Attach(TEntity) Method

In This Topic

Attaches a disconnected or "detached" entity to a new DataContext when original values are required for optimistic concurrency checks.

Syntax

Visual Basic
C#

'Declaration
 
Public Overloads Sub Attach( _
   ByVal entity As TEntity _
)

public void Attach( 
   TEntity entity
)

Parameters

entity: The original values of the entity to be attached.

Remarks

Use the Attach methods with entities that have been created in one DataContext, and serialized to a client, and then deserialized back with the intention to perform an update or delete operation. Because the new DataContext has no way of tracking what the original values were for a disconnected entity, the client is responsible for supplying those values. In this version of Attach, the entity is assumed to be in its original value state. After calling this method, you can then update its fields, for example with additional data sent from the client. When a new entity is attached, deferred loaders for any child collections (for example, EntitySet collections of entities from associated tables) are initialized. When SubmitChanges is called, members of the child collections are put into an Unmodified state. To update members of a child collection, you must explicitly call Attach and specify that entity.

Do not try to Attach an entity that has not been detached through serialization. Entities that have not been serialized still maintain associations with deferred loaders that can cause unexpected results if the entity becomes tracked by a second data context.

Example

csharp

using (Northwnd db2 = new Northwnd(@"c:\northwnd.mdf"))
{
Customer Cust_File = new Customer();
string xmlFile = "";

    // Get the original object from the deserializer.
Customer c = SerializeHelper.Deserialize
        (xmlFile, Cust_File);

    // Attach it to context as original value
    db2.Customers.Attach(c);

    // Perform updates
    c.Phone = "425-123-4567";
    c.CompanyName = "Microsoft";

    // SubmitChanges()sets the phoneNumber and CompanyName of
    // customer with customerID=Cust. to "425-123-4567" and
    // "Microsoft" respectively.
    db2.SubmitChanges();  
}

Visual Basic

Using db = New Northwnd("...")
Dim Cust_File As New Customer()
Dim xmlFile As String = ""

    'Get the original object from the deserializer.

Dim c As Customer = SerializeHelper.Deserialize(Of Customer)(xmlFile, Cust_File)

    'Attach it to context as original value
    db.Customers.Attach(c)

    ' Perform updates
c.Phone = "425-123-4567"
c.CompanyName = "Microsoft"

    ' SubmitChanges() sets the phoneNumber and CompanyName of
    ' customer with customerID=Cust. to "425-123-4567" and
    ' "Microsoft" respectively.
    db.SubmitChanges()
End Using

Requirements

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

Table<TEntity> Class
Table<TEntity> Members
Overload List

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