Serialisasi di LINQ to SQL

  • Artikel

Artikel ini menjelaskan kemampuan serialisasi LINQ to SQL. Paragraf berikut memberikan informasi tentang cara menambahkan serialisasi selama pembuatan kode pada waktu desain dan perilaku serialisasi run-time dari kelas LINQ to SQL.

Anda dapat menambahkan kode serialisasi pada waktu desain dengan salah satu metode berikut:

  • Di Object Relational Designer, ubah properti Mode Serialisasi menjadi Searah.

  • Pada baris perintah SQLMetal, tambahkan opsi /serialisasi. Untuk informasi selengkapnya, lihat SqlMetal.exe (Alat Pembuatan Kode).

Gambaran Umum

Kode yang dihasilkan oleh LINQ to SQL menyediakan kemampuan pemuatan yang ditangguhkan secara default. Pemuatan yang ditangguhkan sangat nyaman di tingkat menengah untuk pemuatan data yang transparan sesuai permintaan. Namun, ini bermasalah untuk serialisasi, karena serializer memicu pemuatan yang ditangguhkan apakah pemuatan yang ditangguhkan dimaksudkan atau tidak. Akibatnya, ketika objek diserialisasikan, penutupan transitifnya di bawah semua referensi yang ditangguhkan keluar diserialisasikan.

Fitur serialisasi LINQ to SQL mengatasi masalah ini, terutama melalui dua mekanisme:

Definisi

  • Serializer DataContract: Serializer default yang digunakan oleh komponen Windows Communication Framework (WCF) dari .NET Framework 3.0 atau versi yang lebih baru.

  • Serialisasi searah: Versi serial dari kelas yang hanya berisi properti asosiasi satu arah (untuk menghindari siklus). Dengan konvensi, properti di sisi induk dari hubungan kunci asing primer ditandai untuk serialisasi. Sisi lain dalam asosiasi dua arah tidak diserialisasikan.

    Serialisasi searah adalah satu-satunya jenis serialisasi yang didukung oleh LINQ to SQL.

Contoh Kode

Kode berikut menggunakan kelas Customer dan Order tradisional dari database sampel Northwind, dan menunjukkan bagaimana kelas ini didekorasi dengan atribut serialisasi.

// 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

Untuk kelas Order dalam contoh berikut, hanya properti asosiasi terbalik yang sesuai dengan kelas Customer yang ditampilkan untuk singkatnya. Ini tidak memiliki atribut DataMemberAttribute untuk menghindari siklus.

// 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

Cara Membuat Serialisasi Entitas

Anda dapat membuat serial entitas dalam kode yang ditunjukkan di bagian sebelumnya sebagai berikut;

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()

Hubungan Rekursif Mandiri

Hubungan Rekursif mandiri mengikuti pola yang sama. Properti asosiasi yang sesuai dengan kunci asing tidak memiliki atribut DataMemberAttribute, sedangkan properti induk memilikinya.

Pertimbangkan kelas berikut yang memiliki dua hubungan rekursif mandiri: Employee.Manager/Reports dan 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)

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