Impl a generic trait with generic fn, need help

[Martichou]

Hey everyone,

I'm trying to implement a generic trait for diesel. This trait would contains some function definition that needs to be implemented for struct implementing the trait and some function ready-to-use as they would be generic.

I'm having an issue with the exists generic function implementation. More specifically, the filter part is what's not working.
For context, here's the current state of that trait:

use diesel::{
    associations::HasTable, dsl, query_builder::IntoUpdateTarget, query_dsl::methods::{FindDsl, LimitDsl}, sql_types::Bool, Expression
};
use diesel_async::{methods::LoadQuery, AsyncPgConnection, RunQueryDsl};

use crate::{db::utils::PgConn, utils::errors};

type FindId<T> = dsl::Find<<T as HasTable>::Table, <T as CrudId>::IdType>;

pub trait CrudId: HasTable + Sized + Send
where
    Self::Table: FindDsl<Self::IdType>,
    FindId<Self>: LimitDsl + IntoUpdateTarget + Send,
    dsl::Limit<FindId<Self>>: LoadQuery<'static, AsyncPgConnection, Self> + Send + 'static,
{
    type DTOForm;
    type InsertForm<'a>;
    type UpdateForm<'a>;
    type IdType: Send;

    // Unable to impl generic function as it create a real lifetime mess...
    async fn create(new: &Self::InsertForm<'_>, conn: &mut PgConn) -> Result<Self, errors::PError>;

    async fn get_raw_by_id(id: Self::IdType, conn: &mut PgConn) -> Result<Self, errors::PError> {
        Self::table()
            .find(id)
            .first(conn)
            .await
            .map_err(errors::PError::from)
    }

    // Never able to make it works, don't know why but never figured it out
    async fn get_by_id(
        id: Self::IdType,
        conn: &mut PgConn,
    ) -> Result<Self::DTOForm, errors::PError>;

    // Unable to impl generic function as it create a real lifetime mess...
    async fn update(
        id: Self::IdType,
        form: &Self::UpdateForm<'_>,
        conn: &mut PgConn,
    ) -> Result<Self::DTOForm, errors::PError>;

    async fn exists<F>(
        filter: F,
        conn: &mut PgConn,
    ) -> Result<bool, errors::PError>
    where
        F: FnOnce(&Self::Table) -> Box<dyn Expression<SqlType = Bool> + Send>,
    {
        use diesel::QueryDsl;

        let table = Self::table();
        let condition = filter(&table);
        diesel::select(diesel::dsl::exists(table.filter(condition)))
            .get_result::<bool>(conn)
            .await
            .map_err(errors::PError::from)
    }
}

And the error I'm getting doesn't really help.. see:

error[E0275]: overflow evaluating the requirement `_: std::marker::Sized`
  --> src/traits/crud_id.rs:53:50
   |
53 |         diesel::select(diesel::dsl::exists(table.filter(condition)))
   |                                                  ^^^^^^
   |
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`my_diesel_generic_trait`)
   = note: required for `<<Self as HasTable>::Table as AsQuery>::Query` to implement `FilterDsl<_>`

For more information about this error, try `rustc --explain E0275`.

Any help would be appreciated :)