Boxed Queries are not thread safe.

[seunlanlege]

Setup

Versions

• Rust: rustc 1.26.0-nightly (ae544ee1c 2018-03-29)
• Diesel: { version = "1.1.0" }
• Database: postgres
• Operating System

Feature Flags

• diesel: ["postgres"]

Problem Description

disel

	let query = payments::table.filter(payments::company_id.eq(companyId)).into_boxed(); // adding `.into_boxed()` causes `query` to no longer be thread safe
	let future = async::query(move |conn| query.get_result::<models::Payment>(conn));

async::query will spawn the closure on a futures cpupool and requires that the closure contain thread safe items.

What are you trying to accomplish?

What is the expected output?

What is the actual output?

error[E0277]: the trait bound `diesel::query_builder::QueryFragment<diesel::pg::Pg>: std::marker::Send` is not satisfied
  --> src/services/paymenthistory/paymenthistory.rs:23:15
   |
23 |     let future = async::query(move |conn| query.get_result::<models::Payment>(conn));
   |                  ^^^^^^^^^^^^ `diesel::query_builder::QueryFragment<diesel::pg::Pg>` cannot be sent between threads safely
   |
   = help: the trait `std::marker::Send` is not implemented for `diesel::query_builder::QueryFragment<diesel::pg::Pg>`
   = note: required because of the requirements on the impl of `std::marker::Send` for `std::ptr::Unique<diesel::query_builder::QueryFragment<diesel::pg::Pg>>`
   = note: required because it appears within the type `std::boxed::Box<diesel::query_builder::QueryFragment<diesel::pg::Pg>>`
   = note: required because it appears within the type `diesel::query_builder::BoxedSelectStatement<'_, (diesel::sql_types::BigInt, diesel::sql_types::BigInt, diesel::sql_types::BigInt, diesel::sql_types::BigInt, diesel::sql_types::BigInt, db::schema::db_enum_impl_Status::StatusMapping, diesel::sql_types::Text, diesel::sql_types::Text), db::schema::payments::table, diesel::pg::Pg>`
   = note: required because it appears within the type `[closure@src/services/paymenthistory/paymenthistory.rs:23:28: 23:81 query:diesel::query_builder::BoxedSelectStatement<'_, (diesel::sql_types::BigInt, diesel::sql_types::BigInt, diesel::sql_types::BigInt, diesel::sql_types::BigInt, diesel::sql_types::BigInt, db::schema::db_enum_impl_Status::StatusMapping, diesel::sql_types::Text, diesel::sql_types::Text), db::schema::payments::table, diesel::pg::Pg>]`
note: required by `db::async::query`
  --> src/db/async.rs:24:1
   |
24 | / pub fn query<T, F, R>(f: F) -> impl Future<Item = T, Error = result::Error>
25 | | where
26 | |     T: Send + 'static,
27 | |     F: FnOnce(&Conn) -> R + Send + 'static,
...  |
49 | |     })
50 | | }
   | |_^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
error: Could not compile `paysquare`.

To learn more, run the command again with --verbose.

Are you seeing any additional errors?

Steps to reproduce

Checklist

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

[sgrif]

Thank you for the report. However, making boxed queries Send would require a major breaking change, and isn't likely to happen right now. I suggest waiting until the query has been moved into your closure to box it, or just constructing the query entirely on that thread.