This is a demonstration repository for a Diesel issue.

Setup

Versions

• Rust: 1.23.0-nightly (8b22e70b2 2017-10-31)
• Diesel: 0.16.0
• Database: postgres
• Operating System: any

Feature Flags

• diesel:
• diesel_codegen: [ "postgres" ]

Problem Description

What are you trying to accomplish?

I have a reduced test case that involves three types of DB-backed objects: Room, User and Booking. A Booking object represents a User having reserved a Room (e.g., for a meeting):

create table bookings (
	id serial primary key not null,
	room_id integer not null,
	user_id integer not null,

	foreign key (room_id) references rooms(id),
	foreign key (user_id) references users(id)
);

When I run diesel print-schema I see:

[...]
joinable!(bookings -> rooms (room_id));
joinable!(bookings -> users (user_id));

I'm also able to use a single inner_join between Booking and either Room or User:

/* ... */

#[derive(Debug, Identifiable, Queryable)]
pub struct Booking {
    pub id: i32,
    pub room_id: i32,
    pub user_id: i32,
}

type DieselResult<T> = Result<T, diesel::result::Error>;

impl Booking {
    pub fn with_rooms(c: &diesel::PgConnection) -> DieselResult<Vec<(Booking, Room)>> {
        use self::bookings::dsl::*;
        bookings.inner_join(rooms::table).load(c)
    }

    pub fn with_users(c: &diesel::PgConnection) -> DieselResult<Vec<(Booking, User)>> {
        use self::bookings::dsl::*;
        bookings.inner_join(users::table).load(c)
    }
}

Next, I want to be able to retrieve a Vec<(Booking, Room, User)> from the database by joining both bookings->rooms and bookings->users in the same query.

What is the expected output?

When I try to compile:

impl Booking {
    /* ... */
    pub fn full(c: &diesel::PgConnection) -> DieselResult<Vec<(Booking, Room, User)>> {
        use self::bookings::dsl::*;

        bookings.inner_join(rooms::table)
                .inner_join(users::table)
                .load(c)
    }
}

I would expect Diesel to generate a query like:

SELECT * from bookings
    INNER JOIN rooms ON rooms.id = room_id
    INNER JOIN users ON users.id = user_id

(i.e., joining bookings->rooms and bookings->users)

What is the actual output?

error[E0277]: the trait bound `__diesel_infer_schema::infer_rooms::rooms::table:
 diesel::JoinTo<__diesel_infer_schema::infer_users::users::table>` is not satisf
ied
  --> src/lib.rs:47:18
   |
47 |                 .inner_join(users::table)
   |                  ^^^^^^^^^^ the trait `diesel::JoinTo<__diesel_infer_schema
::infer_users::users::table>` is not implemented for `__diesel_infer_schema::inf
er_rooms::rooms::table`

So, Diesel seems to be trying to join bookings->rooms and rooms->users. I would've expected this if I were trying to compile:

bookings.inner_join(
    rooms::table.inner_join(
        users::table
    )
)

but in my use case, I'm trying to join both rooms and users with bookings individually.

Steps to reproduce

1. Create an empty database, set DATABASE_URL
2. Clone https://github.com/trombonehero/diesel-join-example
3. Execute cargo build

Checklist

• I have already looked over the issue tracker for similar issues.