방법: 쿼리 결과 프로젝션(WCF Data Services)

  • 아티클

프로젝션은 엔터티의 특정 속성만 응답에서 반환되도록 지정하여 쿼리에서 반환되는 데이터의 양을 줄이는 메커니즘을 제공합니다. $select 쿼리 옵션을 사용하거나 LINQ 쿼리에서 select 절(Visual Basic에서는 Select)을 사용하여 WCF Data Services 쿼리의 결과에 대해 프로젝션을 수행할 수 있습니다. 자세한 내용은 데이터 서비스 쿼리(WCF Data Services)를 참조하십시오.

이 항목의 예제에서는 Northwind 샘플 데이터 서비스 및 자동 생성된 클라이언트 데이터 서비스 클래스를 사용합니다. 이 서비스 및 클라이언트 데이터 클래스는 WCF Data Services 퀵 스타트를 완료하면 만들어집니다.

예제

다음 예제에서는 Customers 엔터티를 새로운 CustomerAddress 형식으로 프로젝션하는 LINQ 쿼리를 보여 줍니다. 이 형식에는 주소 관련 속성과 ID 속성만 포함됩니다. 이 CustomerAddress 클래스는 클라이언트에서 정의되며 클라이언트 라이브러리가 엔터티 형식으로 인식할 수 있도록 특성이 지정됩니다.

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

' Define an anonymous LINQ query that projects the Customers type into 
' a CustomerAddress type that contains only address properties.
Dim query = From c In context.Customers _
                Where c.Country = "Germany" _
                Select New CustomerAddress With { _
                    .CustomerID = c.CustomerID, _
                    .Address = c.Address, _
                    .City = c.City, _
                    .Region = c.Region, _
                    .PostalCode = c.PostalCode, _
                    .Country = c.Country}

Try
    ' Enumerate over the query result, which is executed implicitly.
    For Each item In query
        ' Modify the address and mark the object as updated.
        item.Address += " #101"
        context.UpdateObject(item)

        ' Write out the current values.
        Console.WriteLine("Customer ID: {0} \r\nStreet: {1} " _
                & "\r\nCity: {2} \r\nState: {3} \r\nZip Code: {4} \r\nCountry: {5}", _
                item.CustomerID, item.Address, item.City, item.Region, _
                item.PostalCode, item.Country)
    Next

    ' Save changes to the data service.
    context.SaveChanges()
Catch ex As DataServiceQueryException
    Throw New ApplicationException( _
            "An error occurred during query execution.", ex)
End Try

// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);

// Define an anonymous LINQ query that projects the Customers type into 
// a CustomerAddress type that contains only address properties.
var query = from c in context.Customers
            where c.Country == "Germany"
            select new CustomerAddress { 
                CustomerID = c.CustomerID, 
                Address = c.Address, 
                City = c.City, 
                Region = c.Region,
                PostalCode = c.PostalCode, 
                Country = c.Country};

try
{
    // Enumerate over the query result, which is executed implicitly.
    foreach (var item in query)
    {
        // Modify the address and mark the object as updated.
        item.Address += " #101";
        context.UpdateObject(item);

        // Write out the current values.
        Console.WriteLine("Customer ID: {0} \r\nStreet: {1} "
            + "\r\nCity: {2} \r\nState: {3} \r\nZip Code: {4} \r\nCountry: {5}", 
            item.CustomerID, item.Address, item.City, item.Region, 
            item.PostalCode, item.Country);
    }

    // Save changes to the data service.
    context.SaveChanges();
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred during query execution.", ex);
}

다음 예제에서는 반환된 Customers 엔터티를 새로운 CustomerAddressNonEntity 형식으로 프로젝션하는 LINQ 쿼리를 보여 줍니다. 이 형식에는 주소 관련 속성만 포함되고 ID 속성이 포함되지 않습니다. 이 CustomerAddressNonEntity 클래스는 클라이언트에서 정의되며 엔터티 형식으로 특성이 지정되지 않습니다.

' Create the DataServiceContext using the service URI.
Dim context = New NorthwindEntities(svcUri)

' Define an anonymous LINQ query that projects the Customers type into 
' a CustomerAddress type that contains only address properties.
Dim query = From c In context.Customers _
                Where c.Country = "Germany" _
                Select New CustomerAddressNonEntity With _
                {.CompanyName = c.CompanyName, _
                    .Address = c.Address, _
                    .City = c.City, _
                    .Region = c.Region, _
                    .PostalCode = c.PostalCode, _
                    .Country = c.Country}

Try
    ' Enumerate over the query result, which is executed implicitly.
    For Each item In query
        item.Address += "Street"

        Console.WriteLine("Company name: {0} \nStreet: {1} " _
            & "\nCity: {2} \nState: {3} \nZip Code: {4} \nCountry: {5}", _
            item.CompanyName, item.Address, item.City, item.Region, _
            item.PostalCode, item.Country)
    Next
Catch ex As DataServiceQueryException
    Throw New ApplicationException( _
            "An error occurred during query execution.", ex)
End Try

// Create the DataServiceContext using the service URI.
NorthwindEntities context = new NorthwindEntities(svcUri);

// Define an anonymous LINQ query that projects the Customers type into 
// a CustomerAddress type that contains only address properties.
var query = from c in context.Customers
            where c.Country == "Germany"
            select new CustomerAddressNonEntity
            {
                CompanyName = c.CompanyName, 
                Address = c.Address,
                City = c.City, 
                Region = c.Region,
                PostalCode = c.PostalCode, 
                Country = c.Country
            };

try
{
    // Enumerate over the query result, which is executed implicitly.
    foreach (var item in query)
    {
        item.Address += "Street";

        Console.WriteLine("Company name: {0} \nStreet: {1} "
            + "\nCity: {2} \nState: {3} \nZip Code: {4} \nCountry: {5}",
            item.CompanyName, item.Address, item.City, item.Region,
            item.PostalCode, item.Country);
    }     
}
catch (DataServiceQueryException ex)
{
    throw new ApplicationException(
        "An error occurred during query execution.", ex);
}

다음 예제에서는 이전 예제에서 사용된 CustomerAddress CustomerAddressNonEntity 형식의 정의를 보여 줍니다.

<DataServiceKey("CustomerID")> _
Partial Public Class CustomerAddress
    Private _customerID As String
    Private _address As String
    Private _city As String
    Private _region As String
    Private _postalCode As String
    Private _country As String

    Public Property CustomerID() As String
        Get
            Return Me._customerID
        End Get
        Set(ByVal value As String)
            Me._customerID = Value
        End Set
    End Property
    Public Property Address() As String
        Get
            Return Me._address
        End Get
        Set(ByVal value As String)
            Me._address = Value
        End Set
    End Property
    Public Property City() As String
        Get
            Return Me._city
        End Get
        Set(ByVal value As String)
            Me._city = Value
        End Set
    End Property
    Public Property Region() As String
        Get
            Return Me._region
        End Get
        Set(ByVal value As String)
            Me._region = Value
        End Set
    End Property
    Public Property PostalCode() As String
        Get
            Return Me._postalCode
        End Get
        Set(ByVal value As String)
            Me._postalCode = Value
        End Set
    End Property
    Public Property Country() As String
        Get
            Return Me._country
        End Get
        Set(ByVal value As String)
            Me._country = value
        End Set
    End Property
End Class
Public Class CustomerAddressNonEntity
    Private _companyName As String
    Private _address As String
    Private _city As String
    Private _region As String
    Private _postalCode As String
    Private _country As String

    Public Property CompanyName() As String
        Get
            Return Me._companyName
        End Get
        Set(ByVal value As String)
            Me._companyName = value
        End Set
    End Property
    Public Property Address() As String
        Get
            Return Me._address
        End Get
        Set(ByVal value As String)
            Me._address = Value
        End Set
    End Property
    Public Property City() As String
        Get
            Return Me._city
        End Get
        Set(ByVal value As String)
            Me._city = Value
        End Set
    End Property
    Public Property Region() As String
        Get
            Return Me._region
        End Get
        Set(ByVal value As String)
            Me._region = Value
        End Set
    End Property
    Public Property PostalCode() As String
        Get
            Return Me._postalCode
        End Get
        Set(ByVal value As String)
            Me._postalCode = Value
        End Set
    End Property
    Public Property Country() As String
        Get
            Return Me._country
        End Get
        Set(ByVal value As String)
            Me._country = value
        End Set
    End Property
End Class

[DataServiceKey("CustomerID")]
public partial class CustomerAddress
{
    private string _customerID;
    private string _address;
    private string _city;
    private string _region;
    private string _postalCode;
    private string _country;

    public string CustomerID
    {
        get
        {
            return this._customerID;
        }

        set
        {
            this._customerID = value;
        }
    }
    public string Address
    {
        get
        {
            return this._address;
        }
        set
        {
            this._address = value;
        }
    }
    public string City
    {
        get
        {
            return this._city;
        }
        set
        {
            this._city = value;
        }
    }
    public string Region
    {
        get
        {
            return this._region;
        }
        set
        {
            this._region = value;
        }
    }
    public string PostalCode
    {
        get
        {
            return this._postalCode;
        }
        set
        {
            this._postalCode = value;
        }
    }
    public string Country
    {
        get
        {
            return this._country;
        }
        set
        {
            this._country = value;
        }
    }
}

public class CustomerAddressNonEntity
{
    private string _companyName;
    private string _address;
    private string _city;
    private string _region;
    private string _postalCode;
    private string _country;

    public string CompanyName
    {
        get
        {
            return this._companyName;
        }
        set
        {
            this._companyName = value;
        }
    }
    public string Address
    {
        get
        {
            return this._address;
        }
        set
        {
            this._address = value;
        }
    }
    public string City
    {
        get
        {
            return this._city;
        }
        set
        {
            this._city = value;
        }
    }
    public string Region
    {
        get
        {
            return this._region;
        }
        set
        {
            this._region = value;
        }
    }
    public string PostalCode
    {
        get
        {
            return this._postalCode;
        }
        set
        {
            this._postalCode = value;
        }
    }
    public string Country
    {
        get
        {
            return this._country;
        }
        set
        {
            this._country = value;
        }
    }
}