방법: 기본 형식의 컬렉션을 반환하는 쿼리 실행(Entity Framework)

이 항목에서는 기본 형식의 컬렉션을 반환하는 쿼리를 실행하는 방법에 대한 예제를 제공합니다. 단일 개체만 반환하려면 쿼리를 기반으로 First, FirstOrDefault, Single 및 SingleOrDefault 메서드 중 하나를 사용합니다.

또한 동일한 예제에서 다음의 Entity Framework 쿼리 기술을 각각 사용한 경우도 보여 줍니다.

• LINQ to Entities

• ObjectQuery<T>가 포함된 Entity SQL

• ObjectQuery<T>의 쿼리 작성기 메서드

이 항목의 예제는 Adventure Works Sales 모델을 기반으로 합니다. 이 항목의 코드를 실행하려면 프로젝트에 Adventure Works Sales 모델을 추가하고 프로젝트에서 Entity Framework를 사용하도록 구성해야 합니다. 자세한 내용은 방법: 엔터티 데이터 모델 마법사 사용(Entity Framework) 또는 방법: Entity Framework 프로젝트 수동 구성 및 방법: 엔터티 데이터 모델 수동 정의(Entity Framework)를 참조하십시오.

예제

다음은 LINQ to Entities 예제입니다.

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);
    }
}

다음은 Entity SQL 예제입니다.

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);
    }
}

다음은 쿼리 작성기 메서드 예제입니다.

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);
    }
}

참고 항목

작업

방법: 엔터티 형식 개체를 반환하는 쿼리 실행(Entity Framework)
방법: 익명 형식의 컬렉션을 반환하는 쿼리 실행(Entity Framework)
방법: 매개 변수가 있는 쿼리 실행(Entity Framework)

개념

쿼리 작성기 메서드(Entity Framework)