InsertResult to return the primary key's type

[tyt2y3]

Currently, the last_insert_id from InsertResult simply uses the ExecResult's last_insert_id.
However, at least for Postgres with returning, we should be able to retrieve the primary key column for the Entity and return the value in its native type. For example, a uuid instead of an i64.

[billy1624]

How we handle composite primary keys?

[tyt2y3]

Composite primary keys can't be auto generated, and so it's less important. But I think the type could be a tuple, if we really try to support it. Let's leave it and return 0 for now.

[billy1624]

I think this issue can be related to #101 if we have an attribute primary_key. Then, we can derive a struct to represent value of returning columns (primary keys).

[billy1624]

And btw... returning statement in Postgres can return multiple columns at once.
https://www.postgresql.org/docs/current/dml-returning.html

[tyt2y3]

I think for the average case where there is only one column as primary key, adding one container layer is counter intuitive.
But perhaps, we can make an associated type def in the PrimaryKeyTrait

impl PrimaryKeyTrait for PrimaryKey {
    type ValueType = i32;
}

[billy1624]

Adding type def is a good suggestion

[tqwewe]

I've had a dive into the code for this.. it seems like adding ValueType on the PrimaryKeyTrait would work great!
Then perhaps InsertResult can be given a generic:

pub struct InsertResult<T> {
    pub last_insert_id: T,
}

And exec on Insert could return the value type as the generic type:

impl Future<
  Output = Result<InsertResult<<A::Entity as EntityTrait>::PrimaryKey::ValueType>, DbErr>
>

This what I'm thinking would be the best way..

[tyt2y3]

Agreed.