Trait diesel::prelude::QueryDsl

pub trait QueryDsl: Sized {
    // Provided methods
    fn distinct(self) -> Distinct<Self>
       where Self: DistinctDsl { ... }
    fn select<Selection>(self, selection: Selection) -> Select<Self, Selection>
       where Selection: Expression,
             Self: SelectDsl<Selection> { ... }
    fn count(self) -> Select<Self, CountStar>
       where Self: SelectDsl<CountStar> { ... }
    fn inner_join<Rhs>(self, rhs: Rhs) -> InnerJoin<Self, Rhs>
       where Self: JoinWithImplicitOnClause<Rhs, Inner> { ... }
    fn left_outer_join<Rhs>(self, rhs: Rhs) -> LeftJoin<Self, Rhs>
       where Self: JoinWithImplicitOnClause<Rhs, LeftOuter> { ... }
    fn left_join<Rhs>(self, rhs: Rhs) -> LeftJoin<Self, Rhs>
       where Self: JoinWithImplicitOnClause<Rhs, LeftOuter> { ... }
    fn filter<Predicate>(self, predicate: Predicate) -> Filter<Self, Predicate>
       where Self: FilterDsl<Predicate> { ... }
    fn or_filter<Predicate>(
        self,
        predicate: Predicate,
    ) -> OrFilter<Self, Predicate>
       where Self: OrFilterDsl<Predicate> { ... }
    fn find<PK>(self, id: PK) -> Find<Self, PK>
       where Self: FindDsl<PK> { ... }
    fn order<Expr>(self, expr: Expr) -> Order<Self, Expr>
       where Expr: Expression,
             Self: OrderDsl<Expr> { ... }
    fn order_by<Expr>(self, expr: Expr) -> OrderBy<Self, Expr>
       where Expr: Expression,
             Self: OrderDsl<Expr> { ... }
    fn then_order_by<Order>(self, order: Order) -> ThenOrderBy<Self, Order>
       where Self: ThenOrderDsl<Order> { ... }
    fn limit(self, limit: i64) -> Limit<Self>
       where Self: LimitDsl { ... }
    fn offset(self, offset: i64) -> Offset<Self>
       where Self: OffsetDsl { ... }
    fn group_by<GB>(self, group_by: GB) -> GroupBy<Self, GB>
       where GB: Expression,
             Self: GroupByDsl<GB> { ... }
    fn having<Predicate>(self, predicate: Predicate) -> Having<Self, Predicate>
       where Self: HavingDsl<Predicate> { ... }
    fn for_update(self) -> ForUpdate<Self>
       where Self: LockingDsl<ForUpdate> { ... }
    fn for_no_key_update(self) -> ForNoKeyUpdate<Self>
       where Self: LockingDsl<ForNoKeyUpdate> { ... }
    fn for_share(self) -> ForShare<Self>
       where Self: LockingDsl<ForShare> { ... }
    fn for_key_share(self) -> ForKeyShare<Self>
       where Self: LockingDsl<ForKeyShare> { ... }
    fn skip_locked(self) -> SkipLocked<Self>
       where Self: ModifyLockDsl<SkipLocked> { ... }
    fn no_wait(self) -> NoWait<Self>
       where Self: ModifyLockDsl<NoWait> { ... }
    fn into_boxed<'a, DB>(self) -> IntoBoxed<'a, Self, DB>
       where DB: Backend,
             Self: BoxedDsl<'a, DB> { ... }
    fn single_value(self) -> SingleValue<Self>
       where Self: SingleValueDsl { ... }
    fn nullable(self) -> NullableSelect<Self>
       where Self: SelectNullableDsl { ... }
}

Methods used to construct select statements.

Provided Methods

fn distinct(self) -> Distinct<Self>

where Self: DistinctDsl,

Adds the DISTINCT keyword to a query.

This method will override any previous distinct clause that was present. For example, on PostgreSQL, foo.distinct_on(bar).distinct() will create the same query as foo.distinct().

Example

diesel::insert_into(users)
    .values(&vec![name.eq("Sean"); 3])
    .execute(connection)?;
let names = users.select(name).load::<String>(connection)?;
let distinct_names = users.select(name).distinct().load::<String>(connection)?;

assert_eq!(vec!["Sean"; 3], names);
assert_eq!(vec!["Sean"; 1], distinct_names);

fn select<Selection>(self, selection: Selection) -> Select<Self, Selection>

where Selection: Expression, Self: SelectDsl<Selection>,

Adds a SELECT clause to the query.

If there was already a select clause present, it will be overridden. For example, foo.select(bar).select(baz) will produce the same query as foo.select(baz).

By default, the select clause will be roughly equivalent to SELECT * (however, Diesel will list all columns to ensure that they are in the order we expect).

select has slightly stricter bounds on its arguments than other methods. In particular, when used with a left outer join, .nullable must be called on columns that come from the right side of a join. It can be called on the column itself, or on an expression containing that column. title.nullable(), lower(title).nullable(), and (id, title).nullable() would all be valid.

In order to use this method with columns from different tables a method like .inner_join or .left_join needs to be called before calling .select (See examples below). This is because you can only access columns from tables that appear in your query before that function call.

Examples

// By default, all columns will be selected
let all_users = users.load::<(i32, String)>(connection)?;
assert_eq!(vec![(1, String::from("Sean")), (2, String::from("Tess"))], all_users);

let all_names = users.select(name).load::<String>(connection)?;
assert_eq!(vec!["Sean", "Tess"], all_names);

When used with a left join

let join = users::table.left_join(posts::table);

// By default, all columns from both tables are selected.
// If no explicit select clause is used this means that the result
// type of this query must contain all fields from the original schema in order.
let all_data = join.load::<(User, Option<Post>)>(connection)?;
let expected_data = vec![
    (User::new(1, "Sean"), Some(Post::new(post_id, 1, "Sean's Post"))),
    (User::new(2, "Tess"), None),
];
assert_eq!(expected_data, all_data);

// Since `posts` is on the right side of a left join, `.nullable` is
// needed.
let names_and_titles = join.select((users::name, posts::title.nullable()))
    .load::<(String, Option<String>)>(connection)?;
let expected_data = vec![
    (String::from("Sean"), Some(String::from("Sean's Post"))),
    (String::from("Tess"), None),
];
assert_eq!(expected_data, names_and_titles);

fn count(self) -> Select<Self, CountStar>

where Self: SelectDsl<CountStar>,

Get the count of a query. This is equivalent to .select(count_star())

Example

let count = users.count().get_result(connection);
assert_eq!(Ok(2), count);

fn inner_join<Rhs>(self, rhs: Rhs) -> InnerJoin<Self, Rhs>

where Self: JoinWithImplicitOnClause<Rhs, Inner>,

Join two tables using a SQL INNER JOIN.

If you have invoked joinable! for the two tables, you can pass that table directly. Otherwise you will need to use .on to specify the ON clause.

You can join to as many tables as you’d like in a query, with the restriction that no table can appear in the query more than once. For tables that appear more than once in a single query the usage of alias! is required.

You will also need to call allow_tables_to_appear_in_same_query!. If you are using diesel print-schema, this will have been generated for you. See the documentation for allow_tables_to_appear_in_same_query! for details.

Diesel expects multi-table joins to be semantically grouped based on the relationships. For example, users.inner_join(posts.inner_join(comments)) is not the same as users.inner_join(posts).inner_join(comments). The first would deserialize into (User, (Post, Comment)) and generate the following SQL:

SELECT * FROM users
    INNER JOIN (
        posts
        INNER JOIN comments ON comments.post_id = posts.id
    ) ON posts.user_id = users.id

While the second query would deserialize into (User, Post, Comment) and generate the following SQL:

SELECT * FROM users
    INNER JOIN posts ON posts.user_id = users.id
    INNER JOIN comments ON comments.user_id = users.id

The exact generated SQL may change in future diesel version as long as the generated query continues to produce same results. The currently generated SQL is referred as “explicit join” by the PostgreSQL documentation and may have implications on the chosen query plan for large numbers of joins in the same query. Checkout the documentation of the join_collapse_limit parameter to control this behaviour.

Note that in order to use this method with .select, you will need to use it before calling .select (See examples below). This is because you can only access columns from tables that appear in your query before the call to .select.

Examples

With implicit ON clause

joinable!(posts -> users (user_id));
allow_tables_to_appear_in_same_query!(users, posts);

let data = users.inner_join(posts)
    .select((name, title))
    .load(connection);

let expected_data = vec![
    (String::from("Sean"), String::from("My first post")),
    (String::from("Sean"), String::from("About Rust")),
    (String::from("Tess"), String::from("My first post too")),
];
assert_eq!(Ok(expected_data), data);

With explicit ON clause

allow_tables_to_appear_in_same_query!(users, posts);

diesel::insert_into(posts)
    .values(&vec![
        (user_id.eq(1), title.eq("Sean's post")),
        (user_id.eq(2), title.eq("Sean is a jerk")),
    ])
    .execute(connection)
    .unwrap();

let data = users
    .inner_join(posts.on(title.like(name.concat("%"))))
    .select((name, title))
    .load(connection);
let expected_data = vec![
    (String::from("Sean"), String::from("Sean's post")),
    (String::from("Sean"), String::from("Sean is a jerk")),
];
assert_eq!(Ok(expected_data), data);

With explicit ON clause (struct)

allow_tables_to_appear_in_same_query!(users, posts);

#[derive(Debug, PartialEq, Queryable)]
struct User {
    id: i32,
    name: String,
}

#[derive(Debug, PartialEq, Queryable)]
struct Post {
    id: i32,
    user_id: i32,
    title: String,
}

diesel::insert_into(posts)
    .values(&vec![
        (user_id.eq(1), title.eq("Sean's post")),
        (user_id.eq(2), title.eq("Sean is a jerk")),
    ])
    .execute(connection)
    .unwrap();

// By default, all columns from both tables are selected.
// If no explicit select clause is used this means that the
// result type of this query must contain all fields from the
// original schema in order.
let data = users
    .inner_join(posts.on(title.like(name.concat("%"))))
    .load::<(User, Post)>(connection); // type could be elided
let expected_data = vec![
    (
        User { id: 1, name: String::from("Sean") },
        Post { id: 4, user_id: 1, title: String::from("Sean's post") },
    ),
    (
        User { id: 1, name: String::from("Sean") },
        Post { id: 5, user_id: 2, title: String::from("Sean is a jerk") },
    ),
];
assert_eq!(Ok(expected_data), data);

fn left_outer_join<Rhs>(self, rhs: Rhs) -> LeftJoin<Self, Rhs>

where Self: JoinWithImplicitOnClause<Rhs, LeftOuter>,

Join two tables using a SQL LEFT OUTER JOIN.

Behaves similarly to inner_join, but will produce a left join instead. See inner_join for usage examples.

Columns in the right hand table will become Nullable which means you must call nullable() on the corresponding fields in the select clause:

Selecting after a left join

let join = users::table.left_join(posts::table);

// Since `posts` is on the right side of a left join, `.nullable` is
// needed.
let names_and_titles = join.select((users::name, posts::title.nullable()))
    .load::<(String, Option<String>)>(connection)?;
let expected_data = vec![
    (String::from("Sean"), Some(String::from("Sean's Post"))),
    (String::from("Tess"), None),
];
assert_eq!(expected_data, names_and_titles);

fn left_join<Rhs>(self, rhs: Rhs) -> LeftJoin<Self, Rhs>

where Self: JoinWithImplicitOnClause<Rhs, LeftOuter>,

Alias for left_outer_join.

fn filter<Predicate>(self, predicate: Predicate) -> Filter<Self, Predicate>

where Self: FilterDsl<Predicate>,

Adds to the WHERE clause of a query.

If there is already a WHERE clause, the result will be old AND new.

Note that in order to use this method with columns from different tables, you need to call .inner_join or .left_join beforehand. This is because you can only access columns from tables that appear in your query before the call to .filter.

Example:

let seans_id = users.filter(name.eq("Sean")).select(id)
    .first(connection);
assert_eq!(Ok(1), seans_id);
let tess_id = users.filter(name.eq("Tess")).select(id)
    .first(connection);
assert_eq!(Ok(2), tess_id);

fn or_filter<Predicate>(self, predicate: Predicate) -> OrFilter<Self, Predicate>

where Self: OrFilterDsl<Predicate>,

Adds to the WHERE clause of a query using OR

If there is already a WHERE clause, the result will be (old OR new). Calling foo.filter(bar).or_filter(baz) is identical to foo.filter(bar.or(baz)). However, the second form is much harder to do dynamically.

Example:

diesel::insert_into(animals)
    .values(&vec![
        (species.eq("cat"), legs.eq(4), name.eq("Sinatra")),
        (species.eq("dog"), legs.eq(3), name.eq("Fido")),
        (species.eq("spider"), legs.eq(8), name.eq("Charlotte")),
    ])
    .execute(connection)?;

let good_animals = animals
    .filter(name.eq("Fido"))
    .or_filter(legs.eq(4))
    .select(name)
    .get_results::<Option<String>>(connection)?;
let expected = vec![
    Some(String::from("Sinatra")),
    Some(String::from("Fido")),
];
assert_eq!(expected, good_animals);

fn find<PK>(self, id: PK) -> Find<Self, PK>

where Self: FindDsl<PK>,

Attempts to find a single record from the given table by primary key.

Example

let sean = (1, "Sean".to_string());
let tess = (2, "Tess".to_string());
assert_eq!(Ok(sean), users.find(1).first(connection));
assert_eq!(Ok(tess), users.find(2).first(connection));
assert_eq!(Err::<(i32, String), _>(NotFound), users.find(3).first(connection));

fn order<Expr>(self, expr: Expr) -> Order<Self, Expr>

where Expr: Expression, Self: OrderDsl<Expr>,

Sets the order clause of a query.

If there was already an order clause, it will be overridden. See also: .desc() and .asc()

Ordering by multiple columns can be achieved by passing a tuple of those columns. To construct an order clause of an unknown number of columns, see QueryDsl::then_order_by

Examples

diesel::insert_into(users)
    .values(&vec![
        name.eq("Saul"),
        name.eq("Steve"),
        name.eq("Stan"),
    ])
    .execute(connection)?;

let ordered_names = users.select(name)
    .order(name.desc())
    .load::<String>(connection)?;
assert_eq!(vec!["Steve", "Stan", "Saul"], ordered_names);

diesel::insert_into(users).values(name.eq("Stan")).execute(connection)?;

let data = users.select((name, id))
    .order((name.asc(), id.desc()))
    .load(connection)?;
let expected_data = vec![
    (String::from("Saul"), 3),
    (String::from("Stan"), 6),
    (String::from("Stan"), 5),
    (String::from("Steve"), 4),
];
assert_eq!(expected_data, data);

fn order_by<Expr>(self, expr: Expr) -> OrderBy<Self, Expr>

where Expr: Expression, Self: OrderDsl<Expr>,

Alias for order

fn then_order_by<Order>(self, order: Order) -> ThenOrderBy<Self, Order>

where Self: ThenOrderDsl<Order>,

Appends to the ORDER BY clause of this SQL query.

Unlike .order, this method will append rather than replace. In other words, .order_by(foo).order_by(bar) is equivalent to .order_by(bar). In contrast, .order_by(foo).then_order_by(bar) is equivalent to .order((foo, bar)). This method is only present on boxed queries.

Examples

diesel::insert_into(users)
    .values(&vec![
        name.eq("Saul"),
        name.eq("Steve"),
        name.eq("Stan"),
        name.eq("Stan"),
    ])
    .execute(connection)?;

let data = users.select((name, id))
    .order_by(name.asc())
    .then_order_by(id.desc())
    .load(connection)?;
let expected_data = vec![
    (String::from("Saul"), 3),
    (String::from("Stan"), 6),
    (String::from("Stan"), 5),
    (String::from("Steve"), 4),
];
assert_eq!(expected_data, data);

fn limit(self, limit: i64) -> Limit<Self>

where Self: LimitDsl,

Sets the limit clause of the query.

If there was already a limit clause, it will be overridden.

Example

// Using a limit
let limited = users.select(name)
    .order(id)
    .limit(1)
    .load::<String>(connection)?;

// Without a limit
let no_limit = users.select(name)
    .order(id)
    .load::<String>(connection)?;

assert_eq!(vec!["Sean"], limited);
assert_eq!(vec!["Sean", "Bastien", "Pascal"], no_limit);

fn offset(self, offset: i64) -> Offset<Self>

where Self: OffsetDsl,

Sets the offset clause of the query.

If there was already a offset clause, it will be overridden.

Example

// Using an offset
let offset = users.select(name)
    .order(id)
    .limit(2)
    .offset(1)
    .load::<String>(connection)?;

// No Offset
let no_offset = users.select(name)
    .order(id)
    .limit(2)
    .load::<String>(connection)?;

assert_eq!(vec!["Bastien", "Pascal"], offset);
assert_eq!(vec!["Sean", "Bastien"], no_offset);

fn group_by<GB>(self, group_by: GB) -> GroupBy<Self, GB>

where GB: Expression, Self: GroupByDsl<GB>,

Sets the group by clause of a query.

Note: Queries having a group by clause require a custom select clause. Use QueryDsl::select() to specify one.

If there was already a group by clause, it will be overridden. Grouping by multiple columns can be achieved by passing a tuple of those columns.

Diesel follows postgresql’s group by semantic, this means any column appearing in a group by clause is considered to be aggregated. If a primary key is part of the group by clause every column from the corresponding table is considered to be aggregated. Select clauses cannot mix aggregated and non aggregated expressions.

For group by clauses containing columns from more than one table it is required to call allow_columns_to_appear_in_same_group_by_clause!

Examples

let data = users::table.inner_join(posts::table)
    .group_by(users::id)
    .select((users::name, count(posts::id)))
    .load::<(String, i64)>(connection)?;

assert_eq!(vec![(String::from("Sean"), 2), (String::from("Tess"), 1)], data);

fn having<Predicate>(self, predicate: Predicate) -> Having<Self, Predicate>

where Self: HavingDsl<Predicate>,

Adds to the HAVING clause of a query.

Examples

let data = users::table.inner_join(posts::table)
    .group_by(users::id)
    .having(count(posts::id).gt(1))
    .select((users::name, count(posts::id)))
    .load::<(String, i64)>(connection)?;

assert_eq!(vec![(String::from("Sean"), 2)], data);

fn for_update(self) -> ForUpdate<Self>

where Self: LockingDsl<ForUpdate>,

Adds FOR UPDATE to the end of the select statement.

This method is only available for MySQL and PostgreSQL. SQLite does not provide any form of row locking.

Additionally, .for_update cannot be used on queries with a distinct clause, group by clause, having clause, or any unions. Queries with a FOR UPDATE clause cannot be boxed.

Example

// Executes `SELECT * FROM users FOR UPDATE`
let users_for_update = users::table.for_update().load(connection)?;

fn for_no_key_update(self) -> ForNoKeyUpdate<Self>

where Self: LockingDsl<ForNoKeyUpdate>,

Adds FOR NO KEY UPDATE to the end of the select statement.

This method is only available for PostgreSQL. SQLite does not provide any form of row locking, and MySQL does not support anything finer than row-level locking.

Additionally, .for_no_key_update cannot be used on queries with a distinct clause, group by clause, having clause, or any unions. Queries with a FOR NO KEY UPDATE clause cannot be boxed.

Example

// Executes `SELECT * FROM users FOR NO KEY UPDATE`
let users_for_no_key_update = users::table.for_no_key_update().load(connection)?;

fn for_share(self) -> ForShare<Self>

where Self: LockingDsl<ForShare>,

Adds FOR SHARE to the end of the select statement.

This method is only available for MySQL and PostgreSQL. SQLite does not provide any form of row locking.

Additionally, .for_share cannot be used on queries with a distinct clause, group by clause, having clause, or any unions. Queries with a FOR SHARE clause cannot be boxed.

Example

// Executes `SELECT * FROM users FOR SHARE`
let users_for_share = users::table.for_share().load(connection)?;

fn for_key_share(self) -> ForKeyShare<Self>

where Self: LockingDsl<ForKeyShare>,

Adds FOR KEY SHARE to the end of the select statement.

This method is only available for PostgreSQL. SQLite does not provide any form of row locking, and MySQL does not support anything finer than row-level locking.

Additionally, .for_key_share cannot be used on queries with a distinct clause, group by clause, having clause, or any unions. Queries with a FOR KEY SHARE clause cannot be boxed.

Example

// Executes `SELECT * FROM users FOR KEY SHARE`
let users_for_key_share = users::table.for_key_share().load(connection)?;

fn skip_locked(self) -> SkipLocked<Self>

where Self: ModifyLockDsl<SkipLocked>,

Adds SKIP LOCKED to the end of a FOR UPDATE clause.

This modifier is only supported in PostgreSQL 9.5+ and MySQL 8+.

Example

// Executes `SELECT * FROM users FOR UPDATE SKIP LOCKED`
let user_skipped_locked = users::table.for_update().skip_locked().load(connection)?;

fn no_wait(self) -> NoWait<Self>

where Self: ModifyLockDsl<NoWait>,

Adds NOWAIT to the end of a FOR UPDATE clause.

This modifier is only supported in PostgreSQL 9.5+ and MySQL 8+.

Example

// Executes `SELECT * FROM users FOR UPDATE NOWAIT`
let users_no_wait = users::table.for_update().no_wait().load(connection)?;

fn into_boxed<'a, DB>(self) -> IntoBoxed<'a, Self, DB>

where DB: Backend, Self: BoxedDsl<'a, DB>,

Boxes the pieces of a query into a single type.

This is useful for cases where you want to conditionally modify a query, but need the type to remain the same. The backend must be specified as part of this. It is not possible to box a query and have it be useable on multiple backends.

A boxed query will incur a minor performance penalty, as the query builder can no longer be inlined by the compiler. For most applications this cost will be minimal.

Example

let mut query = users::table.into_boxed();
if let Some(name) = params.get("name") {
    query = query.filter(users::name.eq(name));
}
let users = query.load(connection);

Diesel queries also have a similar problem to Iterator, where returning them from a function requires exposing the implementation of that function. The helper_types module exists to help with this, but you might want to hide the return type or have it conditionally change. Boxing can achieve both.

Example

fn users_by_name(name: &str) -> users::BoxedQuery<DB> {
    users::table.filter(users::name.eq(name)).into_boxed()
}

assert_eq!(Ok(1), users_by_name("Sean").select(users::id).first(connection));
assert_eq!(Ok(2), users_by_name("Tess").select(users::id).first(connection));

fn single_value(self) -> SingleValue<Self>

where Self: SingleValueDsl,

Wraps this select statement in parenthesis, allowing it to be used as an expression.

SQL allows queries such as foo = (SELECT ...), as long as the subselect returns only a single column, and 0 or 1 rows. This method indicates that you expect the query to only return a single value (this will be enforced by adding LIMIT 1).

The SQL type of this will always be Nullable, as the query returns NULL if the table is empty or it otherwise returns 0 rows.

Example

insert_into(posts::table)
    .values(posts::user_id.eq(1))
    .execute(connection)?;
let last_post = posts::table
    .order(posts::id.desc());
let most_recently_active_user = users.select(name)
    .filter(id.nullable().eq(last_post.select(posts::user_id).single_value()))
    .first::<String>(connection)?;
assert_eq!("Sean", most_recently_active_user);

fn nullable(self) -> NullableSelect<Self>

where Self: SelectNullableDsl,

Coerce the SQL type of the select clause to it’s nullable equivalent.

This is useful for writing queries that contain subselects on non null fields comparing them to nullable fields.

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

table! {
    posts {
        id -> Integer,
        by_user -> Nullable<Text>,
    }
}

allow_tables_to_appear_in_same_query!(users, posts);

posts::table.filter(
   posts::by_user.eq_any(users::table.select(users::name).nullable())
).load(connection)?;

Object Safety

This trait is not object safe.

Implementors

impl<S: AliasSource> QueryDsl for Alias<S>

impl<T: Table> QueryDsl for T