fix(belongsTo): set related many set correct relationships

src/Orm/Relations/BelongsTo.ts

@@ -194,19 +194,10 @@ export class BelongsTo implements RelationContract {
    * Must be implemented by parent class
    */
   public setRelatedMany (models: ModelContract[], related: ModelContract[]) {
-    /**
-     * Instead of looping over the model instances, we loop over the related model instances, since
-     * it can improve performance in some case. For example:
-     *
-     * - There are 10 parentInstances and we all of them to have one related instance, in
-     *   this case we run 10 iterations.
-     * - There are 10 parentInstances and 8 of them have related instance, in this case we run 8
-     *   iterations vs 10.
-     */
-    related.forEach((one) => {
-      const relation = models.find((model) => model[this.foreignKey] === one[this.localKey])
+    models.forEach((model) => {
+      const relation = related.find((one) => one[this.localKey] === model[this.foreignKey])
       if (relation) {
-        this.setRelated(relation, one)
+        this.setRelated(model, relation)
       }
     })
   }

test/orm/model-belongs-to.spec.ts

@@ -174,10 +174,53 @@ test.group('Model | Belongs To', (group) => {
       public user: User
     }
 
+    await db.insertQuery().table('users').insert([{ username: 'virk' }])
+
+    const users = await db.query().from('users')
+    await db.insertQuery().table('profiles').insert([
+      {
+        user_id: users[0].id,
+        display_name: 'virk',
+      },
+      {
+        user_id: users[0].id,
+        display_name: 'virk',
+      },
+    ])
+
+    const profiles = await Profile.query().preload('user')
+    assert.instanceOf(profiles[0].user, User)
+    assert.instanceOf(profiles[1].user, User)
+  })
+
+  test('preload belongsTo relationship for many rows', async (assert) => {
+    class User extends BaseModel {
+      @column({ primary: true })
+      public id: number
+    }
+
+    class Profile extends BaseModel {
+      @column({ primary: true })
+      public id: number
+
+      @column()
+      public userId: number
+
+      @column()
+      public displayName: string
+
+      @belongsTo(() => User)
+      public user: User
+    }
+
     await db.insertQuery().table('users').insert([{ username: 'virk' }, { username: 'nikk' }])
 
     const users = await db.query().from('users')
     await db.insertQuery().table('profiles').insert([
+      {
+        user_id: users[0].id,
+        display_name: 'virk',
+      },
       {
         user_id: users[0].id,
         display_name: 'virk',
@@ -188,8 +231,10 @@ test.group('Model | Belongs To', (group) => {
       },
     ])
 
-    const profile = await Profile.query().preload('user').where('display_name', 'virk').first()
-    assert.instanceOf(profile!.user, User)
+    const profiles = await Profile.query().preload('user')
+    assert.equal(profiles[0].user.id, 1)
+    assert.equal(profiles[1].user.id, 1)
+    assert.equal(profiles[2].user.id, 2)
   })
 
   test('raise exception when foreign key is not selected', async (assert) => {