postgresql 断言错误：Django-rest-Framework
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Assertion error at: Django-rest-Framework
提问by DanielTheRocketMan
I am using python 3.4, Django 1.7.1 (the version considered in the book), Postgres 9.3 and my IDE is Eclipse.
我使用的是 python 3.4、Django 1.7.1（书中考虑的版本）、Postgres 9.3，我的 IDE 是 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,
我一直在学习“轻量级 Django - Elman 和 Lavin”这本书，我在第 4 章和第 5 章被困了好几天，我们应该在那里使用其余框架和backbone.js。参见例如，
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:
几天前，我尝试按照书中介绍的方式通过 myseld 进行编码，并检查上面链接中提供的示例。但是，由于我没有继续，我决定复制上面链接中提供的代码并尝试运行。出现了同样的错误：
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 querysetargument, or set read_only=True.
关系字段必须提供queryset参数，或设置 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):
这个错误出现在“relations.py，它属于 django-rest-framework。由于我使用的是上面链接中提供的确切代码，它应该没有错误。实际上，我更改的唯一一段代码在settings.py中（在错误反复发生之后）：
Before:
前：
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.postgresql_psycopg2',
'NAME': 'scrum',
}
}
Now:
现在：
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:
如下所示，我的用户“daniel”具有以下属性：
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
最后，我似乎对 psycopg2 的安装没有任何问题，因为我能够创建如下所示的“scrum”。事实上，我的系统的数据库列表是
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?
有人可以帮我发现问题吗？
回答by Aldarund
Read the DRF docs here.
在此处阅读 DRF 文档。
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.
在版本 2.xa 中，如果使用 ModelSerializer 类，序列化器类有时可以自动确定查询集参数。
此行为现在被替换为始终对可写关系字段使用显式查询集参数。
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.
您只是使用比所用代码作者更新的 DRF 版本，因此您需要使用较低版本或修复代码。
In serializers.pythere's this line:
在serializers.py 中有这一行：
assigned = serializers.SlugRelatedField(slug_field=User.USERNAME_FIELD, required=False)
You need to either add read_only=Trueor queryset=User.objects.all()
您需要添加read_only=True或queryset=User.objects.all()
