Trait diesel::expression::AsExpression

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pub trait AsExpression<T> {
    type Expression: Expression<SqlType = T>;
    fn as_expression(self) -> Self::Expression;
}
Expand description

Converts a type to its representation for use in Diesel’s query builder.

This trait is used directly. Apps should typically use IntoSql instead.

Implementations of this trait will generally do one of 3 things:

  • Return self for types which are already parts of Diesel’s query builder

  • Perform some implicit coercion (for example, allowing now to be used as both Timestamp and Timestamptz.

  • Indicate that the type has data which will be sent separately from the query. This is generally referred as a “bind parameter”. Types which implement ToSql will generally implement AsExpression this way.

Deriving

This trait can be automatically derived for any type which implements ToSql. The type must be annotated with #[sql_type = "SomeType"]. If that annotation appears multiple times, implementations will be generated for each one of them.

This will generate the following impls:

  • impl AsExpression<SqlType> for YourType
  • impl AsExpression<Nullable<SqlType>> for YourType
  • impl AsExpression<SqlType> for &'a YourType
  • impl AsExpression<Nullable<SqlType>> for &'a YourType
  • impl AsExpression<SqlType> for &'a &'b YourType
  • impl AsExpression<Nullable<SqlType>> for &'a &'b YourType

If your type is unsized, you can specify this by adding the annotation #[diesel(not_sized)]. This will skip the impls for non-reference types.

Associated Types

The expression being returned

Required methods

Perform the conversion

Implementations on Foreign Types

Implementors