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use backend::Backend;
use expression::*;
use query_builder::*;
use query_source::Table;
use result::QueryResult;
use sql_types::IntoNullable;
#[derive(Debug, Copy, Clone, DieselNumericOps)]
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)
}
}
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> NonAggregate for Nullable<T>
where
T: NonAggregate,
Nullable<T>: Expression,
{
}
impl<T, QS> SelectableExpression<QS> for Nullable<T>
where
Self: AppearsOnTable<QS>,
T: SelectableExpression<QS>,
QS: Table,
{
}