AdonisJS 5 - preload model even if foreign key is null

Question

I want to preload a model even if it have a null foreign key. I'll use the models from Adonis docs page to ilustrate: User and Profile.

const user = await User.query().preload("profile")

Simple as that!

But in my case, if a user have the key profile_id as null, it throws an exception, what means it only preload existing relationships (fair enough).

To make clear, I not want to preload just users with existing foreign keys, I need both existing user related models and users with no models to preload.

I have read and tested the examples from docs page, but it haven't enough explanation about this case (or I just didn't found it).

Any hints will be appreciated

Answer 1

Let me first answer your question, YES, you can preload Fk which are NULL.

PS - you have not given any details apart from the query, so i am going to make some assumptions.

Explanation-

1. First you have to define relationship before using preload
2. Relationsgip should be defined in the table which contains FK, in our case, its User table. e.g

//User.ts or User.js
import Profile from '/path/to/profile';

...
  @column()
  public profileId: number;

  @belongsTo(() => Profile)
  public profile: BelongsTo<typeof Profile>;
...

As you can see, i have created a relationship in user table. i.e

  @belongsTo(() => Profile)
  public profile: BelongsTo<typeof Profile>;

Once this is done, you can query user and preload profile.

const user = await User.query().preload("profile")

Now, if the user has profile, then it will be preloaded (join), and output will be something like this

User {
 id: <random-number>,
 profileId: <random-number>,
 profile: {
  ...
 },
 ...
}

in case, profileId is null, then output will be something like this

User {
 id: <random-number>,
 profileId: null,
 ...
}

ps - user variable is an array of User instance and i have given example of just 1 User instance.

I hope this explanation has helped you.