HasManyThrough using HasMany

[clayrisser]

This pull request attempts to set up the hasManyThrough relation using the hasMany relation. It does it using a through property that can be provided to the @hasMany() decorator.

I chose to setup the hasManyThrough this way in an attempt to stick to the existing loopback hasManyThrough spec.

https://loopback.io/doc/en/lb3/HasManyThrough-relations.html#defining-a-hasmanythrough-relation

import { Entity, model, hasMany, property } from '@loopback/repository';
import { Patient, Appointment } from '../models';

@model()
export class Physician extends Entity {
  @property({
    type: 'string',
    id: true
  })
  id?: string;

  @hasMany(() => Patient, { through: () => Appointment })
  patients: Patient[];
}

See also #2264
See also #2356

Checklist

• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• API Documentation in code was updated
• Documentation in /docs/site was updated
• Affected artifact templates in packages/cli were updated
• Affected example projects in examples/* were updated

[clayrisser]

I've separated the hasMany and hasManyThrough repository factories. Please reference the following two comments.

#2264 (comment)

#2264 (comment)

[bajtos]

@codejamninja thank you for the pull request, this is great effort!

I'll need to set aside larger chunk of time to review the changes, hopefully later this week 🤞

I've separated the hasMany and hasManyThrough repository factories.

Please add integration-level tests for the new repository factory to https://github.com/strongloop/loopback-next/blob/master/packages/repository/src/__tests__/integration/repositories/relation.factory.integration.ts

I think we should also copy https://github.com/strongloop/loopback-next/blob/master/packages/repository/src/__tests__/acceptance/has-many.relation.acceptance.ts into has-many-through.relation.acceptance.ts and write tests to cover the new "through" mode.

[clayrisser]

Ok, thanks @bajtos

[clayrisser]

I just added integration level tests and acceptance tests. They are all passing for me.

[clayrisser]

Anyone wanting to get early access to the hasManyThrough relation (or anyone wanting to test it), you can install it the following way.

npm install --save @loopback/repository@git+https://[email protected]/codejamninja/loopback-next.git#npm/has-many-through

or add the following to your package.json file

{
  "dependencies": {
    "@loopback/repository": "git+https://[email protected]/codejamninja/loopback-next.git#npm/has-many-through"
  }
}

[clayrisser]

I just added some basic usage docs for hasManyThrough

[raymondfeng]

@codejamninja Thank you for the contribution. I'll try to find some time to go over the PR.

[bajtos]

Great start, @codejamninja!

I like @hasMany(() => Customer, {through () => Order}) API and also the repository APIs as used by relation consumers (e.g. in Controllers) 👍

However, I feel we need to rework and improve the design and the interactions between the repository factory, the has-many-through constrain and HasManyThroughRepository, PTAL at my last comment below.

[TomerSalton]

Hey,
I wanted to ask what is the difference in the functionality (not implementation) between hasManyThrough and hasAndBelongsToMany?

Edit:
Shouldn't we add a function 'findSourceByTargetID'?

[bajtos]

I wanted to ask what is the difference in the functionality (not implementation) between hasManyThrough and hasAndBelongsToMany?

This is my understanding:

• hasManyThrough requires the user to explicitly provide the "through" (junction) model.
• hasAndBelongsToMany creates the "through" model automatically for the user.

@raymondfeng is that correct?

[TomerSalton]

I wanted to ask what is the difference in the functionality (not implementation) between hasManyThrough and hasAndBelongsToMany?

This is my understanding:

• hasManyThrough requires the user to explicitly provide the "through" (junction) model.
• hasAndBelongsToMany creates the "through" model automatically for the user.

@raymondfeng is that correct?

You are right in that aspect. What about the API though?

[bajtos]

What about the API though?

I think that's something we need to find out while working on hasAndBelongsToMany relation. Do you anticipate any problems if we don't consider hasAndBelongsToMany requirements while working on hasManyThrough? If not, then let's move discussion about hasAndBelongsToMany to a more appropriate place please, to keep this PR focused on hasManyThrough.

[clayrisser]

I don't anticipate any problems.

[bajtos]

@codejamninja what's the status of this pull request? Do you need any additional information or feedback from us? I just want to ensure the progress is not blocked by us.

[clayrisser]

@bajtos, thanks for asking. I am not blocked. The holdup is my schedule. I should get back to this sometime towards the end of the week.

[ckoliber]

When this feature will merge to master ?

At the moment, this work is a community effort. @KalleV was kind enough to contribute the first step - see #4247.

Would you @koliberr136a1 like to join the forces and help @KalleV with the next steps?

I like a lot, but unfortunately I haven't the required informations about how to implement this feature

[MacGyver26]

Hello guys !

Do you know when this feature is going to be available in the framework ? thanks in advance.

[dhmlau]

@MacGyver26, I believe #4438 takes over the implementation of the hasManyThrough relation.

[agnes512]

The implementation and documentation are merged, closing the issue.