Mikro-orm v6 serialization with em.populate()

[Zmaon]

Hi,

We have a case where we need to use em.populate() to load a lot of field on existing entities in some conditions. Following this change (https://mikro-orm.io/docs/upgrading-v5-to-v6#implicit-serialization-changes), it seems that those fields are not serialized by default, and that we should manually do a wrap().populated() for each of them in order to have them in the output (it's a Nest.js project).

Shouldn't a call to em.populate() automatically add the fields in the serialization? It seems to be a lot of boilerplate to do it manually, when the intent seems quite clear when you populate this way.

Thanks!

Simon

[B4nan]

Shouldn't a call to em.populate() automatically add the fields in the serialization?

It's all driven by the populate hint of the root entity you serialize, if you call em.populate on it, it should work out of box I think. Having that on a child is not enough, the whole point of this is that there need to be one root that knows how the entity graph should look like, otherwise there is no way to properly serialize cycles.

Can you provide some repro so its clear what you are doing?

edit: this is the method responsible for updating the serialization context:

https://github.com/mikro-orm/mikro-orm/blob/master/packages/core/src/entity/EntityLoader.ts#L122C11-L122C34

[Zmaon]

I see. Digging further I think that our issue is only related to serialization, not population.

To go into more detail our problem is that we populate a tree where we can have an arbitrary number of branches. Unfortunately I can't share the code, but if I simplify we have an entity like that:

class Entity {
  @OneToMany(() => Entity, entity => entity.parent)
  children = new Collection<Entity>this);

  @ManyToOne(() => Entity, { nullable: true })
  parent? = Entity;

  @Property({ type: 'varchar', length: 100 })
  name!: string;

  # A bunch of other properties
  ...
}

Before version 6, loading all the entities with a findAll() while populating only the first level was directly returning the whole tree:

 const entities: Entity[] = await this.entitityRepository.findAll({
      populate: [
        'parent',
        'children',
        ...
      ]
  })

# the interface returns the whole tree
return entities

With version 6, it only returns the first level, because of the change on the serialize(). Is there any way to tell the serializer to take everything into account as it was before?

[Zmaon]

Yes, I'm now wondering how it was working so well with the previous version of Mikro-orm.

[Zmaon]

I think the idea of returning a random payload shape is flawed, you should rethink this approach.

Any tree would have this problem if the number of levels is unknown, and trees are pretty common in API answers. In my opinion an ORM shouldn't be too opinionated and it should leave its users the freedom to shape their payloads in the way they want.

This said I understand that the problem is not trivial, and I also think that a predictable output is a good thing. I just wish I had a simple solution for my problem.

[B4nan]

In my opinion an ORM shouldn't be too opinionated and it should leave its users the freedom to shape their payloads in the way they want.

You can shape your payload in any way you want, you can serialize stuff yourself instead of depending on the implicit serialization. This is not about being opinionated, this is about being predictable. You want something else, so you need to provide custom code to do that. The previous implementation wasn't giving users freedom, in my eyes it was the opposite. Check the PR and the issues it closed to have a better understanding of what changed and why.

[Zmaon]

Ok we ended up implementing a custom serialization for the tree.

Thanks a lot for your prompt answers, really appreciated.

[B4nan]

If you can think of something we could add to the ORM toolbelt, I am open for suggestions. Maybe some option (for explicit serialization) to override the function that says if something should be populated or not would do the job?

https://github.com/mikro-orm/mikro-orm/blob/master/packages/core/src/serialization/EntitySerializer.ts#L26