Queryable::Single<TSource> Method (IQueryable<TSource>^, Expression<Func<TSource, Boolean>^>^)
Returns the only element of a sequence that satisfies a specified condition, and throws an exception if more than one such element exists.
Assembly: System.Core (in System.Core.dll)
public: generic<typename TSource> [ExtensionAttribute] static TSource Single( IQueryable<TSource>^ source, Expression<Func<TSource, bool>^>^ predicate )
Parameters
- source
-
Type:
System.Linq::IQueryable<TSource>^
An IQueryable<T> to return a single element from.
- predicate
-
Type:
System.Linq.Expressions::Expression<Func<TSource, Boolean>^>^
A function to test an element for a condition.
Return Value
Type: TSourceThe single element of the input sequence that satisfies the condition in predicate.
Type Parameters
- TSource
The type of the elements of source.
| Exception | Condition |
|---|---|
| ArgumentNullException | source or predicate is null. |
| InvalidOperationException | No element satisfies the condition in predicate. -or- More than one element satisfies the condition in predicate. -or- The source sequence is empty. |
This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T, TResult> types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.
The Single<TSource>(IQueryable<TSource>^, Expression<Func<TSource, Boolean>^>^) method generates a MethodCallExpression that represents calling Single<TSource>(IQueryable<TSource>^, Expression<Func<TSource, Boolean>^>^) itself as a constructed generic method. It then passes the MethodCallExpression to the Execute<TResult>(Expression^) method of the IQueryProvider represented by the Provider property of the source parameter.
The query behavior that occurs as a result of executing an expression tree that represents calling Single<TSource>(IQueryable<TSource>^, Expression<Func<TSource, Boolean>^>^) depends on the implementation of the type of the source parameter. The expected behavior is that it returns the only element in source that satisfies the condition specified by predicate.
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1