Reuse preloaded lazy relations

[StrikeForceZero]

Issue type:

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

Database system/driver:

[x] all?
[ ] cordova
[ ] mongodb
[ ] mssql
[ ] mysql / mariadb
[ ] oracle
[ ] 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:

import { Note } from './note';

@TypeOrm.Entity()
export class Person {
    @TypeOrm.PrimaryGeneratedColumn()
    public id: number;

    @TypeOrm.Column()
    public name: string;

    @TypeOrm.OneToMany(type => Note, note => note.owner, { lazy: true })
    public notes: Promise<Note[]> | Note[];
}

import { Person } from './person';

@TypeOrm.Entity()
export class Note {
    @TypeOrm.PrimaryGeneratedColumn()
    public id: number;

    @TypeOrm.Column()
    public label: string;

    @TypeOrm.ManyToOne(type => Person, { lazy: true })
    public owner: Promise<Person> | Person;
}

const repoPerson = connection.getRepository(Person);
const repoNote = connection.getRepository(Note);

const personA  = await repoPerson.create({ name: 'personA' });
const personB    = await repoPerson.create({ name: 'personB' });

await repoPerson.save([
        personA,
        personB,
])

await repoNote.insert({ label: 'note1', owner: personA });
await repoNote.insert({ label: 'note2', owner: personB });

const res = await repoPerson.find({ relations: [ 'notes' ] });
console.log(res);
console.log(await res[ 0 ].notes);

results:

query: SELECT "Person"."id" AS "Person_id", "Person"."name" AS "Person_name", "Person_notes"."id" AS "Person_notes_id", "Person_notes"."label" AS "Person_notes_label", "Person_notes"."ownerId" AS "Person_notes_ownerId" FROM "person" "Person" LEFT JOIN "note" "Person_notes" ON "Person_notes"."ownerId"="Person"."id"
[ Person { id: 1, name: 'personA', __notes__: [ [Object] ] },
  Person { id: 2, name: 'personB', __notes__: [ [Object] ] } ]
query: SELECT "notes"."id" AS "notes_id", "notes"."label" AS "notes_label", "notes"."ownerId" AS "notes_ownerId" FROM "note" "notes" WHERE "notes"."ownerId" IN (?) -- PARAMETERS: [1]
[ Note { id: 1, label: 'note1' } ]

I'd expect it to reuse the relationship that was preloaded instead of reselecting:

query: SELECT "Person"."id" AS "Person_id", "Person"."name" AS "Person_name", "Person_notes"."id" AS "Person_notes_id", "Person_notes"."label" AS "Person_notes_label", "Person_notes"."ownerId" AS "Person_notes_ownerId" FROM "person" "Person" LEFT JOIN "note" "Person_notes" ON "Person_notes"."ownerId"="Person"."id"
[ Person { id: 1, name: 'personA', __notes__: [ [Object] ] },
  Person { id: 2, name: 'personB', __notes__: [ [Object] ] } ]
[ Note { id: 1, label: 'note1' } ]

PR #2966