方法: プリミティブ型のコレクションを返すクエリを実行する (Entity Framework)

このトピックでは、プリミティブ型のコレクションを返すクエリの実行方法について説明します。 オブジェクトを 1 つだけ返すには、クエリの先頭に、First、FirstOrDefault、Single、または SingleOrDefault のいずれかのメソッドを使用します。

次の各 Entity Framework クエリ テクノロジを使用して同じ処理を実行する例を示します。

• LINQ to Entities

• Entity SQL と ObjectQuery<T>

• ObjectQuery<T> のクエリ ビルダー メソッド

このトピックの例には、Adventure Works Sales Model が使用されています。このトピックのコードを実行するには、あらかじめプロジェクトに Adventure Works Sales Model を追加し、Entity Framework を使用するようにプロジェクトを構成しておく必要があります。詳細については、「Entity Data Model ウィザードを使用する方法 (Entity Framework)」、または「Entity Framework プロジェクトを手動で構成する方法」、および「Entity Data Model を手動で定義する方法 (Entity Framework)」を参照してください。

例

以下は LINQ to Entities の例です。

Dim contactId As Integer = 377

Using context As New AdventureWorksEntities()
    ' Select a value. 
    Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders

    Dim orderQuery As IQueryable(Of Int32) = From order In orders _
        Where order.Contact.ContactID = contactId _
        Select order.PurchaseOrderNumber.Length

    ' Iterate through the collection of values. 
    For Each result As Int32 In orderQuery
        Console.WriteLine("{0}", result)
    Next

    ' Use a nullable DateTime value because ShipDate can be null. 
    Dim shipDateQuery As IQueryable(Of System.Nullable(Of DateTime)) = From order In orders _
        Where order.Contact.ContactID = contactId _
        Select order.ShipDate

    ' Iterate through the collection of values. 
    For Each shipDate As System.Nullable(Of DateTime) In shipDateQuery
        Dim shipDateMessage As String = "date not set"

        If shipDate IsNot Nothing Then
            shipDateMessage = shipDate.ToString()
        End If
        Console.WriteLine("Ship Date: {0}.", shipDateMessage)
    Next
End Using

int contactId = 377;

using (AdventureWorksEntities context
    = new AdventureWorksEntities())
{
    // Select a value.
    ObjectSet<SalesOrderHeader> orders
        = context.SalesOrderHeaders;

    IQueryable<Int32> orderQuery =
        from order in orders
        where order.Contact.ContactID == contactId
        select order.PurchaseOrderNumber.Length;

    // Iterate through the collection of values.
    foreach (Int32 result in orderQuery)
    {
        Console.WriteLine("{0}", result);
    }

    // Use a nullable DateTime value because ShipDate can be null.
    IQueryable<DateTime?> shipDateQuery =
        from order in orders
        where order.Contact.ContactID == contactId
        select order.ShipDate;

    // Iterate through the collection of values.
    foreach (DateTime? shipDate in shipDateQuery)
    {
        string shipDateMessage = "date not set";

        if (shipDate != null)
        {
            shipDateMessage = shipDate.ToString();
        }
        Console.WriteLine("Ship Date: {0}.", shipDateMessage);
    }
}

以下は Entity SQL の例です。

Dim contactId As Integer = 377

Using context As New AdventureWorksEntities()
    Dim orderQueryString As String = "SELECT VALUE Length(order.PurchaseOrderNumber) FROM " & _
        " AdventureWorksEntities.SalesOrderHeaders AS order WHERE order.CustomerID = @contactId"
    Dim shipDateQueryString As String = "SELECT VALUE order.ShipDate" & _
        " FROM AdventureWorksEntities.SalesOrderHeaders AS order WHERE order.CustomerID = @contactId"

    ' Use the SelectValue method to select a value. 
    Dim orderQuery As New ObjectQuery(Of Int32)(orderQueryString, context, MergeOption.NoTracking)
    orderQuery.Parameters.Add(New ObjectParameter("contactId", contactId))

    ' Iterate through the collection of values. 
    For Each result As Int32 In orderQuery
        Console.WriteLine("{0}", result)
    Next

    ' Use a nullable DateTime value because ShipDate can be null. 
    Dim shipDateQuery As New ObjectQuery(Of Nullable(Of DateTime))(shipDateQueryString, context, MergeOption.NoTracking)
    shipDateQuery.Parameters.Add(New ObjectParameter("contactId", contactId))

    ' Iterate through the collection of values. 
    For Each shipDate As Nullable(Of DateTime) In shipDateQuery
        Dim shipDateMessage As String = "date not set"

        If shipDate IsNot Nothing Then
            shipDateMessage = shipDate.ToString()
        End If
        Console.WriteLine("Ship Date: {0}.", shipDateMessage)
    Next
End Using

int contactId = 377;

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    string orderQueryString = @"SELECT VALUE Length(order.PurchaseOrderNumber)
        FROM AdventureWorksEntities.SalesOrderHeaders AS order
        WHERE order.CustomerID = @contactId";
    string shipDateQueryString = @"SELECT VALUE order.ShipDate
        FROM AdventureWorksEntities.SalesOrderHeaders AS order
        WHERE order.CustomerID = @contactId";

    // Use the SelectValue method to select a value.
    ObjectQuery<Int32> orderQuery =
        new ObjectQuery<Int32>(orderQueryString,
            context, MergeOption.NoTracking);
    orderQuery.Parameters.Add(
        new ObjectParameter("contactId", contactId));

    // Iterate through the collection of values.
    foreach (Int32 result in orderQuery)
    {
        Console.WriteLine("{0}", result);
    }

    // Use a nullable DateTime value because ShipDate can be null.
    ObjectQuery<Nullable<DateTime>> shipDateQuery =
        new ObjectQuery<Nullable<DateTime>>(shipDateQueryString,
    context, MergeOption.NoTracking);
    shipDateQuery.Parameters.Add(
        new ObjectParameter("contactId", contactId));

    // Iterate through the collection of values.
    foreach (Nullable<DateTime> shipDate in shipDateQuery)
    {
        string shipDateMessage = "date not set";

        if (shipDate != null)
        {
            shipDateMessage = shipDate.ToString();
        }
        Console.WriteLine("Ship Date: {0}.", shipDateMessage);
    }
}

以下は、クエリ ビルダー メソッドの例です。

Dim contactId As Integer = 377

Using context As New AdventureWorksEntities()
    ' Use the SelectValue method to select a value. 
    Dim orderQuery As ObjectQuery(Of Int32) = context.SalesOrderHeaders.Where("it.CustomerID = @contactId", _
                        New ObjectParameter("contactId", contactId)).SelectValue(Of Int32)("Length(it.PurchaseOrderNumber)")

    ' Iterate through the collection of values. 
    For Each result As Int32 In orderQuery
        Console.WriteLine("{0}", result)
    Next

    ' Use a nullable DateTime value because ShipDate can be null. 
    Dim shipDateQuery As ObjectQuery(Of Nullable(Of DateTime)) = _
        context.SalesOrderHeaders.Where("it.CustomerID = @contactId", _
            New ObjectParameter("contactId", contactId)).SelectValue(Of Nullable(Of DateTime))("it.ShipDate")

    ' Iterate through the collection of values. 
    For Each shipDate As Nullable(Of DateTime) In shipDateQuery
        Dim shipDateMessage As String = "date not set"

        If shipDate IsNot Nothing Then
            shipDateMessage = shipDate.ToString()
        End If
        Console.WriteLine("Ship Date: {0}.", shipDateMessage)
    Next
End Using

int contactId = 377;

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    // Use the SelectValue method to select a value.
    ObjectQuery<Int32> orderQuery =
        context.SalesOrderHeaders
        .Where("it.CustomerID = @contactId",
        new ObjectParameter("contactId", contactId))
        .SelectValue<Int32>("Length(it.PurchaseOrderNumber)");

    // Iterate through the collection of values.
    foreach (Int32 result in orderQuery)
    {
        Console.WriteLine("{0}", result);
    }

    // Use a nullable DateTime value because ShipDate can be null.
    ObjectQuery<Nullable<DateTime>> shipDateQuery =
        context.SalesOrderHeaders
        .Where("it.CustomerID = @contactId",
            new ObjectParameter("contactId", contactId))
        .SelectValue<Nullable<DateTime>>("it.ShipDate");

    // Iterate through the collection of values.
    foreach (Nullable<DateTime> shipDate in shipDateQuery)
    {
        string shipDateMessage = "date not set";

        if (shipDate != null)
        {
            shipDateMessage = shipDate.ToString();
        }
        Console.WriteLine("Ship Date: {0}.", shipDateMessage);
    }
}

参照

処理手順

方法: エンティティ型オブジェクトを返すクエリを実行する (Entity Framework)
方法: 匿名型のコレクションを返すクエリを実行する (Entity Framework)
パラメーター化クエリを実行する方法 (Entity Framework)

概念

クエリ ビルダー メソッド (Entity Framework)