Queryable.Count メソッド

定義

シーケンス内の要素数を返します。Returns the number of elements in a sequence.

オーバーロード

Count<TSource>(IQueryable<TSource>)

シーケンス内の要素数を返します。Returns the number of elements in a sequence.

Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)

指定したシーケンス内の、条件を満たす要素の数を返します。Returns the number of elements in the specified sequence that satisfies a condition.

Count<TSource>(IQueryable<TSource>)

シーケンス内の要素数を返します。Returns the number of elements in a sequence.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static int Count(System::Linq::IQueryable<TSource> ^ source);
public static int Count<TSource> (this System.Linq.IQueryable<TSource> source);
static member Count : System.Linq.IQueryable<'Source> -> int
<Extension()>
Public Function Count(Of TSource) (source As IQueryable(Of TSource)) As Integer

型パラメーター

TSource

source の要素の型。The type of the elements of source.

パラメーター

source
IQueryable<TSource>

カウントする要素が格納されている IQueryable<T>The IQueryable<T> that contains the elements to be counted.

戻り値

Int32

入力シーケンス内の要素数。The number of elements in the input sequence.

例外

sourcenull です。source is null.

source 内の要素数が MaxValue を超えています。The number of elements in source is larger than MaxValue.

次のコード例は、Count<TSource>(IQueryable<TSource>) を使用してシーケンス内の要素をカウントする方法を示しています。The following code example demonstrates how to use Count<TSource>(IQueryable<TSource>) to count the elements in a sequence.

string[] fruits = { "apple", "banana", "mango",
                    "orange", "passionfruit", "grape" };

int numberOfFruits = fruits.AsQueryable().Count();

Console.WriteLine(
    "There are {0} items in the array.",
    numberOfFruits);

// This code produces the following output:
//
// There are 6 items in the array.

Dim fruits() As String = {"apple", "banana", "mango", _
                    "orange", "passionfruit", "grape"}

Dim numberOfFruits As Integer = fruits.AsQueryable().Count()

MsgBox(String.Format( _
    "There are {0} items in the array.", _
    numberOfFruits))

' This code produces the following output:
'
' There are 6 items in the array. 

注釈

Count<TSource>(IQueryable<TSource>) メソッドは、構築されたジェネリックメソッドとしての呼び出し Count<TSource>(IQueryable<TSource>) 自体を表す MethodCallExpression を生成します。The Count<TSource>(IQueryable<TSource>) method generates a MethodCallExpression that represents calling Count<TSource>(IQueryable<TSource>) itself as a constructed generic method. 次に、source パラメーターの Provider プロパティによって表される IQueryProviderExecute<TResult>(Expression) メソッドに MethodCallExpression を渡します。It then passes the MethodCallExpression to the Execute<TResult>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

Count<TSource>(IQueryable<TSource>) の呼び出しを表す式ツリーを実行した結果として発生するクエリ動作は、source パラメーターの型の実装によって異なります。The query behavior that occurs as a result of executing an expression tree that represents calling Count<TSource>(IQueryable<TSource>) depends on the implementation of the type of the source parameter. 期待される動作は、source内の項目数をカウントすることです。The expected behavior is that it counts the number of items in source.

Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)

指定したシーケンス内の、条件を満たす要素の数を返します。Returns the number of elements in the specified sequence that satisfies a condition.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static int Count(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, bool> ^> ^ predicate);
public static int Count<TSource> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,bool>> predicate);
static member Count : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, bool>> -> int
<Extension()>
Public Function Count(Of TSource) (source As IQueryable(Of TSource), predicate As Expression(Of Func(Of TSource, Boolean))) As Integer

型パラメーター

TSource

source の要素の型。The type of the elements of source.

パラメーター

source
IQueryable<TSource>

カウントする要素が格納されている IQueryable<T>An IQueryable<T> that contains the elements to be counted.

predicate
Expression<Func<TSource,Boolean>>

各要素が条件を満たしているかどうかをテストする関数。A function to test each element for a condition.

戻り値

Int32

述語関数の条件を満たす、シーケンス内の要素数。The number of elements in the sequence that satisfies the condition in the predicate function.

例外

source または predicatenull です。source or predicate is null.

source 内の要素数が MaxValue を超えています。The number of elements in source is larger than MaxValue.

次のコード例は、Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) を使用して、条件を満たすシーケンス内の要素をカウントする方法を示しています。The following code example demonstrates how to use Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) to count the elements in a sequence that satisfy a condition.

class Pet
{
    public string Name { get; set; }
    public bool Vaccinated { get; set; }
}

public static void CountEx2()
{
    // Create an array of Pet objects.
    Pet[] pets = { new Pet { Name="Barley", Vaccinated=true },
                   new Pet { Name="Boots", Vaccinated=false },
                   new Pet { Name="Whiskers", Vaccinated=false } };

    // Count the number of unvaccinated pets in the array.
    int numberUnvaccinated =
        pets.AsQueryable().Count(p => p.Vaccinated == false);

    Console.WriteLine(
        "There are {0} unvaccinated animals.",
        numberUnvaccinated);
}

// This code produces the following output:
//
// There are 2 unvaccinated animals.

Structure Pet
    Public Name As String
    Public Vaccinated As Boolean
End Structure

Shared Sub CountEx2()
    ' Create an array of Pet objects.
    Dim pets() As Pet = {New Pet With {.Name = "Barley", .Vaccinated = True}, _
                   New Pet With {.Name = "Boots", .Vaccinated = False}, _
                   New Pet With {.Name = "Whiskers", .Vaccinated = False}}

    ' Count the number of unvaccinated pets in the array.
    Dim numberUnvaccinated As Integer = pets.AsQueryable().Count(Function(p) p.Vaccinated = False)

    MsgBox(String.Format("There are {0} unvaccinated animals.", numberUnvaccinated))
End Sub

' This code produces the following output:
'
' There are 2 unvaccinated animals.

注釈

このメソッドには、型引数が Func<T,TResult> 型の1つである Expression<TDelegate> 型のパラメーターが少なくとも1つ含まれています。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. これらのパラメーターでは、ラムダ式を渡すことができ、Expression<TDelegate>にコンパイルされます。For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) メソッドは、構築されたジェネリックメソッドとしての呼び出し Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 自体を表す MethodCallExpression を生成します。The Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) method generates a MethodCallExpression that represents calling Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) itself as a constructed generic method. 次に、source パラメーターの Provider プロパティによって表される IQueryProviderExecute<TResult>(Expression) メソッドに MethodCallExpression を渡します。It then passes the MethodCallExpression to the Execute<TResult>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) の呼び出しを表す式ツリーを実行した結果として発生するクエリ動作は、source パラメーターの型の実装によって異なります。The query behavior that occurs as a result of executing an expression tree that represents calling Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) depends on the implementation of the type of the source parameter. 期待される動作は、predicateによって指定された条件を満たす source 内の項目の数をカウントすることです。The expected behavior is that it counts the number of items in source that satisfy the condition specified by predicate.

適用対象