Import column from another table - django

Question

I made API with Django Restframework.
[models.py]
from django.db import models
class Article(models.Model):
article_no = models.AutoField(primary_key=True)
content = models.CharField(max_length=500, null=False)
password = models.CharField(max_length=20, null=False, default='1234')
date = models.DateTimeField(auto_now_add=True)
class Comment(models.Model):
article_no = models.ForeignKey('Article', on_delete=models.CASCADE)
content = models.CharField(max_length=50, null=False, default='')
password = models.CharField(max_length=20, null=False, default='1234')
date = models.DateTimeField(auto_now_add=True)
[views.py]
class ArticleDetail(APIView):
def get(self, request, article_no, format=None):
try:
article = models.Article.objects.get(article_no=article_no)
serializer = serializers.ArticleDetailSerializer(article)
return Response(status=status.HTTP_200_OK, data=serializer.data)
except models.Article.DoesNotExist:
return Response(status=status.HTTP_404_NOT_FOUND)
[urls.py]
urlpatterns = [
path('article/<int:article_no>', views.ArticleDetail.as_view(), name='article_detail'),
]
[serializers.py]
class ArticleDetailSerializer(serializers.ModelSerializer):
password = serializers.CharField(write_only=True, required=True)
comment = CommentSerializer(many=True, read_only=True)
class Meta:
model = models.Article
fields = (
'article_no',
'content',
'password',
'date',
'comment',
)
In serializers.py, I defined comment = CommentSerializer(many=True, read_only=True) and add it to fields.
And to test it, I add comment for article_no=1
But When I connect to /article/1, comment doesn't show anything.
I want to show all comments related it's article_no.
How can I fixed it?
Thanks.
Fixed source is here.
[serializers.py]
class ArticleDetailSerializer(serializers.ModelSerializer):
password = serializers.CharField(write_only=True, required=True)
class Meta:
model = models.Article
fields = (
'article_no',
'content',
'password',
'date',
'comments',
)
[models.py]
class Comment(models.Model):
article_no = models.ForeignKey(Article, on_delete=models.CASCADE, related_name='comments')
content = models.CharField(max_length=50, null=False, default='')
password = models.CharField(max_length=20, null=False, default='1234')
date = models.DateTimeField(auto_now_add=True)
When I connect to my server,
It only shows related comment's article_no.
But I want to show content and date also.

Answer 1

According to the Django documentation at https://docs.djangoproject.com/en/2.0/topics/db/queries/#backwards-related-objects you can access the list of objects by calling article_instance.comment_set.all() or you could set the related_name argument on the model on initialization
article_no = models.ForeignKey('Article', on_delete=models.CASCADE, related_name="comments")
and access is like article_instance.comments.all() or filter() or exclude()
There are quite a few options actually, and it depends on the use case, but for simplicity, in this case you may be able to just change the comment variable to comment_set, or you could change the related_name to comments and refer to it as such in your serializer.
required changes to ArticleDetailSerializer...
comment = CommentSerializer(many=True, read_only=True)
to
comments = CommentSerializer(many=True, read_only=True)
You also haven't created a CommentSerializer class, or you haven't posted it to the question.
example CommentSerializer....
class CommentSerializer(serializers.ModelSerializer):
class Meta:
model=Comment
exclude=('article_no',)
I exclude the article_no and the remaining fields should be handled due to the assigned defaults on the django models.
The related object manager in Django returns a queryset that can be acted on like any other queryset. So you will want to consider whether an article might have an absurd amount of comments and limit the returned amount.
you can also use a SerializerMethodField and have more control over the returned queryset
comments = serializers.SerializerMethodField()
def get_comments(self, obj):
comments = obj.comments/comment_set.all()[:20] #return the first 20 comments
return CommentSerializer(comments/comment_set, many=True, read_only=True).data
now add comments/comment_set to the class Meta/fields tuple