Trying to write a manual FromRow implementation for a struct that contains nested structs. 9 fields limit? Is it possible?

[frederikhors]

I'm trying for the first time sqlx these days.

I'm trying to retrieve a nested struct using the below code but a srange thing is happening. If I comment-out a field in PgCoachTuple I get an error (see below).

Apparently I can have a tuple with max 9 fields. Is that right or am I doing it wrong?

Note:
As you can see I'm using a Box for pub coach: Option<Box<PgCoach>> because in other cases structs like PgCoach can have non-scalar fields (structs).

use sqlx::{postgres::PgRow, FromRow, QueryBuilder, Row};

#[derive(Debug, Default, sqlx::FromRow)]
pub struct PgCoach { //PgCoach has ONLY scalar values
    pub team_id: String,
    pub id: String,
    pub created_at: Time::OffsetDateTime,
    pub updated_at: Option<Time::OffsetDateTime>,
    pub firstname: Option<String>,
    pub lastname: Option<String>,
    pub motto: Option<String>,
    pub first_case: Option<String>,
    pub second_case: Option<String>,
    pub third_case: Option<String>,
    pub birth_date: Option<Time::OffsetDateTime>,
    pub sex: Option<i64>,
    pub phone: Option<String>,
    pub email_address: Option<String>,
    pub address: Option<String>,
    pub picture: Option<String>,
    pub notes: Option<String>,
}

type PgCoachTuple = (
    String,
    String,
    Time::OffsetDateTime,
    Option<Time::OffsetDateTime>,
    Option<String>,
    Option<String>,
    Option<String>,
    Option<String>,
    Option<String>,
    // Option<String>, // It works all good until I comment-out this field. If I do I get the below error! Crazy! Why?
    // Option<Time::OffsetDateTime>,
    // Option<i64>,
    // Option<String>,
    // Option<String>,
    // Option<String>,
    // Option<String>,
    // Option<String>,
);

#[derive(Debug, Default)]
pub struct PgPlayer {
    pub team_id: String,
    pub id: String,
    pub created_at: Time::OffsetDateTime,
    pub updated_at: Option<Time::OffsetDateTime>,
    pub score: i64,
    pub birth_date: Time::OffsetDateTime,
    pub code: String,
    pub payed: bool,
    pub coach_id: String,
    pub coach: Option<Box<PgCoach>>,
}

impl FromRow<'_, PgRow> for PgPlayer {
    fn from_row(row: &PgRow) -> sqlx::Result<Self> {
        let mut res = Self {
            team_id: row.get("team_id"),
            id: row.get("id"),
            created_at: row.get("created_at"),
            updated_at: row.get("updated_at"),
            score: row.get("score"),
            birth_date: row.get("birth_date"),
            code: row.get("code"),
            payed: row.get("payed"),
            coach_id: row.get("coach_id"),
            ..Default::default()
        };

        if row.try_get_raw("coach").is_ok() {
            res.coach = Some(Box::new(PgCoach {
                id: row.try_get::<PgCoachTuple, &str>("coach")?.1,
                firstname: row.try_get::<PgCoachTuple, &str>("coach")?.4,
                lastname: row.try_get::<PgCoachTuple, &str>("coach")?.5,
                ..Default::default()
            }));
        }

        Ok(res)
    }
}

The error is:

   Compiling project v0.1.0 (C:\projects\project\backend\src\crates\project)
error[E0277]: the trait bound `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>): sqlx::Decode<'_, Postgres>` is not satisfied
   --> src\pg.rs:539:21
    |
539 |                 id: row.try_get::<PgCoachTuple, &str>("coach")?.1,
    |                     ^^^ ------- required by a bound introduced by this call
    |                     |
    |                     the trait `sqlx::Decode<'_, Postgres>` is not implemented for `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>)`
    |
    = help: the following other types implement trait `sqlx::Decode<'r, DB>`:
              ()
              (T1, T2)
              (T1, T2, T3)
              (T1, T2, T3, T4)
              (T1, T2, T3, T4, T5)
              (T1, T2, T3, T4, T5, T6)
              (T1, T2, T3, T4, T5, T6, T7)
              (T1, T2, T3, T4, T5, T6, T7, T8)
            and 2 others
note: required by a bound in `try_get`
   --> C:\Users\Fred\.cargo\registry\src\github.com-1ecc6299db9ec823\sqlx-core-0.6.2\src\row.rs:114:12
    |
114 |         T: Decode<'r, Self::Database> + Type<Self::Database>,
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `try_get`

error[E0277]: the trait bound `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>): sqlx::Type<Postgres>` is not satisfied
   --> src\pg.rs:539:21
    |
539 |                 id: row.try_get::<PgCoachTuple, &str>("coach")?.1,
    |                     ^^^ ------- required by a bound introduced by this call
    |                     |
    |                     the trait `sqlx::Type<Postgres>` is not implemented for `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>)`
    |
    = help: the following other types implement trait `sqlx::Type<DB>`:
              ()
              (T1, T2)
              (T1, T2, T3)
              (T1, T2, T3, T4)
              (T1, T2, T3, T4, T5)
              (T1, T2, T3, T4, T5, T6)
              (T1, T2, T3, T4, T5, T6, T7)
              (T1, T2, T3, T4, T5, T6, T7, T8)
            and 2 others
note: required by a bound in `try_get`
   --> C:\Users\Fred\.cargo\registry\src\github.com-1ecc6299db9ec823\sqlx-core-0.6.2\src\row.rs:114:41
    |
114 |         T: Decode<'r, Self::Database> + Type<Self::Database>,
    |                                         ^^^^^^^^^^^^^^^^^^^^ required by this bound in `try_get`

error[E0277]: the trait bound `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>): sqlx::Decode<'_, Postgres>` is not satisfied
   --> src\pg.rs:540:28
    |
540 |                 firstname: row.try_get::<PgCoachTuple, &str>("coach")?.4,
    |                            ^^^ ------- required by a bound introduced by this call
    |                            |
    |                            the trait `sqlx::Decode<'_, Postgres>` is not implemented for `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>)`
    |
    = help: the following other types implement trait `sqlx::Decode<'r, DB>`:
              ()
              (T1, T2)
              (T1, T2, T3)
              (T1, T2, T3, T4)
              (T1, T2, T3, T4, T5)
              (T1, T2, T3, T4, T5, T6)
              (T1, T2, T3, T4, T5, T6, T7)
              (T1, T2, T3, T4, T5, T6, T7, T8)
            and 2 others
note: required by a bound in `try_get`
   --> C:\Users\Fred\.cargo\registry\src\github.com-1ecc6299db9ec823\sqlx-core-0.6.2\src\row.rs:114:12
    |
114 |         T: Decode<'r, Self::Database> + Type<Self::Database>,
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `try_get`

error[E0277]: the trait bound `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>): sqlx::Type<Postgres>` is not satisfied
   --> src\pg.rs:540:28
    |
540 |                 firstname: row.try_get::<PgCoachTuple, &str>("coach")?.4,
    |                            ^^^ ------- required by a bound introduced by this call
    |                            |
    |                            the trait `sqlx::Type<Postgres>` is not implemented for `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>)`
    |
    = help: the following other types implement trait `sqlx::Type<DB>`:
              ()
              (T1, T2)
              (T1, T2, T3)
              (T1, T2, T3, T4)
              (T1, T2, T3, T4, T5)
              (T1, T2, T3, T4, T5, T6)
              (T1, T2, T3, T4, T5, T6, T7)
              (T1, T2, T3, T4, T5, T6, T7, T8)
            and 2 others
note: required by a bound in `try_get`
   --> C:\Users\Fred\.cargo\registry\src\github.com-1ecc6299db9ec823\sqlx-core-0.6.2\src\row.rs:114:41
    |
114 |         T: Decode<'r, Self::Database> + Type<Self::Database>,
    |                                         ^^^^^^^^^^^^^^^^^^^^ required by this bound in `try_get`

error[E0277]: the trait bound `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>): sqlx::Decode<'_, Postgres>` is not satisfied
   --> src\pg.rs:541:27
    |
541 |                 lastname: row.try_get::<PgCoachTuple, &str>("coach")?.5,
    |                           ^^^ ------- required by a bound introduced by this call
    |                           |
    |                           the trait `sqlx::Decode<'_, Postgres>` is not implemented for `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>)`
    |
    = help: the following other types implement trait `sqlx::Decode<'r, DB>`:
              ()
              (T1, T2)
              (T1, T2, T3)
              (T1, T2, T3, T4)
              (T1, T2, T3, T4, T5)
              (T1, T2, T3, T4, T5, T6)
              (T1, T2, T3, T4, T5, T6, T7)
              (T1, T2, T3, T4, T5, T6, T7, T8)
            and 2 others
note: required by a bound in `try_get`
   --> C:\Users\Fred\.cargo\registry\src\github.com-1ecc6299db9ec823\sqlx-core-0.6.2\src\row.rs:114:12
    |
114 |         T: Decode<'r, Self::Database> + Type<Self::Database>,
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `try_get`

error[E0277]: the trait bound `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>): sqlx::Type<Postgres>` is not satisfied
   --> src\pg.rs:541:27
    |
541 |                 lastname: row.try_get::<PgCoachTuple, &str>("coach")?.5,
    |                           ^^^ ------- required by a bound introduced by this call
    |                           |
    |                           the trait `sqlx::Type<Postgres>` is not implemented for `(std::string::String, std::string::String, time::OffsetDateTime, Option<time::OffsetDateTime>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>, Option<std::string::String>)`
    |
    = help: the following other types implement trait `sqlx::Type<DB>`:
              ()
              (T1, T2)
              (T1, T2, T3)
              (T1, T2, T3, T4)
              (T1, T2, T3, T4, T5)
              (T1, T2, T3, T4, T5, T6)
              (T1, T2, T3, T4, T5, T6, T7)
              (T1, T2, T3, T4, T5, T6, T7, T8)
            and 2 others
note: required by a bound in `try_get`
   --> C:\Users\Fred\.cargo\registry\src\github.com-1ecc6299db9ec823\sqlx-core-0.6.2\src\row.rs:114:41
    |
114 |         T: Decode<'r, Self::Database> + Type<Self::Database>,
    |                                         ^^^^^^^^^^^^^^^^^^^^ required by this bound in `try_get`

For more information about this error, try `rustc --explain E0277`.

What does all this mean?

Is there another simpler way to do the same?

[frederikhors]

@abonander an hint would help a lot. I can help with docs PRs if I get to it.

[frederikhors]

The answer is they support only 9 field tuples. This is really bad. :(

https://stackoverflow.com/questions/75084479/trying-to-write-a-manual-fromrow-implementation-for-a-struct-that-contains-nes