Queryable.Where(Of TSource) Method (IQueryable(Of TSource), Expression(Of Func(Of TSource, Boolean)))


The .NET API Reference documentation has a new home. Visit the .NET API Browser on docs.microsoft.com to see the new experience.

Filters a sequence of values based on a predicate.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)

Public Shared Function Where(Of TSource) (
	source As IQueryable(Of TSource),
	predicate As Expression(Of Func(Of TSource, Boolean))
) As IQueryable(Of TSource)


Type: System.Linq.IQueryable(Of TSource)

An IQueryable(Of T) to filter.

Type: System.Linq.Expressions.Expression(Of Func(Of TSource, Boolean))

A function to test each element for a condition.

Return Value

Type: System.Linq.IQueryable(Of TSource)

An IQueryable(Of T) that contains elements from the input sequence that satisfy the condition specified by predicate.

Type Parameters


The type of the elements of source.

Exception Condition

source or predicate is null.

This method has at least one parameter of type Expression(Of TDelegate) whose type argument is one of the Func(Of T, TResult) types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression(Of TDelegate).

The Where(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Boolean))) method generates a MethodCallExpression that represents calling Where(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Boolean))) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery(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 Where(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Boolean))) depends on the implementation of the type of the source parameter. The expected behavior is that it returns the elements from source that satisfy the condition specified by predicate.

The following code example demonstrates how to use Where(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Boolean))) to filter a sequence.

Dim fruits As New List(Of String)(New String() _
                        {"apple", "passionfruit", "banana", "mango", _
                         "orange", "blueberry", "grape", "strawberry"})

' Get all strings whose length is less than 6.
Dim query = fruits.AsQueryable().Where(Function(fruit) fruit.Length < 6)

' Display the results.
Dim output As New System.Text.StringBuilder
For Each fruit As String In query

' This code produces the following output:

' apple
' mango
' grape

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
Return to top