diesel-rust (Postgres) with uuid failing, E0277 diesel::Expression is not satisfied

Question

I am porting an existing Python/SQLAlchemy app to rust. I'm totally new to rust and it seems like diesel is a reasonable replacement for SQLAlchemy (I also need to do postgis, and diesel seems to be the only rust ORM that has anything for that).

Simple demo of code is on github diesel_uuid. Based on the posts here and here, I have dependencies:

uuid = { version = "0.8.2", features = ["serde", "v4"] }
diesel = { version = "2.1.0", features = ["chrono", "postgres", "r2d2", "uuid"] }

It builds and runs, but I'm having problems with the UUID type.

In my src/bin/get_user.rs code I have:

    let real_uid = Uuid::parse_str( &id );

    let results = uuid_users
               .filter( user_uid.eq( real_uid ) )
               .limit(5)
               .select(models::UuidUser::as_select())
               .load(connection)
               .expect("Error loading users");

If I try and build this I get:

error[E0277]: the trait bound Result<uuid::Uuid, uuid::Error>: diesel::Expression is not satisfied
 --> src/bin/get_user.rs:19:20
   |
19 |     .filter( user_uid.eq( real_uid ) )
   |                       ^^ the trait diesel::Expression is not implemented for Result<uuid::Uuid, uuid::Error>
   |

And then a bunch more errors. If I filter on the String column (name) instead, it works just fine, so the code works - just not the uuid filter.

Based on the other posts about diesel and uuid, I'm wondering if I'm doing something wrong w.r.t. diesel and uuid versioning? Or maybe some use ordering of the use and mod lines?

Answer 1

Arrrgggh....

Uuid::parse_str returns a Result<Uuid, Error>. Calling .unwrap() on it fixes the problem.

Credit to Ross Rogers for the fix.