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//! AST types representing various typed SQL expressions. Almost all types //! implement either [`Expression`](trait.Expression.html) or //! [`AsExpression`](trait.AsExpression.html). //! //! The most common expression to work with is a //! [`Column`](../query_source/trait.Column.html). There are various methods //! that you can call on these, found in //! [`expression_methods`](expression_methods/index.html). You can also call //! numeric operators on types which have been passed to //! [`operator_allowed!`](../macro.operator_allowed!.html) or //! [`numeric_expr!`](../macro.numeric_expr!.html). //! //! Any primitive which implements [`ToSql`](../types/trait.ToSql.html) will //! also implement [`AsExpression`](trait.AsExpression.html), allowing it to be //! used as an argument to any of the methods described here. #[macro_use] #[doc(hidden)] pub mod ops; #[doc(hidden)] pub mod aliased; #[doc(hidden)] pub mod array_comparison; #[doc(hidden)] pub mod bound; #[doc(hidden)] pub mod count; pub mod expression_methods; #[doc(hidden)] pub mod functions; #[doc(hidden)] pub mod grouped; pub mod helper_types; #[doc(hidden)] pub mod nullable; #[doc(hidden)] #[macro_use] pub mod predicates; pub mod sql_literal; /// Reexports various top level functions and core extensions that are too /// generic to export by default. This module exists to conveniently glob import /// in functions where you need them. pub mod dsl { #[doc(inline)] pub use super::count::{count, count_star}; #[doc(inline)] pub use super::functions::date_and_time::*; #[doc(inline)] pub use super::functions::aggregate_ordering::*; #[doc(inline)] pub use super::functions::aggregate_folding::*; #[doc(inline)] pub use super::sql_literal::sql; #[cfg(feature = "postgres")] pub use pg::expression::dsl::*; } pub use self::dsl::*; pub use self::sql_literal::SqlLiteral; use backend::Backend; /// Represents a typed fragment of SQL. Apps should not need to implement this /// type directly, but it may be common to use this as type boundaries. /// Libraries should consider using /// [`infix_predicate!`](../macro.infix_predicate!.html) or /// [`postfix_predicate!`](../macro.postfix_predicate!.html) instead of /// implementing this directly. pub trait Expression { type SqlType; } impl<T: Expression + ?Sized> Expression for Box<T> { type SqlType = T::SqlType; } impl<'a, T: Expression + ?Sized> Expression for &'a T { type SqlType = T::SqlType; } /// Describes how a type can be represented as an expression for a given type. /// These types couldn't just implement [`Expression`](trait.Expression.html) /// directly, as many things can be used as an expression of multiple types. /// (`String` for example, can be used as either /// [`VarChar`](../types/struct.VarChar.html) or /// [`Text`](../types/struct.Text.html)). /// /// This trait allows us to use primitives on the right hand side of various /// expressions. For example `name.eq("Sean")` pub trait AsExpression<T> { type Expression: Expression<SqlType=T>; fn as_expression(self) -> Self::Expression; } impl<T: Expression> AsExpression<T::SqlType> for T { type Expression = Self; fn as_expression(self) -> Self { self } } /// Indicates that an expression can be selected from a source. The second type /// argument is optional, but is used to indicate that the right side of a left /// outer join is nullable, even if it wasn't before. /// /// Columns will implement this for their table. Certain special types, like /// `CountStar` and [`Bound`](bound/struct.Bound.html) will implement this for /// all sources. All other expressions will inherit this from their children. pub trait SelectableExpression< QS, Type = <Self as Expression>::SqlType, >: Expression { } impl<T: ?Sized, ST, QS> SelectableExpression<QS, ST> for Box<T> where T: SelectableExpression<QS, ST>, Box<T>: Expression, { } impl<'a, T: ?Sized, ST, QS> SelectableExpression<QS, ST> for &'a T where T: SelectableExpression<QS, ST>, &'a T: Expression, { } /// Marker trait to indicate that an expression does not include any aggregate /// functions. Used to ensure that aggregate expressions aren't mixed with /// non-aggregate expressions in a select clause, and that they're never /// included in a where clause. pub trait NonAggregate: Expression { } impl<T: NonAggregate + ?Sized> NonAggregate for Box<T> { } impl<'a, T: NonAggregate + ?Sized> NonAggregate for &'a T { } use query_builder::QueryFragment; /// Helper trait used when boxing expressions. This exists to work around the /// fact that Rust will not let us use non-core types as bounds on a trait /// object (you could not return `Box<Expression+NonAggregate>`) pub trait BoxableExpression<QS, ST, DB> where DB: Backend, Self: Expression, Self: SelectableExpression<QS, ST>, Self: NonAggregate, Self: QueryFragment<DB>, {} impl<QS, T, ST, DB> BoxableExpression<QS, ST, DB> for T where DB: Backend, T: Expression, T: SelectableExpression<QS, ST>, T: NonAggregate, T: QueryFragment<DB>, { }