Rust Diesel，加载来自多个表的 select 列的 sql_query 的结果时出错

Question

I tried to execute an sql_query with Diesel that doesn't match a single table and I got the following error:

    error[E0277]: the trait bound `Untyped: load_dsl::private::CompatibleType<TimeCountSumaryEntry, _>` is not satisfied
        --> src/api/cra_service.rs:263:10
         |
    263  |         .load::<TimeCountSumaryEntry>(connection)
         |          ^^^^ the trait `load_dsl::private::CompatibleType<TimeCountSumaryEntry, _>` is not implemented for `Untyped`
         |
         = help: the trait `load_dsl::private::CompatibleType<U, DB>` is implemented for `Untyped`
         = note: required because of the requirements on the impl of `LoadQuery<'_, _, TimeCountSumaryEntry>` for `SqlQuery`
    note: required by a bound in `diesel::RunQueryDsl::load

Here is the relevant code (where clauses are fixed to simplify experimentations):

#[derive(QueryableByName, Debug)]
struct TimeCountSumaryEntry {
    #[diesel(sql_type = Integer)]
    month: i32,
    #[diesel(sql_type = Integer)]
    year: i32,
    #[diesel(sql_type = Integer)]
    project_id: i32,
    #[diesel(sql_type = Text)]
    project_code: String,
    #[diesel(sql_type = Double)]
    time_spent: f32,
    #[diesel(sql_type = Text)]
    fullname: String,
}

fn _timecount_by_filters(
    user_id: Option<i32>,
    month: Option<u8>,
    year: Option<u16>,
    connection: &mut PgConnection,
) {
    let query =
        "SELECT
            EXTRACT(MONTH FROM tc.date_assigned) as \"month\",
            EXTRACT(YEAR FROM tc.date_assigned) as \"year\",
            tc.project_id as project_id,
            p.project_code as project_code,
            sum(tc.time_spent) as time_spent,
            u.lastname || ' ' || u.firstname as fullname
        FROM
            time_count tc
            JOIN cra c on tc.cra_id = c.cra_id
            JOIN project p on p.project_id = tc.project_id
            JOIN \"user\" u on u.user_id = c.user_id
        WHERE
            u.user_id = 3
            and EXTRACT(MONTH FROM tc.date_assigned) = 8
            and EXTRACT(YEAR FROM tc.date_assigned) = 2022
        GROUP BY
            tc.project_id, u.lastname, u.firstname, \"month\", \"year\", p.project_code
        ORDER BY
            \"year\", \"month\", u.lastname, u.firstname, tc.project_id";

    let time_counts_sumary = diesel::dsl::sql_query(query)
        .load::<TimeCountSumaryEntry>(connection)
        .expect("Error getting cra ids");
    println!("{:?}", time_counts_sumary);
}

I can't find any resource that mention how to deal with this use case (or even that this isn't possible at all). I first tried with the query builder, but it didn't seem possible, so I thought sql_query the way to get those data from DB (postgresql) without getting useless information in the process, but maybe there is a better one.

Does anyone have encountered this use case or have any hints about how to deal with it?

Answer 1

If someone have the same problem, I found where it was.

Diesel couldn't match types it got from sql_query and what I mentioned in TimeCountSumaryEntry .

First here:

#[diesel(sql_type = Double)]
time_spent: f32,

I mistyped the Double (it should be f64 )

And second the EXTRACT() function return a numeric in postgresql . I could use the numeric diesel feature , but in my case (year and month), an Integer is enough. So I must specify the type in the request with CAST() . Like this:

CAST(EXTRACT(MONTH FROM tc.date_assigned) as Integer) as "month",
CAST(EXTRACT(YEAR FROM tc.date_assigned) as Integer) as "year",

Here is the working code:

#[derive(QueryableByName, Debug)]
struct TimeCountSumaryEntry {
    #[diesel(sql_type = Integer)]
    month: i32,
    #[diesel(sql_type = Integer)]
    year: i32,
    #[diesel(sql_type = Integer)]
    project_id: i32,
    #[diesel(sql_type = Text)]
    project_code: String,
    #[diesel(sql_type = Double)]
    time_spent: f64,
    #[diesel(sql_type = Text)]
    fullname: String,
}

fn _timecount_by_filters(
    user_id: Option<i32>,
    month: Option<u8>,
    year: Option<u16>,
    connection: &mut PgConnection,
) {
    let query =
        "SELECT
            CAST(EXTRACT(MONTH FROM tc.date_assigned) as integer) as \"month\",
            CAST(EXTRACT(YEAR FROM tc.date_assigned) as integer) as \"year\",
            tc.project_id as project_id,
            p.project_code as project_code,
            sum(tc.time_spent) as time_spent,
            u.lastname || ' ' || u.firstname as fullname
        FROM
            time_count tc
            JOIN cra c on tc.cra_id = c.cra_id
            JOIN project p on p.project_id = tc.project_id
            JOIN \"user\" u on u.user_id = c.user_id
        WHERE
            u.user_id = 3
            and EXTRACT(MONTH FROM tc.date_assigned) = 8
            and EXTRACT(YEAR FROM tc.date_assigned) = 2022
        GROUP BY
            tc.project_id, u.lastname, u.firstname, \"month\", \"year\", p.project_code
        ORDER BY
            \"year\", \"month\", u.lastname, u.firstname, tc.project_id";

    let time_counts_sumary = diesel::dsl::sql_query(query)
        .load::<TimeCountSumaryEntry>(connection)
        .expect("Error getting cra ids");
    println!("{:?}", time_counts_sumary);
}

I found it while trying again to this query with the query builder.

I may succeed to get it work that way, I'll edit this answer when it'll be done.