Queryable.Where Method
Definition
Filters a sequence of values based on a predicate.
Overloads
Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) |
Filters a sequence of values based on a predicate. |
Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) |
Filters a sequence of values based on a predicate. Each element's index is used in the logic of the predicate function. |
Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)
Filters a sequence of values based on a predicate.
public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static System::Linq::IQueryable<TSource> ^ Where(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, bool> ^> ^ predicate);
public static System.Linq.IQueryable<TSource> Where<TSource> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,bool>> predicate);
static member Where : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, bool>> -> System.Linq.IQueryable<'Source>
<Extension()>
Public Function Where(Of TSource) (source As IQueryable(Of TSource), predicate As Expression(Of Func(Of TSource, Boolean))) As IQueryable(Of TSource)
Type Parameters
- TSource
The type of the elements of source
.
Parameters
- source
- IQueryable<TSource>
An IQueryable<T> to filter.
- predicate
- Expression<Func<TSource,Boolean>>
A function to test each element for a condition.
Returns
- IQueryable<TSource>
An IQueryable<T> that contains elements from the input sequence that satisfy the condition specified by predicate
.
Exceptions
source
or predicate
is null
.
Examples
The following code example demonstrates how to use Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) to filter a sequence.
List<string> fruits =
new List<string> { "apple", "passionfruit", "banana", "mango",
"orange", "blueberry", "grape", "strawberry" };
// Get all strings whose length is less than 6.
IEnumerable<string> query =
fruits.AsQueryable().Where(fruit => fruit.Length < 6);
foreach (string fruit in query)
Console.WriteLine(fruit);
/*
This code produces the following output:
apple
mango
grape
*/
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
output.AppendLine(fruit)
Next
MsgBox(output.ToString())
' This code produces the following output:
' apple
' mango
' grape
Remarks
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 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) method generates a MethodCallExpression that represents calling Where<TSource>(IQueryable<TSource>, Expression<Func<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<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 elements from source
that satisfy the condition specified by predicate
.
Applies to
Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)
Filters a sequence of values based on a predicate. Each element's index is used in the logic of the predicate function.
public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static System::Linq::IQueryable<TSource> ^ Where(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, int, bool> ^> ^ predicate);
public static System.Linq.IQueryable<TSource> Where<TSource> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,int,bool>> predicate);
static member Where : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, int, bool>> -> System.Linq.IQueryable<'Source>
<Extension()>
Public Function Where(Of TSource) (source As IQueryable(Of TSource), predicate As Expression(Of Func(Of TSource, Integer, Boolean))) As IQueryable(Of TSource)
Type Parameters
- TSource
The type of the elements of source
.
Parameters
- source
- IQueryable<TSource>
An IQueryable<T> to filter.
- predicate
- Expression<Func<TSource,Int32,Boolean>>
A function to test each element for a condition; the second parameter of the function represents the index of the element in the source sequence.
Returns
- IQueryable<TSource>
An IQueryable<T> that contains elements from the input sequence that satisfy the condition specified by predicate
.
Exceptions
source
or predicate
is null
.
Examples
The following code example demonstrates how to use Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) to filter a sequence based on a predicate that incorporates the index of each element.
int[] numbers = { 0, 30, 20, 15, 90, 85, 40, 75 };
// Get all the numbers that are less than or equal to
// the product of their index in the array and 10.
IEnumerable<int> query =
numbers.AsQueryable()
.Where((number, index) => number <= index * 10);
foreach (int number in query)
Console.WriteLine(number);
/*
This code produces the following output:
0
20
15
40
*/
Dim numbers() As Integer = {0, 30, 20, 15, 90, 85, 40, 75}
' Get all the numbers that are less than or equal to
' the product of their index in the array and 10.
Dim query = numbers.AsQueryable() _
.Where(Function(number, index) number <= index * 10)
' Display the results.
Dim output As New System.Text.StringBuilder
For Each number As Integer In query
output.AppendLine(number)
Next
MsgBox(output.ToString())
' This code produces the following output:
' 0
' 20
' 15
' 40
Remarks
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 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) method generates a MethodCallExpression that represents calling Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,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<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,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 index of each source element is provided as the second argument to predicate
.