| use crate::backend::Backend; |
| use crate::expression::*; |
| use crate::query_builder::*; |
| use crate::query_source::Table; |
| use crate::result::QueryResult; |
| use crate::sql_types::IntoNullable; |
| |
| #[derive(Debug, Copy, Clone, DieselNumericOps, NonAggregate)] |
| pub struct Nullable<T>(T); |
| |
| impl<T> Nullable<T> { |
| pub fn new(expr: T) -> Self { |
| Nullable(expr) |
| } |
| } |
| |
| impl<T> Expression for Nullable<T> |
| where |
| T: Expression, |
| <T as Expression>::SqlType: IntoNullable, |
| { |
| type SqlType = <<T as Expression>::SqlType as IntoNullable>::Nullable; |
| } |
| |
| impl<T, DB> QueryFragment<DB> for Nullable<T> |
| where |
| DB: Backend, |
| T: QueryFragment<DB>, |
| { |
| fn walk_ast(&self, pass: AstPass<DB>) -> QueryResult<()> { |
| self.0.walk_ast(pass) |
| } |
| } |
| |
| /// Nullable can be used in where clauses everywhere, but can only be used in |
| /// select clauses for outer joins. |
| impl<T, QS> AppearsOnTable<QS> for Nullable<T> |
| where |
| T: AppearsOnTable<QS>, |
| Nullable<T>: Expression, |
| { |
| } |
| |
| impl<T: QueryId> QueryId for Nullable<T> { |
| type QueryId = T::QueryId; |
| |
| const HAS_STATIC_QUERY_ID: bool = T::HAS_STATIC_QUERY_ID; |
| } |
| |
| impl<T, QS> SelectableExpression<QS> for Nullable<T> |
| where |
| Self: AppearsOnTable<QS>, |
| T: SelectableExpression<QS>, |
| QS: Table, |
| { |
| } |