LINQ to SQL 中的序列化
本文說明 LINQ to SQL 的序列化功能。 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，將序列化模式屬性變更為單向。
在 SQLMetal 命令列，加入 /serialization 選項。 如需詳細資訊，請參閱 SqlMetal.exe (程式碼產生工具)。
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：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：只含有單向關聯屬性 (可避免循環) 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()]
public partial class Customer : INotifyPropertyChanging, INotifyPropertyChanged
{
' The class is decorated with the DataContract attribute.
<Table(Name:="dbo.Customers"), _
DataContract()> _
Partial Public Class Customer
Implements System.ComponentModel.INotifyPropertyChanging, System.ComponentModel.INotifyPropertyChanged
// 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();
}
}
}
' 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
// 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);
}
}
' 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
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 DataMemberAttribute 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()]
public partial class Order : INotifyPropertyChanging, INotifyPropertyChanged
' 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
// 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
' 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
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：
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();
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()
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 DataMemberAttribute 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 Employee Manager;
[DataMember(Order = 3)]
public EntitySet<Employee> Reports;
// No DataMember
public Employee Mentor;
[DataMember(Order = 5)]
public EntitySet<Employee> 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)