Assertion error at: Django-rest-Framework
backbone.js, django, django-rest-framework, postgresql, python
Solution
Read the DRF docs here.
In version 2.x a serializer class could sometimes automatically determine the queryset argument if a ModelSerializer class was being used.
This behavior is now replaced with always using an explicit queryset argument for writable relational fields.
You are just using a newer version of DRF than the authors of the code used, so you'll need to either use a lower version or fix the code.
In serializers.py there's this line:
assigned = serializers.SlugRelatedField(slug_field=User.USERNAME_FIELD, required=False)
You need to either add `read_only=True` or `queryset=User.objects.all()`
Problem
I am using python 3.4, Django 1.7.1 (the version considered in the book), Postgres 9.3 and my IDE is Eclipse. I have been studying the book "Lightweight Django - Elman and Lavin" and I have been stuck for days in the chapters 4 and 5, where we are supposed to use the rest framework and backbone.js. See for instance, Lightweight Django - Chapters 4 and 5 Some days ago, I tried to code by myseld as presented in the book and also checking with the examples presented in the link above. However, since I was not going ahead, I decided to copy the code presented in the link above and tried to run. The same error has arisen: ``` AssertionError at / Relational field must provide a `queryset` argument, or set read_only=`True`. Request Method: GET Request URL: http://127.0.0.1:8000/ Django Version: 1.7.1 Exception Type: AssertionError Exception Value: ``` Relational field must provide a `queryset` argument, or set read_only=`True`. ``` Exception Location: /usr/local/lib/python3.4/dist-packages/rest_framework/relations.py in __init__, line 35 Python Executable: /usr/bin/python3 Python Version: 3.4.0 Python Path: ['/home/daniel/workspace/Scrum', '/usr/lib/python3.4', '/usr/lib/python3.4/plat-i386-linux-gnu', '/usr/lib/python3.4/lib-dynload', '/usr/local/lib/python3.4/dist-packages', '/usr/lib/python3/dist-packages'] ``` This error arises inside "relations.py, which belongs to the django-rest-framework. Since I am using the exact code presented in the link above, it is supposed to not have errors. Actually, the only piece of code that I changed was in the settings.py (after the error repeatedly happened): Before: ``` DATABASES = { 'default': { 'ENGINE': 'django.db.backends.postgresql_psycopg2', 'NAME': 'scrum', } } ``` Now: ``` DATABASES = { 'default': { 'ENGINE': 'django.db.backends.postgresql_psycopg2', 'NAME': 'scrum', 'USER': 'daniel', 'PASSWORD': '12345', 'HOST': '127.0.0.1', 'PORT': '5432', } ``` As you can see below, my user "daniel" has the following attributes: ``` Role name | Attributes | Member of | Description -----------+------------------------------------------------+-----------+------------- daniel | Superuser, Create DB | {} | postgres | Superuser, Create role, Create DB, Replication | {} | ``` Finally, it seems that I do not have any problem with the installation of psycopg2, since I was able to create "scrum" as presented below. In fact, the list of databases of my system is ``` List of databases Name | Owner | Encoding | Collate | Ctype | Access privileges -----------+----------+----------+-------------+-------------+----------------------- postgres | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | scrum | daniel | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =Tc/daniel + | | | | | daniel=CTc/daniel template0 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres + | | | | | postgres=CTc/postgres template1 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres + | | | | | postgres=CTc/postgres ``` Can someone help me to discover the problem?