Implement diesel::Expression and other necessary traits for std::rc::Rc<T> where T: Expression

[LucaCappelletti94]

Hi,

I work on an rust monolithic open source research project where we employ diesel both for the frontend and backend. In the frontend, we employ the yew framework, which as other web frameworks employs Rc to share non-copiable objects without cloning across the web components.

Since we create our core structures only once and reuse them thorough across the project in an effort to maximize code re-usability and minimize code duplication, we would like to wrap non-copiable attributes such as String with an Rc.

This means for instance that the following struct:

#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(
    diesel::Selectable,
    diesel::Insertable,
    diesel::AsChangeset,
    diesel::Queryable,
    diesel::Identifiable,
)]
#[cfg_attr(feature = "yew", derive(yew::prelude::Properties))]
#[diesel(primary_key(id))]
#[diesel(
    table_name = crate::codegen::diesel_codegen::tables::login_providers::login_providers
)]
pub struct LoginProvider {
    pub id: i16,
    pub name: String,
    pub icon: String,
    pub client_id: String,
    pub redirect_uri: String,
    pub oauth_url: String,
    pub scope: String,
}

would be turned into:

#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(
    diesel::Selectable,
    diesel::Insertable,
    diesel::AsChangeset,
    diesel::Queryable,
    diesel::Identifiable,
)]
#[cfg_attr(feature = "yew", derive(yew::prelude::Properties))]
#[diesel(primary_key(id))]
#[diesel(
    table_name = crate::codegen::diesel_codegen::tables::login_providers::login_providers
)]
pub struct LoginProvider {
    pub id: i16,
    pub name: std::rc::Rc<String>,
    pub icon: std::rc::Rc<String>,
    pub client_id: std::rc::Rc<String>,
    pub redirect_uri: std::rc::Rc<String>,
    pub oauth_url: std::rc::Rc<String>,
    pub scope: std::rc::Rc<String>,
}

which of course, at the time of writing, does not satisfy the necessary diesel traits.

I believe it would be desirable to proceed to implement these traits in diesel for the std::rc::Rc<T> where T: Expression. If you agree, I will proceed with a PR adding this feature.

Thank you for your time,
Luca

[weiznich]

Sounds reasonable to do. I'm happy to accept a PR that adds impls for Arc and Rc similar to what's already there for Box:

diesel/diesel/src/expression/mod.rs

Line 166 in 325b926

impl<T: Expression + ?Sized> Expression for Box<T> {

That should also include any other trait that provides an impl for Box, which are likely any super trait of BoxableExpression + that trait itself. I think both Arc and Box can essentially copy the trait implementations for Box.

[LucaCappelletti94]

Great to hear, I will make the PR later today!