展示模型

發行項
03/11/2011

WCF RIA Services 可讓您建立用於彙總資料存取層中多個實體資料的資料模型，也就是展示模型。當您不想要向用戶端公開資料存取層的實體時，可以使用此功能。使用展示模型時，可以只變更展示模型而不變更用戶端，以回應資料存取層的變更。此外，也可以設計只彙總那些與用戶端使用者有關之欄位的模式，以簡化用戶端程式碼。本主題將說明如何建立、查詢和更新展示模型，以及當變更已在中介層或資料來源中設定時，如何將值傳回用戶端。

建立展示模型

維持資料完整性所需的資料庫結構可能比用戶端應用程式實體所需的更複雜。您可以將與應用程式有關的欄位併入一個展示模型，以建立簡化此資料結構的展示模型。例如，在 AdventureWorksLT 範例資料庫中，透過 Customer、CustomerAddress 和 Address 資料表擷取客戶與地址資料。

RS_CustomerEntities

在伺服器專案中建立類別並定義可用的屬性，以建立展示模型。定義的屬性會對應至要從實體公開屬性。例如，您可以在伺服器專案中建立下列 CustomerPresentationModel 類別，只顯示要從 Customer、CustomerAddress 和 Address 資料表取得的欄位。

Public Class CustomerPresentationModel
    <Key()> _
    Public Property CustomerID As Integer
    Public Property FirstName As String
    Public Property LastName As String
    Public Property EmailAddress As String
    Public Property Phone As String
    Public Property AddressType As String
    Public Property AddressLine1 As String
    Public Property AddressLine2 As String
    Public Property City As String
    Public Property StateProvince As String
    Public Property PostalCode As String
    Public Property AddressID As Integer
    Public Property AddressModifiedDate As DateTime
    Public Property CustomerModifiedDate As DateTime
End Class

public class CustomerPresentationModel
{
    [Key]
    public int CustomerID { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string EmailAddress { get; set; }
    public string Phone { get; set; }
    public string AddressType { get; set; }
    public string AddressLine1 { get; set; }
    public string AddressLine2 { get; set; }
    public string City { get; set; }
    public string StateProvince { get; set; }
    public string PostalCode { get; set; }
    public int AddressID { get; set; }
    public DateTime AddressModifiedDate { get; set; }
    public DateTime CustomerModifiedDate { get; set; }
}

查詢及修改展示模型中的值

在建立展示模型之後，加入與展示型別互動的網域服務，藉以將展示模型公開給用戶端專案。實體值只會經由這個網域服務公開，並不會經由公開整個實體的網域服務公開。下列範例將示範衍生自 DomainService 類別的網域服務。

[EnableClientAccess()]
public class CustomerDomainService : DomainService
{
    AdventureWorksLT_DataEntities context = new AdventureWorksLT_DataEntities();
}

為擷取資料，要將查詢方法加入至網域服務。在查詢方法中，要從資料存取層的實體擷取相關資料，並設定那些值至展示模型的新執行個體中的對應屬性。從查詢方法中，要傳回展示模型型別的執行個體，或 IQueryable’1，其中泛型型別為 CustomerPresentationModel 型別。下列範例將示範客戶展示模型的查詢方法。

Public Function GetCustomersWithMainOffice() As IQueryable(Of CustomerPresentationModel)
    Return From c In context.Customers
        Join ca In context.CustomerAddresses On c.CustomerID Equals ca.CustomerID
        Join a In context.Addresses On ca.AddressID Equals a.AddressID
        Where ca.AddressType = "Main Office"
               Select New CustomerPresentationModel() With _
               {
                   .CustomerID = c.CustomerID,
                   .FirstName = c.FirstName,
                   .LastName = c.LastName,
                   .EmailAddress = c.EmailAddress,
                   .Phone = c.Phone,
                   .AddressType = ca.AddressType,
                   .AddressLine1 = a.AddressLine1,
                   .AddressLine2 = a.AddressLine2,
                   .City = a.City,
                   .StateProvince = a.StateProvince,
                   .PostalCode = a.PostalCode,
                   .AddressID = a.AddressID,
                   .AddressModifiedDate = a.ModifiedDate,
                   .CustomerModifiedDate = c.ModifiedDate
               }
End Function

public IQueryable<CustomerPresentationModel> GetCustomersWithMainOffice()
{
    return from c in context.Customers
        join ca in context.CustomerAddresses on c.CustomerID equals ca.CustomerID
        join a in context.Addresses on ca.AddressID equals a.AddressID
        where ca.AddressType == "Main Office"
           select new CustomerPresentationModel()
           {
               CustomerID = c.CustomerID,
               FirstName = c.FirstName,
               LastName = c.LastName,
               EmailAddress = c.EmailAddress,
               Phone = c.Phone,
               AddressType = ca.AddressType, 
               AddressLine1 = a.AddressLine1, 
               AddressLine2 = a.AddressLine2,
               City = a.City, 
               StateProvince = a.StateProvince, 
               PostalCode = a.PostalCode,
               AddressID = a.AddressID,
               AddressModifiedDate = a.ModifiedDate,
               CustomerModifiedDate = c.ModifiedDate
           };
}

因為網域服務未公開資料存取層的 (Customer、CustomerAddress 和 Address) 實體，在用戶端專案中並不產生那些型別，而是只產生 CustomerPresentationModel 型別。

為透過展示模型更新資料，要建立更新方法並定義用來將展示模型的值儲存至實體的邏輯。下一節結尾處所列的是更新方法的範例。

將值傳回用戶端

在送出變更之後，您可能會想要將中介層或資料來源中設定的值傳回用戶端。RIA Services 提供 Associate 方法，可將實體的值對應回展示模型。在這個方法中，要提供在送出變更後呼叫的回呼方法。在回呼方法中，要將任何已在中介層修改過的值指派至展示模型。執行這個步驟可確保用戶端處理目前的值。

下列範例將示範如何更新實體中的值，以及如何將修改過的資料對應回展示模型。

<Update()> _
Public Sub UpdateCustomer(ByVal customerPM As CustomerPresentationModel)
    Dim customerEntity As Customer = context.Customers.Where(Function(c) c.CustomerID = customerPM.CustomerID).FirstOrDefault()
    Dim customerAddressEntity As CustomerAddress = context.CustomerAddresses.Where(Function(ca) ca.CustomerID = customerPM.CustomerID And ca.AddressID = customerPM.AddressID).FirstOrDefault()
    Dim addressEntity As Address = context.Addresses.Where(Function(a) a.AddressID = customerPM.AddressID).FirstOrDefault()

    customerEntity.FirstName = customerPM.FirstName
    customerEntity.LastName = customerPM.LastName
    customerEntity.EmailAddress = customerPM.EmailAddress
    customerEntity.Phone = customerPM.Phone
    customerAddressEntity.AddressType = customerPM.AddressType
    addressEntity.AddressLine1 = customerPM.AddressLine1
    addressEntity.AddressLine2 = customerPM.AddressLine2
    addressEntity.City = customerPM.City
    addressEntity.StateProvince = customerPM.StateProvince
    addressEntity.PostalCode = customerPM.PostalCode

    Dim originalValues As CustomerPresentationModel = Me.ChangeSet.GetOriginal(customerPM)

    If (originalValues.FirstName <> customerPM.FirstName Or
            originalValues.LastName <> customerPM.LastName Or
            originalValues.EmailAddress <> customerPM.EmailAddress Or
            originalValues.Phone <> customerPM.Phone) Then
        customerEntity.ModifiedDate = DateTime.Now
    End If

    If (originalValues.AddressLine1 <> customerPM.AddressLine1 Or
            originalValues.AddressLine2 <> customerPM.AddressLine2 Or
            originalValues.City <> customerPM.City Or
            originalValues.StateProvince <> customerPM.StateProvince Or
            originalValues.PostalCode <> customerPM.PostalCode) Then
        addressEntity.ModifiedDate = DateTime.Now
    End If

    context.SaveChanges()

    Me.ChangeSet.Associate(customerPM, customerEntity, AddressOf MapCustomerToCustomerPM)
    Me.ChangeSet.Associate(customerPM, addressEntity, AddressOf MapAddressToCustomerPM)
End Sub

Private Sub MapCustomerToCustomerPM(ByVal customerPM As CustomerPresentationModel, ByVal customerEntity As Customer)
    customerPM.CustomerModifiedDate = customerEntity.ModifiedDate
End Sub

Private Sub MapAddressToCustomerPM(ByVal customerPM As CustomerPresentationModel, ByVal addressEntity As Address)
    customerPM.AddressModifiedDate = addressEntity.ModifiedDate
End Sub

[Update]
public void UpdateCustomer(CustomerPresentationModel customerPM)
{
    Customer customerEntity = context.Customers.Where(c => c.CustomerID == customerPM.CustomerID).FirstOrDefault();
    CustomerAddress customerAddressEntity = context.CustomerAddresses.Where(ca => ca.CustomerID == customerPM.CustomerID && ca.AddressID == customerPM.AddressID).FirstOrDefault();
    Address addressEntity = context.Addresses.Where(a => a.AddressID == customerPM.AddressID).FirstOrDefault();

    customerEntity.FirstName = customerPM.FirstName;
    customerEntity.LastName = customerPM.LastName;
    customerEntity.EmailAddress = customerPM.EmailAddress;
    customerEntity.Phone = customerPM.Phone;
    customerAddressEntity.AddressType = customerPM.AddressType;
    addressEntity.AddressLine1 = customerPM.AddressLine1;
    addressEntity.AddressLine2 = customerPM.AddressLine2;
    addressEntity.City = customerPM.City;
    addressEntity.StateProvince = customerPM.StateProvince;
    addressEntity.PostalCode = customerPM.PostalCode;

    CustomerPresentationModel originalValues = this.ChangeSet.GetOriginal(customerPM);

    if (originalValues.FirstName != customerPM.FirstName ||
        originalValues.LastName != customerPM.LastName ||
        originalValues.EmailAddress != customerPM.EmailAddress ||
        originalValues.Phone != customerPM.Phone)
    {
        customerEntity.ModifiedDate = DateTime.Now;
    }

    if (originalValues.AddressLine1 != customerPM.AddressLine1 ||
        originalValues.AddressLine2 != customerPM.AddressLine2 ||
        originalValues.City != customerPM.City ||
        originalValues.StateProvince != customerPM.StateProvince ||
        originalValues.PostalCode != customerPM.PostalCode)
    {
        addressEntity.ModifiedDate = DateTime.Now;
    }

    context.SaveChanges();

    this.ChangeSet.Associate(customerPM, customerEntity, MapCustomerToCustomerPM);
    this.ChangeSet.Associate(customerPM, addressEntity, MapAddressToCustomerPM);
}

private void MapCustomerToCustomerPM(CustomerPresentationModel customerPM, Customer customerEntity)
{
    customerPM.CustomerModifiedDate = customerEntity.ModifiedDate;
}

private void MapAddressToCustomerPM(CustomerPresentationModel customerPM, Address addressEntity)
{
    customerPM.AddressModifiedDate = addressEntity.ModifiedDate;
}

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展示模型

建立展示模型

查詢及修改展示模型中的值

將值傳回用戶端

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