@weiznich I appreciate your help earlier, in case you're curious I figured out the issue: It turns out it had nothing to do with diesel or my ToSql impl; Postgres' implementation of IS NOT NULL on composite types is a very strange design decision: https://stackoverflow.com/questions/22763151/check-if-a-postgres-composite-field-is-null-empty

I had a check constraint on (VALUE).inner_thing IS NOT NULL, so it was checking every field of the type. I changed the constraint to ((VALUE).inner_thing)::text IS NOT NULL, it seems to work.

Hi there, been searching/implementing solutions for this error for a struct with UUID as ID and is Insertable, but can’t seem to trace the problem, was hoping someone could chime in.

Feature flags seem Ok but I suspect this may be the issue.

Error:

error[E0277]: the trait bound `uuid::Uuid: diesel::Expression` is not satisfied
  --> src/protocol/model.rs:37:40
   |
37 | #[cfg_attr(feature = "backend", derive(Insertable, Queryable))]
   |                                        ^^^^^^^^^^ the trait `diesel::Expression` is not implemented for `uuid::Uuid`
   |
   = note: required because of the requirements on the impl of `diesel::Expression` for `&uuid::Uuid`
   = note: required because of the requirements on the impl of `diesel::expression::AsExpression<diesel::sql_types::Uuid>` for `&uuid::Uuid`

Cargo.toml

[dependencies]
diesel = { version = "1.4.2", optional = true, features = ["postgres", "uuid", "r2d2", "chrono"]}
chrono = { version = "0.4.9", optional=true, features = ["serde"]}
uuid = {version="0.7.4", optional=true, features=["serde", "v4"]}

[features]
backend = ["diesel", "uuid", "chrono"]
[workspace]
members = [
    "backend",
]

Struct:

#[cfg_attr(feature = "backend", derive(Insertable, Queryable))]
#[cfg_attr(feature = "backend", table_name = "invitations")]
#[derive(Debug, PartialEq, Deserialize, Serialize)]
pub struct Invitation {
    #[cfg(feature = "backend")]
    pub id: uuid::Uuid,
    pub email: String,
    #[cfg(feature = "backend")]
    pub expires_at: chrono::NaiveDateTime,
}

Any ideas? Thanks in advance, you guys are awesome.

#[macro_use]
extern crate diesel;

use diesel::prelude::*;
use schema::posts::dsl::*;

mod schema {
    table! {
        posts (id) {
            id -> Int4,
        }
    }
}

fn main() {
    let connection = PgConnection::establish("fake example only").unwrap();
    let _id: i32 = diesel::insert_into(posts)
        .values(id.eq(1))
        .returning(id)
        .execute(&connection)
        .unwrap();
}

error[E0308]: mismatched types
  --> src/main.rs:17:20
   |
17 |       let _id: i32 = diesel::insert_into(posts)
   |  ____________________^
18 | |         .values(id.eq(1))
19 | |         .returning(id)
20 | |         .execute(&connection)
21 | |         .unwrap();
   | |_________________^ expected i32, found usize
help: you can convert an `usize` to `i32` and panic if the converted value wouldn't fit
   |
17 |     let _id: i32 = diesel::insert_into(posts)
18 |         .values(id.eq(1))
19 |         .returning(id)
20 |         .execute(&connection)
21 |         .unwrap().try_into().unwrap();
   |