Queryable::SingleOrDefault<TSource> Method (IQueryable<TSource>, Expression<Func<TSource, Boolean>>)
Returns the only element of a sequence that satisfies a specified condition or a default value if no such element exists; this method throws an exception if more than one element satisfies the condition.
Assembly: System.Core (in System.Core.dll)
[ExtensionAttribute] public: generic<typename TSource> static TSource SingleOrDefault( IQueryable<TSource>^ source, Expression<Func<TSource, bool>^>^ predicate )
The type of the elements of source.
The single element of the input sequence that satisfies the condition in predicate, or default(TSource) if no such element is found.
Usage NoteIn Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<>. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).
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 method generates a MethodCallExpression that represents calling 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 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, or a default value if no such element exists.
The following code example demonstrates how to use to select the only element of an array that satisfies a condition. The second query demonstrates that returns a default value when the sequence does not contain exactly one element that satisfies the condition.