Separation of concerns with derive attribute

help
1

I am pretty new to rust and trying to design what I feel is cleanish code. I will pick on the diesel crate for my example, but it can apply to any derivable trait.

Say I have an app with a domain.rs file that holds my models, which are just structs. For example:
pub struct Foobar { pub id: String }. I want this file to be pretty clean so I do not put anything else in it, but I want to use these models with the diesel crate, which means I need to implement the Queryable trait for example.

Most examples will use #[derive(Queryable)] on their struct in the same file. But I want to have another file just for my database code, lets call it database.rs. In database.rs i want to implement Queryable for my Foobar struct. I know I can use the impl block to accomplish this, but lets face it I want the benefits of #[derive].

Is there a way to use #[derive(Queryable)] on my Foobar struct in the database.rs file or use the benefits of derive somehow? Are there better designs that may help? I could see wrapping Foobar in a new type (thereby creating "database models"), but I am trying to see if there is a simple solution.

2

There's not really a way to do this. Since derive is like a macro, it operates at the source code level and it actually needs the original source code for the struct definition in order to be able to generate the implementation.

3

Thank you @jethrogb! That saves me a bunch of time crawling round the internet trying to find something.

4

@jethrogb so I am coming back to the app that made me ask this question. How do rust developers typically separate these concerns (database vs domain), or do they? If I look at the "command" side of my application that deals with saving data i see three potential options:

  1. Have one struct that has the diesels derive macros which also implements my my domain logic
  2. Have a database struct that uses diesels derive macro and a domain struct that has the domain logic. Both would have similar properties. I would also have to implement something such as the From trait to map between the two structures when querying and saving.
  3. Manually implement the diesel traits instead of their derive macros on the domain struct