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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)

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

source
Type: System.Linq.IQueryable<TSource>
A sequence whose elements to test for a condition.
predicate
Type: System.Linq.Expressions.Expression<Func<TSource, Boolean>>
A function to test each element for a condition.

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.

ExceptionCondition
ArgumentNullException

source or predicate is null.

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.

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.


         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.


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
    */
}


Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

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

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