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.