Queryable.All<TSource> Method

Determines whether all the elements of a sequence satisfy a condition.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function All(Of TSource) ( _
    source As IQueryable(Of TSource), _
    predicate As Expression(Of Func(Of TSource, Boolean)) _
) As Boolean
public static bool All<TSource>(
    this IQueryable<TSource> source,
    Expression<Func<TSource, bool>> predicate
)

Type Parameters

  • TSource
    The type of the elements of source.

Parameters

Return Value

Type: System.Boolean
true if every element of the source sequence passes the test in the specified predicate, or if the sequence is empty; otherwise, false.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<TSource>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception Condition
ArgumentNullException

source or predicate is nulla null reference (Nothing in Visual Basic).

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 All<TSource>(IQueryable<TSource>, Expression<Func<TSource, Boolean>>) method generates a MethodCallExpression that represents calling All<TSource>(IQueryable<TSource>, Expression<Func<TSource, Boolean>>) 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 All<TSource>(IQueryable<TSource>, Expression<Func<TSource, Boolean>>) depends on the implementation of the source parameter's type. The expected behavior is that it determines if all the elements in source satisfy the condition in predicate.

Examples

The following code example demonstrates how to use All<TSource>(IQueryable<TSource>, Expression<Func<TSource, Boolean>>) to determine whether all the elements in a sequence satisfy a condition.

   Sub AllEx()
      ' Create an array of Pets.
      Dim pets() As Pet = _
          {New Pet With {.Name = "Barley", .Age = 10}, _
           New Pet With {.Name = "Boots", .Age = 4}, _
           New Pet With {.Name = "Whiskers", .Age = 6}}

      ' Determine whether all pet names in the array start with 'B'.
      Dim allStartWithB As Boolean = _
          pets.AsQueryable().All(Function(pet) pet.Name.StartsWith("B"))

      outputBlock.Text &= String.Format( _
          "{0} pet names start with 'B'.", _
          IIf(allStartWithB, "All", "Not all")) & vbCrLf
   End Sub

   Public Structure Pet
      Dim Name As String
      Dim Age As Integer
   End Structure

   ' This code produces the following output:
   '
   '  Not all pet names start with 'B'. 

         class Pet
         {
            public string Name { get; set; }
            public int Age { get; set; }
         }

         public static void AllEx1(System.Windows.Controls.TextBlock outputBlock)
         {
            // Create an array of Pets.
            Pet[] pets = { new Pet { Name="Barley", Age=10 },
                               new Pet { Name="Boots", Age=4 },
                               new Pet { Name="Whiskers", Age=6 } };

            // Determine whether all pet names in the array start with 'B'.
            bool allStartWithB =
                pets.AsQueryable().All(pet => pet.Name.StartsWith("B"));

            outputBlock.Text += String.Format(
                "{0} pet names start with 'B'.",
                allStartWithB ? "All" : "Not all") + "\n";
         }

         // This code produces the following output:
         //
         //  Not all pet names start with 'B'. 

The Boolean value that the All<TSource>(IQueryable<TSource>, Expression<Func<TSource, Boolean>>) method returns is typically used in the predicate of a where clause (Where clause in Visual Basic) or a direct call to the Where method. The following example demonstrates this use of the All method.

Structure Pet
   Public Name As String
   Public Age As Integer
End Structure

Structure Person
   Public LastName As String
   Public Pets() As Pet
End Structure

Sub AllEx2(ByVal outputBlock As System.Windows.Controls.TextBlock)
   Dim people As New List(Of Person)(New Person() _
       {New Person With {.LastName = "Haas", _
                         .Pets = New Pet() {New Pet With {.Name = "Barley", .Age = 10}, _
                                            New Pet With {.Name = "Boots", .Age = 14}, _
                                            New Pet With {.Name = "Whiskers", .Age = 6}}}, _
         New Person With {.LastName = "Fakhouri", _
                          .Pets = New Pet() {New Pet With {.Name = "Snowball", .Age = 1}}}, _
         New Person With {.LastName = "Antebi", _
                          .Pets = New Pet() {New Pet With {.Name = "Belle", .Age = 8}}}, _
         New Person With {.LastName = "Philips", _
                          .Pets = New Pet() {New Pet With {.Name = "Sweetie", .Age = 2}, _
                                             New Pet With {.Name = "Rover", .Age = 13}}}})

   ' Determine which people have pets that are all older than 5.
   Dim names = From person In people _
               Where person.Pets.AsQueryable().All(Function(pet) pet.Age > 5) _
               Select person.LastName

   For Each name As String In names
      outputBlock.Text &= name & vbCrLf
   Next

   ' This code produces the following output:
   '
   ' Haas
   ' Antebi

End Sub
class Pet
{
   public string Name { get; set; }
   public int Age { get; set; }
}
class Person
{
   public string LastName { get; set; }
   public Pet[] Pets { get; set; }
}

public static void AllEx2(System.Windows.Controls.TextBlock outputBlock)
{
   List<Person> people = new List<Person>
           { new Person { LastName = "Haas",
                          Pets = new Pet[] { new Pet { Name="Barley", Age=10 },
                                             new Pet { Name="Boots", Age=14 },
                                             new Pet { Name="Whiskers", Age=6 }}},
             new Person { LastName = "Fakhouri",
                          Pets = new Pet[] { new Pet { Name = "Snowball", Age = 1}}},
             new Person { LastName = "Antebi",
                          Pets = new Pet[] { new Pet { Name = "Belle", Age = 8} }},
             new Person { LastName = "Philips",
                          Pets = new Pet[] { new Pet { Name = "Sweetie", Age = 2},
                                             new Pet { Name = "Rover", Age = 13}} }
           };

   // Determine which people have pets that are all older than 5.
   IEnumerable<string> names = from person in people
                               where person.Pets.AsQueryable().All(pet => pet.Age > 5)
                               select person.LastName;

   foreach (string name in names)
      outputBlock.Text += name + "\n";

   /* This code produces the following output:
    * 
    * Haas
    * Antebi
    */
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.