How to search through rows and assign column value based on search in Postgres? - django

Question

I'm creating an application similar to Twitter. In that I'm writing a query for the profile page. So when the user visits someone other users profile, he/she can view the tweets liked by that particular user. So for that my query is retrieving all such tweets liked by that user, along with total likes and comments on that tweet.
But an additional parameter I require is whether the current user has liked any of those tweets, and if yes, I want it to retrieve it as boolean True in my query so I can display it as liked in UI.
But I don't know how to achieve this part. Following is a sub-query from my main query
select l.tweet_id, count(*) as total_likes,
<insert here> as current_user_liked
from api_likes as l
INNER JOIN accounts_user ON l.liked_by_id = accounts_user.id
group by tweet_id
Is there an inbuilt function in postgres that can scan through the filtered rows and check whether current user id is present in liked_by_id. If so mark current_user_liked as True, else False.

Answer 1

You want to left outer join back into the api_likes table.
select l.tweet_id, count(*) as total_likes,
case
when lu.twee_id is null then false
else true
end as current_user_liked
from api_likes as l
INNER JOIN accounts_user ON l.liked_by_id = accounts_user.id
left join api_likes as lu on lu.tweet_id = l.tweet_id
and lu.liked_by_id = <current user id>
group by tweet_id
This will continue to bring in the rows you are seeing and will add a row for the lu alias on api_likes. If no such row exists matching the l.tweet_id and the current user's id, then the columns from the lu alias will be null.