Use DeriveEntityModel without having a Relation enum

[LasseRosenow]

Summary

Right now, when I use the DeriveEntityModel Derive Macro, I need to have a enum Relation, which derives DeriveRelation.
Otherwise I get the error: cannot find type Relation in this scope.

Motivation

The reason why I would like to use the DeriveEntityModel macro without having the Relation enum is because I don't use the Relation enum.

I like to define my relations like this:

impl Related<super::homes::Entity> for Entity {
    fn to() -> RelationDef {
        Entity::belongs_to(super::homes::Entity)
            .from(Column::HomeId)
            .to(super::homes::Column::Id)
            .into()
    }
}

So there really is no need and it works... Right now I just have an empty Relation enum and that just feels a bit useless and adds unnecessary clutter.

[billy1624]

Hey @LasseRosenow, welcome! Take the entity below as an example, you're saying that you want to get rid of the empty Relation Enum completely?

use sea_orm::entity::prelude::*;
use serde::{Deserialize, Serialize};

#[derive(Clone, Debug, PartialEq, DeriveEntityModel, Deserialize, Serialize)]
#[sea_orm(table_name = "posts")]
pub struct Model {
    #[sea_orm(primary_key)]
    #[serde(skip_deserializing)]
    pub id: i32,
    pub title: String,
    #[sea_orm(column_type = "Text")]
    pub text: String,
}

#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
pub enum Relation {}

impl ActiveModelBehavior for ActiveModel {}

[LasseRosenow]

@billy1624 yes. As far as I understand, I don't really need the Relation enum because all relations between entities are created by using the related<> trait.

So I didn't like to have things at multiple places so I got rid of all the stuff inside the Relation enum and moved it inside the related traits.

So long answer short: yes I would like not to have those empty structures that I don't use, but if there are technical reasons as to why they need to exist, that would okay too of course :)

[LasseRosenow]

This all of course would not be necessary if the Relation enum derive macro would work as documented.

See this screenshot from the documentation says that the whole first code block could be replaced by the one at the bottom which is using the macro, but I could not reproduce this.

When I only used the lower one with the macro, I still had to write the related<> traits as well. Is this a bug, or is the documentation wrong about that the enum with the macro replaces everything above?

Because if I could specify all my relations just with the Relation enum using macros, that would be cool as well and a good alternative to getting rid of the enum and doing everything with the related<> trait and there would be less boilerplate as well

[tyt2y3]

The macro annotation only handles the impl of the RelationTrait but not the Related trait.
And your usage is perfectly fine, and yes you probably don't need the empty enum.
I think in order for us to properly support that, we'd depend on https://rust-lang.github.io/rfcs/2532-associated-type-defaults.html (rust-lang/rust#29661)