Why did we make Diesel?

Preventing Runtime Errors

We don’t want to waste time tracking down runtime errors. We achieve this by having Diesel eliminate the possibility of incorrect database interactions at compile time.

Built for Performance

Diesel offers a high level query builder and lets you think about your problems in Rust, not SQL. Our focus on zero-cost abstractions allows Diesel to run your query and load your data even faster than C.

Productive and Extensible

Unlike Active Record and other ORMs, Diesel is designed to be abstracted over. Diesel enables you to write reusable code and think in terms of your problem domain and not SQL.

See some examples

Simple queries are a complete breeze. Loading all users from a database:

Rust code
users::table.load(&mut connection)
Executed SQL
SELECT * FROM users;

Loading all the posts for a user:

Rust code
Post::belonging_to(user).load(&mut connection)
Executed SQL
SELECT * FROM posts WHERE user_id = 1;

Diesel’s powerful query builder helps you construct queries as simple or complex as you need, at zero cost.

Rust code
let versions = Version::belonging_to(krate)
  .select(id)
  .order(num.desc())
  .limit(5);
let downloads = version_downloads
  .filter(date.gt(now - 90.days()))
  .filter(version_id.eq(any(versions)))
  .order(date)
  .load::<Download>(&mut conn)?;
Executed SQL
SELECT version_downloads.*
  WHERE date > (NOW() - '90 days')
    AND version_id = ANY(
      SELECT id FROM versions
        WHERE crate_id = 1
        ORDER BY num DESC
        LIMIT 5
    )
  ORDER BY date

Diesel codegen generates boilerplate for you. It lets you focus on your business logic, not mapping to and from SQL rows.

That means you can write this:

With Diesel
#[derive(Queryable)]
pub struct Download {
    id: i32,
    version_id: i32,
    downloads: i32,
    counted: i32,
    date: SystemTime,
}

Instead of this:

Without Diesel
pub struct Download {
    id: i32,
    version_id: i32,
    downloads: i32,
    counted: i32,
    date: SystemTime,
}

impl Download {
    fn from_row(row: &Row) -> Download {
        Download {
            id: row.get("id"),
            version_id: row.get("version_id"),
            downloads: row.get("downloads"),
            counted: row.get("counted"),
            date: row.get("date"),
        }
    }
}

It’s not just about reading data. Diesel makes it easy to use structs for new records.

Rust code
#[derive(Insertable)]
#[table_name="users"]
struct NewUser<'a> {
    name: &'a str,
    hair_color: Option<&'a str>,
}

let new_users = vec![
    NewUser { name: "Sean", hair_color: Some("Black") },
    NewUser { name: "Gordon", hair_color: None },
];

insert_into(users)
    .values(&new_users)
    .execute(&mut connection);
Executed SQL
INSERT INTO users (name, hair_color) VALUES
  ('Sean', 'Black'),
  ('Gordon', DEFAULT)

If you need data from the rows you inserted, just change execute to get_result or get_results. Diesel will take care of the rest.

Rust code
let new_users = vec![
    NewUser { name: "Sean", hair_color: Some("Black") },
    NewUser { name: "Gordon", hair_color: None },
];

let inserted_users = insert_into(users)
    .values(&new_users)
    .get_results::<User>(&mut connection);
Executed SQL
INSERT INTO users (name, hair_color) VALUES
  ('Sean', 'Black'),
  ('Gordon', DEFAULT)
  RETURNING *

Diesel’s codegen can generate several ways to update a row, letting you encapsulate your logic in the way that makes sense for your app.

Modifying a struct
post.published = true;
post.save_changes(&mut connection);
One-off batch changes
update(users.filter(email.like("%@spammer.com")))
    .set(banned.eq(true))
    .execute(&mut connection)
Using a struct for encapsulation
update(Settings::belonging_to(current_user))
    .set(&settings_form)
    .execute(&mut connection)

There will always be certain queries that are just easier to write as raw SQL, or can’t be expressed with the query builder. Even in these cases, Diesel provides an easy to use API for writing raw SQL.

Running raw SQL
#[derive(QueryableByName)]
#[table_name = "users"]
struct User {
    id: i32,
    name: String,
    organization_id: i32,
}

// Using `include_str!` allows us to keep the SQL in a
// separate file, where our editor can give us SQL specific
// syntax highlighting.
sql_query(include_str!("complex_users_by_organization.sql"))
    .bind::<Integer, _>(organization_id)
    .bind::<BigInt, _>(offset)
    .bind::<BigInt, _>(limit)
    .load::<User>(&mut conn)?;

The community has made some utilities to help make diesel even easier to work with!

dsync License: MIT OR Apache-2.0

Generate rust structs & query functions from diesel schema files.

diesel-logger License: MIT OR Apache-2.0

A generic diesel connection implementations that allows to log any executed query.

diesel-oci License: MIT OR Apache-2.0

A diesel backend and connection implementation for oracles database system.

rsfbclient-diesel License: MIT

A diesel backend and connection implementation for the Firebird database system.

diesel-async License: AGPL3+

An experimental async diesel connection implementation for PostgreSQL and MySQL.

Something missing? Submit an issue here.