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

users::table.load(&mut connection)

SELECT * FROM users;

Loading all the posts for a user:

Post::belonging_to(user).load(&mut connection)

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.

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)?;

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:

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

Instead of this:

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.

#[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);

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.

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);

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.

post.published = true;
post.save_changes(&mut connection);

update(users.filter(email.like("%@spammer.com")))
    .set(banned.eq(true))
    .execute(&mut connection)

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.

#[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!

Something missing? Submit an issue here.