An async interface for diesel

Diesel gets rid of the boilerplate for database interaction and eliminates runtime errors without sacrificing performance. It takes full advantage of Rust's type system to create a low overhead query builder that "feels like Rust."

Diesel-async provides an async implementation of diesels connection implementation and any method that may issue an query. It is designed as pure async drop-in replacement for the corresponding diesel methods. Similar to diesel the crate is designed in a way that allows third party crates to extend the existing infrastructure and even provide their own connection implementations.

Supported databases:

1. PostgreSQL
2. MySQL

Usage

Simple usage

Diesel-async is designed to work in combination with diesel, not to replace diesel. For this it provides drop-in replacement for diesel functionality that actually interacts with the database.

A normal project should use a setup similar to the following one:

[dependencies]
diesel = "2.1.0" # no backend features need to be enabled
diesel-async = { version = "0.3.1", features = ["postgres"] }

This allows to import the relevant traits from both crates:

use diesel::prelude::*;
use diesel_async::{RunQueryDsl, AsyncConnection, AsyncPgConnection};

// ordinary diesel model setup

table! {
    users {
        id -> Integer,
        name -> Text,
    }
}

#[derive(Queryable, Selectable)]
#[diesel(table_name = users)]
struct User {
    id: i32,
    name: String,
}

// create an async connection
let mut connection = AsyncPgConnection::establish(&std::env::var("DATABASE_URL")?).await?;

// use ordinary diesel query dsl to construct your query
let data: Vec<User> = users::table
    .filter(users::id.gt(0))
    .or_filter(users::name.like("%Luke"))
    .select(User::as_select())
    // execute the query via the provided
    // async `diesel_async::RunQueryDsl`
    .load(&mut connection)
    .await?;

Async Transaction Support

Diesel-async provides an ergonomic interface to wrap several statements into a shared database transaction. Such transactions are automatically rolled back as soon as the inner closure returns an error

connection.transaction::<_, diesel::result::Error, _>(|conn| async move {
         diesel::insert_into(users::table)
             .values(users::name.eq("Ruby"))
             .execute(conn)
             .await?;

         let all_names = users::table.select(users::name).load::<String>(conn).await?;
         Ok(())
       }.scope_boxed()
    ).await?;

Streaming Query Support

Beside loading data directly into a vector, diesel-async also supports returning a value stream for each query. This allows to process data from the database while they are still received.

// use ordinary diesel query dsl to construct your query
let data: impl Stream<Item = QueryResult<User>> = users::table
    .filter(users::id.gt(0))
    .or_filter(users::name.like("%Luke"))
    .select(User::as_select())
    // execute the query via the provided
    // async `diesel_async::RunQueryDsl`
    .load_stream(&mut connection)
    .await?;

Built-in Connection Pooling Support

Diesel-async provides built-in support for several connection pooling crates. This includes support for:

• deadpool
• bb8
• mobc

Deadpool

use diesel_async::pooled_connection::AsyncDieselConnectionManager;
use diesel_async::pooled_connection::deadpool::Pool;
use diesel_async::RunQueryDsl;

// create a new connection pool with the default config
let config = AsyncDieselConnectionManager::<diesel_async::AsyncPgConnection>::new(std::env::var("DATABASE_URL")?);
let pool = Pool::builder(config).build()?;

// checkout a connection from the pool
let mut conn = pool.get().await?;

// use the connection as ordinary diesel-async connection
let res = users::table.select(User::as_select()).load::(&mut conn).await?;

BB8

use diesel_async::pooled_connection::AsyncDieselConnectionManager;
use diesel_async::pooled_connection::bb8::Pool;
use diesel_async::RunQueryDsl;

// create a new connection pool with the default config
let config = AsyncDieselConnectionManager::<diesel_async::AsyncPgConnection>::new(std::env::var("DATABASE_URL")?);
let pool = Pool::builder().build(config).await?;

// checkout a connection from the pool
let mut conn = pool.get().await?;

// use the connection as ordinary diesel-async connection
let res = users::table.select(User::as_select()).load::(&mut conn).await?;

Mobc

use diesel_async::pooled_connection::AsyncDieselConnectionManager;
use diesel_async::pooled_connection::mobc::Pool;
use diesel_async::RunQueryDsl;

// create a new connection pool with the default config
let config = AsyncDieselConnectionManager::<diesel_async::AsyncPgConnection>::new(std::env::var("DATABASE_URL")?);
let pool = Pool::new(config);

// checkout a connection from the pool
let mut conn = pool.get().await?;

// use the connection as ordinary diesel-async connection
let res = users::table.select(User::as_select()).load::(&mut conn).await?;

Diesel-Async with Secure Database

In the event of using this crate with a sslmode=require flag, it will be necessary to build a TLS cert. There is an example provided for doing this using the rustls crate in the postgres examples folder.

Crate Feature Flags

Diesel-async offers several configurable features:

• postgres: Enables the implementation of AsyncPgConnection
• mysql: Enables the implementation of AsyncMysqlConnection
• deadpool: Enables support for the deadpool connection pool implementation
• bb8: Enables support for the bb8 connection pool implementation
• mobc: Enables support for the mobc connection pool implementation

By default no features are enabled.

Code of conduct

Anyone who interacts with Diesel in any space, including but not limited to this GitHub repository, must follow our code of conduct.

License

Licensed under either of these:

• Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

Contributing

Contributions are explicitly welcome. Please consider opening a discussion with your idea first, to discuss possible designs.

Unless you explicitly state otherwise, any contribution you intentionally submit for inclusion in the work, as defined in the Apache-2.0 license, shall be dual-licensed as above, without any additional terms or conditions.