序列化 (LINQ to SQL)

發行項
08/21/2008

更新： November 2007

本主題描述 LINQ to SQL 序列化 (Serialization) 功能。後續段落會提供有關如何在設計階段的程式碼產生期間加入序列化以及 LINQ to SQL 類別 (Class) 的執行階段序列化行為。

您可以透過下列其中一種方法，在設計階段加入序列化程式碼：

在物件關聯式設計工具中，將 [序列化模式] 屬性變更為 [單向]。
在 SQLMetal 命令列上，加入 /serialization 選項。如需詳細資訊，請參閱程式碼產生工具 (SqlMetal.exe)。

概觀

LINQ to SQL 所產生的程式碼預設會提供延後載入功能。在視需要透明載入資料的中介層中，延後載入非常方便。但是，由於不論是否需要延後載入，序列化程式都會觸發延後載入，所以序列化會有問題。事實上，序列化物件後，在所有傳出延後載入的參考之下的遞移封閉 (Transitive Closure) 也已序列化。

LINQ to SQL 序列化功能會處理這個問題，主要透過下列兩個機制：

用於關閉延後載入的 DataContext 模式 (ObjectTrackingEnabled)。如需詳細資訊，請參閱 DataContext。
程式碼產生參數，用在產生的實體上產生 System.Runtime.Serialization.DataContractAttribute 和 System.Runtime.Serialization.DataMemberAttribute 屬性 (Attribute)。這個方面 (包含序列化之下延後載入類別的行為) 為本主題的主旨。

定義

DataContract 序列化程式 (DataContract Serializer)：由 .NET Framework 3.0 或較新版本的 Windows Communication Framework (WCF) 元件使用的預設序列化程式。
單向序列化 (Unidirectional Serialization)：只含有單向關聯屬性 (Poperty) (可避免循環) 之類別的序列化版本。依照慣例，主索引鍵-外部索引鍵關聯性之父端上的屬性 (Poperty) 會標記為即將序列化。雙向關聯中的另一端則不會序列化。

單向序列化是 LINQ to SQL 唯一支援的序列化類型。

程式碼範例

下列程式碼會使用 Northwind 範例資料庫中的傳統 Customer 和 Order 類別，並且顯示如何使用序列化屬性 (Attribute) 裝飾這些類別。

' The class is decorated with the DataContract attribute.
<Table(Name:="dbo.Customers"),  _
 DataContract()>  _
Partial Public Class Customer
    Implements System.ComponentModel.INotifyPropertyChanging, System.ComponentModel.INotifyPropertyChanged

// The class is decorated with the DataContract attribute.
[Table(Name="dbo.Customers")]
[DataContract()]
public partial class Customer : INotifyPropertyChanging, INotifyPropertyChanged
{

    ' Private fields are not decorated with any attributes,
    ' and are elided.
    Private _CustomerID As String

    ' Public properties are decorated with the DataMember
    ' attribute and the Order property specifying the
    ' serial number. See the Order class later in this topic
    ' for exceptions
    <Column(Storage:="_CustomerID", DbType:="NChar(5) NOT NULL", CanBeNull:=false, IsPrimaryKey:=true),  _
     DataMember(Order:=1)>  _
    Public Property CustomerID() As String
        Get
            Return Me._CustomerID
        End Get
        Set
            If ((Me._CustomerID = value)  _
                        = false) Then
                Me.OnCustomerIDChanging(value)
                Me.SendPropertyChanging
                Me._CustomerID = value
                Me.SendPropertyChanged("CustomerID")
                Me.OnCustomerIDChanged
            End If
        End Set
    End Property

    // Private fields are not decorated with any attributes, and are
    // elided.
    private string _CustomerID;

    // Public properties are decorated with the DataMember
    // attribute and the Order property specifying the serial
    // number. See the Order class later in this topic for
    // exceptions.
    public Customer()
    {
        this.Initialize();
    }
    
    [Column(Storage="_CustomerID", DbType="NChar(5) NOT NULL", CanBeNull=false, IsPrimaryKey=true)]
    [DataMember(Order=1)]
    public string CustomerID
    {
        get
        {
            return this._CustomerID;
        }
        set
        {
            if ((this._CustomerID != value))
            {
                this.OnCustomerIDChanging(value);
                this.SendPropertyChanging();
                this._CustomerID = value;
                this.SendPropertyChanged("CustomerID");
                this.OnCustomerIDChanged();
            }
        }
    }

   ' The following Association property is decorated with
   ' DataMember because it is the parent side of the
   ' relationship. The reverse property in the Order
   ' class does not have a DataMember attribute. This
   ' factor prevents a 'cycle.'
   <Association(Name:="FK_Orders_Customers", Storage:="_Orders", OtherKey:="CustomerID", DeleteRule:="NO ACTION"), _
 DataMember(Order:=13)> _
Public Property Orders() As EntitySet(Of [Order])
       Get
           Return Me._Orders
       End Get
       Set(ByVal value As EntitySet(Of [Order]))
           Me._Orders.Assign(Value)
       End Set
   End Property

    // The following Association property is decorated with
    // DataMember because it is the parent side of the
    // relationship. The reverse property in the Order class
    // does not have a DataMember attribute. This factor
    // prevents a 'cycle.'
    [Association(Name="FK_Orders_Customers", Storage="_Orders", OtherKey="CustomerID", DeleteRule="NO ACTION")]
    [DataMember(Order=13)]
    public EntitySet<Order> Orders
    {
        get
        {
            return this._Orders;
        }
        set
        {
            this._Orders.Assign(value);
        }
    }

至於下列範例中的 Order 類別，只有對應至 Customer 類別的反向關聯屬性 (Property) 會簡短顯示。該類別沒有 DataMember 屬性 (Attribute) 可避免循環。

' The class for the Orders table is also decorated with the
' DataContract attribute.
<Table(Name:="dbo.Orders"),  _
 DataContract()>  _
Partial Public Class [Order]
    Implements System.ComponentModel.INotifyPropertyChanging, System.ComponentModel.INotifyPropertyChanged

// The class for the Orders table is also decorated with the
// DataContract attribute.
[Table(Name="dbo.Orders")]
[DataContract()]
public partial class Order : INotifyPropertyChanging, INotifyPropertyChanged

    ' Private fields for the Orders table are not decorated with
    ' any attributes, and are elided.
    Private _CustomerID As String

    ' Public properties are decorated with the DataMember
    ' attribute.
    ' The reverse Association property on the side of the
    ' foreign key does not have the DataMember attribute.
    <Association(Name:="FK_Orders_Customers", Storage:="_Customer", ThisKey:="CustomerID", IsForeignKey:=true)>  _
    Public Property Customer() As Customer

    // Private fields for the Orders table are not decorated with
    // any attributes, and are elided.
    private int _OrderID;

    // Public properties are decorated with the DataMember
    // attribute.
    // The reverse Association property on the side of the
    // foreign key does not have the DataMember attribute.
    [Association(Name = "FK_Orders_Customers", Storage = "_Customer", ThisKey = "CustomerID", IsForeignKey = true)]
    public Customer Customer

如何將實體序列化

您可以在上一節顯示的程式碼中將實體序列化，如下所示：

Dim db As New Northwnd("...")

Dim cust = (From c In db.Customers _
           Where c.CustomerID = "ALFKI").Single

Dim dcs As New DataContractSerializer(GetType(Customer))

Dim sb As StringBuilder = New StringBuilder()
Dim writer As XmlWriter = XmlWriter.Create(sb)
dcs.WriteObject(writer, cust)
writer.Close()
Dim xml As String = sb.ToString()

Northwnd db = new Northwnd(@"c\northwnd.mdf");

Customer cust = db.Customers.Where(c => c.CustomerID ==
    "ALFKI").Single();

DataContractSerializer dcs = 
    new DataContractSerializer(typeof(Customer));
StringBuilder sb = new StringBuilder();
XmlWriter writer = XmlWriter.Create(sb);
dcs.WriteObject(writer, cust);
writer.Close();
string xml = sb.ToString();

自我遞迴關聯性

自我遞迴關聯性會依循相同的模式。對應至外部索引鍵的關聯屬性 (Property) 沒有 DataMember 屬性 (Attribute)，然而父屬性 (Property) 卻有該屬性 (Attribute)。

請考慮下列具有兩個自我遞迴關聯性的類別：Employee.Manager/Reports 和 Employee.Mentor/Mentees。

' No DataMember attribute
Public Manager As Employee
<DataMember(Order:=3)> _
Public Reports As EntitySet(Of Employee)

' No DataMember attribute
Public Mentor As Employee
<DataMember(Order:=5)> _
Public Mentees As EntitySet(Of Employee)

// No DataMember attribute.
public Employee Manager;
[DataMember(Order = 3)]
public EntitySet<Employee> Reports;

// No DataMember
public Employee Mentor;
[DataMember(Order = 5)]
public EntitySet<Employee> Mentees;

請參閱

共用方式為

序列化 (LINQ to SQL)

概觀

定義

程式碼範例

如何將實體序列化

自我遞迴關聯性

請參閱

工作

參考

其他資源

其他資源