Queryable.Where Method

Definition

Namespace:

System.Linq

Assemblies:

netstandard.dll, System.Linq.Queryable.dll

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>>)

Source:

Queryable.cs

Filters a sequence of values based on a predicate.

C#

public static System.Linq.IQueryable<TSource> Where<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,bool>> predicate);

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

ArgumentNullException

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.

C#

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
*/

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.

Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)

Source:

Queryable.cs

Filters a sequence of values based on a predicate. Each element's index is used in the logic of the predicate function.

C#

public static System.Linq.IQueryable<TSource> Where<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,int,bool>> predicate);

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

ArgumentNullException

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.

C#

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
*/

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.