryset(self, request):
            qs = super(ModelB, self).get_queryset(request)
            if request.user.is_superuser:
                return qs
            return qs.filter(owner=request.user)

        def save_model(self, request, obj, form, change):
            obj.owner = request.user
            obj.save()

        def get_urls(self):
            urls = super(ModelBAdmin, self).get_urls()
            my_urls = [
                url(r'^my_view/ref=(?P<id>\d+)$', self.my_view),
            ]
            return my_urls + urls

        def my_view(self, request, id):
            context = dict(
               self.admin_site.each_context(request),
               selector = ModelB.objects.get(id=id),
            )
            return TemplateResponse(request, "myview.html", context)

admin.site.register(ModelB, ModelBAdmin)

and finally a template myview.html with :

<p>Test {{ selector.name }}</p>

[Constantine Covtushenko]

Hi, François-Xavier

I believe that the reason of that is a transaction that is not committed yet  when your code reaches 'post_save' listener.

And when you use 'requests' library there is nothing in the DB yet.

And I am just curios why there is a need of saving 'admin view' in the DB?

Regards,

Constantine C.

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Sincerely yours,

Constantine C