Add index to RelationOptions

Issue type:

[ ] question [ ] bug report [x] feature request [ ] documentation issue

Database system/driver:

[ ] cordova [ ] mongodb [ ] mssql [ ] mysql / mariadb [ ] oracle [x] postgres [ ] sqlite [ ] sqljs [ ] react-native [ ] expo

TypeORM version:

[x] latest [ ] @next [ ] 0.x.x (or put your version here)

Steps to reproduce or a small repository showing the problem:

It would be nice to be able to define in a relation to automatically create an index for it. I think that the best place to put it would in the RelationOptions.

Today it is possible to get the desired result doing the following:

import {Entity, PrimaryGeneratedColumn, Column, ManyToOne, Index} from "typeorm";
import {User} from "./User";

@Entity()
export class Photo {
    
    @PrimaryGeneratedColumn()
    id: number;
    
    @ManyToOne(type => User, user => user.photos)
    user: User;

    @Index
    @RelationId((user: User) => user.photos)
    userId: number;
}

The idea was to be able to do the same with the following code:

import {Entity, PrimaryGeneratedColumn, Column, ManyToOne, Index} from "typeorm";
import {User} from "./User";

@Entity()
export class Photo {
    
    @PrimaryGeneratedColumn()
    id: number;
    
    @ManyToOne(type => User, user => user.photos, { index: true })
    user: User;
}

[pleerock]

indices have high cost, and should be used carefully, we can’t decide for users if they should pay for it on each relation or not. They should decide it on their own.

[leonidasv]

For those who may be struggling with the same issue, I’ve managed to make it work by adding the @Index() decorator right to the relation and removing it from the RelationId:

   @Index()
   @ManyToOne(type => User, user => user.photos)
   user: User;

   @RelationId((photo: Photo) => photo.user)
   userId: number;

It generated the migration:

queryRunner.query(`CREATE INDEX "IDX_dddc92fd77a1b1682a8d6fb07d" ON "photo" ("userId")`)

(the hash after IDX_ is illustrative)