Trait diesel::query_source::AppearsInFromClause
source · pub trait AppearsInFromClause<QS> {
type Count;
}
Expand description
Determines how many times Self
appears in QS
This trait is primarily used to determine whether or not a column is selectable from a given from clause. A column can be selected if its table appears in the from clause exactly once.
We do not allow the same table to appear in a query multiple times in any context where referencing that table would be ambiguous (depending on the context and backend being used, this may or may not be something that would otherwise result in a runtime error).
Required Associated Types§
Implementors§
source§impl<From, T> AppearsInFromClause<T> for SelectStatement<From>where
From: AsQuerySource,
From::QuerySource: AppearsInFromClause<T> + QuerySource,
impl<From, T> AppearsInFromClause<T> for SelectStatement<From>where
From: AsQuerySource,
From::QuerySource: AppearsInFromClause<T> + QuerySource,
Allow SelectStatement<From>
to act as if it were From
as long as
no other query methods have been called on it