Using raw sql to get structs not related to any table schema

[hweom]

Imagine I have the following schema:

table! {
    records (id) {
        id -> Int8,
        record_type -> Int2,
        amount -> Numeric,
        price -> Numeric,
    }
}

And I want to execute some aggregating query like this:

#[derive(QueryableByName)]
struct Entry {
    #[sql_type = "Integer"]
    record_type: i32,
    #[sql_type = "Numeric"]
    value: f64,
}

fn main() {
    let database_url = env::var("DATABASE_URL").expect("DATABASE_URL must be set");
    let connection = PgConnection::establish(&database_url).unwrap();
    
    let query = "SELECT record_type, sum(price * amount) as value from records";
    let results = sql_query(query).load::<Entry>(&connection);
}

But this gives me an error:

error[E0277]: the trait bound `diesel::query_builder::SqlQuery: diesel::query_dsl::LoadQuery<_, Entry>` is not satisfied
  --> src/main.rs:25:36
   |
25 |     let results = sql_query(query).load::<Entry>(&connection);
   |                                    ^^^^ the trait `diesel::query_dsl::LoadQuery<_, Entry>` is not implemented for `diesel::query_builder::SqlQuery`
   |
   = help: the following implementations were found:
             <diesel::query_builder::SqlQuery as diesel::query_dsl::LoadQuery<Conn, T>>

Is there something that I'm missing?

[hweom]

Ugh, found the reason. diesel::sql_types::Numeric cannot be converted into f64, only into BigDecimal.

The error is quite misleading tho.

[sgrif]

We don't have any control over the error Rust generates here.