Keep a relation map in Objection.js while removing the table - sql

Question

I'm developing a reddit-like site where votes are stored per-user (instead of per-post). Here's my relevant schema:
content
id | author_id | title | text
---|-----------|-------------|---
1 | 1 (adam) | First Post | This is a test post by adam
vote: All the votes ever voted by anyone on any post
id | voter_id | content_id | category_id
---|-------------|------------------|------------
1 | 1 (adam) | 1 ("First Post") | 1 (upvote)
2 | 2 (bob) | 1 ("First Post") | 1 (upvote)
vote_count: Current tally ("count") of total votes received by a post by all users
id | content_id | category_id | count
---|------------------|--------------|-------
1 | 1 ("First Post") | 1 (upvote) | 2
I've defined a voteCount relation in Objection.js model for the content table:
class Content extends Model {
static tableName = 'content';
static relationMappings = {
voteCount: {
relation: Model.HasManyRelation,
modelClass: VoteCount,
join: {
from: 'content.id',
to: 'vote_count.content_id'
}
}
}
}
But I recently (learned and) decided that I don't need to keep (and update) a separate vote_count table, when in fact I can just query the vote table and essentially get the same table as a result:
SELECT content_id
, category_id
, COUNT(*) AS count
FROM vote
GROUP
BY content_id
, category_id
So now I wanna get rid of the vote_count table entirely.
But it seems that would break my voteCount relation since there won't be a VoteCount model (not shown here but it's the corresponding the model for the vote_count table) no more either. (Right?)
How do I keep voteCount relation while getting rid of vote_count table (and thus VoteCount model with it)?
Is there a way to somehow specify in the relation that instead of looking at a concrete table, it should look at the result of a query? Or is it possible to define a model class for the same?
My underlying database in PostgreSQL if that helps.

Answer 1

Thanks to #Belayer. Views were exactly the solution to this problem.
Objection.js supports using views (instead of table) in a Model class, so all I had to do was create a view based on the above query.
I'm also using Knex's migration strategy to create/version my database, and although it doesn't (yet) support creating views out of the box, I found you can just use raw queries:
module.exports.up = async function(knex) {
await knex.raw(`
CREATE OR REPLACE VIEW "vote_count" AS (
SELECT content_id
, category_id
, COUNT(*) AS count
FROM vote
GROUP
BY content_id
, category_id
)
`);
};
module.exports.down = async function(knex) {
await knex.raw('DROP VIEW "vote_count";');
};
The above migration step replaces my table vote_count for the equivalent view, and the Objection.js Model class for it (VoteCount) worked as usual without needing any change, and so did the relation voteCount on the Content class.