Is it possible to implement with Django Restframework? - mysql

Question

I'm making API Server with DRF(DB is MySQL).
Now I made some system similar with facebook's like.
First, below is my Database Structure.
[user table]
userkey(PK)
username
[article table]
articleNo(PK)
userkey(FK to user)
content
[like table]
articleNo
userkey(FK to user)
When user click the "Like" buttons, articleNo and User's key will be inserted into like table.
Currently, When I access to /article/, shows below result.
{
"articleNo": 1,
"userkey": "22222",
"content": "test1",
"date": "2018-02-14T22:34:36.673805+09:00"
},
{
"articleNo": 2,
"userkey": "11111",
"content": "test2",
"date": "2018-02-15T22:34:36.673805+09:00"
},
...
...
If like table has two row like this,
+-----------+---------+
| articleNo | userkey |
+-----------+---------+
| 1 | 11111 |
| 1 | 22222 |
+-----------+---------+
It means that 11111 and 22222 user likes articleNo==1.
So When user access to /article?userkey=11111, What I would like instead as output is something like:
{
"articleNo": 1,
"userkey": "22222",
"content": "test1",
"isLiked": "true", // add this line
"date": "2018-02-14T22:34:36.673805+09:00"
},
{
"articleNo": 2,
"userkey": "11111",
"content": "test2",
"isLiked": "false", // add this line
"date": "2018-02-15T22:34:36.673805+09:00"
},
...
...
Is it possible to implement with DRF?
Thanks.

Answer 1

Yes, this can be done entirely on the ORM level, by using Django 1.8 conditional expressions
Having the following model structure (some example values):
class User(models.Model):
userkey = models.AutoField(primary_key=True)
username = models.CharField(max_length=255)
class Article(models.Model):
articleNo = models.AutoField(primary_key=True)
user = models.ForeignKey(User)
content = models.TextField()
class Like(models.Model):
article = models.ForeignKey(Article)
user = models.ForeignKey(User)
To demonstrate how this works, I created some example data:
john = User.objects.create(userkey=1, username='John')
alice = User.objects.create(userkey=2, username='Alice')
john_article = Article.objects.create(articleNo=1, user=john, content='Hi, I am John!')
alice_article = Article.objects.create(articleNo=2, user=alice, content='Hi, I am John!')
alice_likes_john_article = Like.objects.create(user=alice, article=john_article)
alice_likes_her_article = Like.objects.create(user=alice, article=alice_article)
john_likes_his_article = Like.objects.create(user=john, article=john_article)
You could achieve what you want on the ORM level:
articles = Article.objects.all().annotate(
like_count=Sum(
Case(
When(like__user=john, then=1),
default=0,
output_field=IntegerField(),
)
),
).annotate(
likes=Case(
When(like_count__gt=0, then=True),
default=False,
output_field=BooleanField()
)
)
(If somebody knows a simpler way than the above, I would be happy to learn as well)
Now every Article instance in the articles queryset will have two additional attributes: likes_count with the number of likes an article has received from John, and likes, a boolean, indicating if John likes it or not. Obviously you're interested in the latter.
Just override the get_queryset() method of your Article ViewSet, and then add an additional field to the Serializer of your Article class.
Also, you probably need to somehow pass the user instance (or the id) for the filter, but that can be done in various ways, including (for example) reading the query params inside the get_queryset method.