Tài liệu Creating a Class That Participates in an Automatic Transaction ppt

[ Team LiB ]Recipe 6.1 Creating a Class That Participates in an Automatic Transaction Problem You need to create a .NET class that participates in automatic transactions.. • Objects p

[ Team LiB ]

Recipe 6.1 Creating a Class That Participates in an Automatic Transaction

Problem

You need to create a NET class that participates in automatic transactions

Solution

Use the appropriate custom attributes from the System.EnterpriseServices namespace

The sample contains a component that participates in automatic transactions The

component has a single method, TranTest( ) , that instructs the transaction to succeed or

fail based on an argument success

The sample also contains code that instantiates the component that participates in the

automatic transaction A checkbox on the form is used to specify the success parameter

when the TranTest( ) method is called

The C# code is shown in Examples Example 6-1 and Example 6-2

Example 6-1 ServicedComponentCS Project File: SC0601.cs

// Namespaces, variables, and constants

using System.EnterpriseServices;

using System.Runtime.CompilerServices;

using System.Reflection;

//

namespace AdoDotNetCookbookCS.ServicedComponentCS

{

[Transaction(TransactionOption.Required)]

public class SC0601 : ServicedComponent

{

[AutoComplete]

public void TranTest(bool success)

{

// Do some work

if(success)

{

// don't need the next line since AutoComplete

// ContextUtil.SetComplete( );

}

else

{

// Vote to abort

ContextUtil.SetAbort( );

// Raise an exception

throw new System.Exception(

"Error in Serviced Component 0601 " +

"Transaction aborted.");

}

}

}

}

Example 6-2 File: AutoTransactionForm.cs

// Namespaces, variables, and constants

using System;

using System.Windows.Forms;

using AdoDotNetCookbookCS.ServicedComponentCS;

//

SC0601 sc = new SC0601( );

try

{

sc.TranTest(transactionSucceedCheckBox.Checked);

MessageBox.Show("Transaction successful.", "Automatic Transactions",

MessageBoxButtons.OK, MessageBoxIcon.Information);

}

catch(Exception ex)

{

MessageBox.Show(ex.Message, "Automatic Transactions",

MessageBoxButtons.OK, MessageBoxIcon.Error);

}

Discussion

The NET Common Language Runtime (CLR) supports both manual and automatic

transaction models The automatic distributed transaction model supported by the NET CLR is the same as that supported by Microsoft Transaction Server (MTS) and COM+ The NET Framework provides support for transactional components through the

EnterpriseServices namespace that provides NET objects with access to COM+ services There are two key benefits to automatic transactions:

• They support distributed transactions that span multiple remote databases and multiple resource managers

• Objects participating in automatic transactions do not need to anticipate how they might be used within a transaction A client can perform different tasks with multiple objects, all in the context of a single transaction, without the participating objects being aware of the transaction

The main drawback is:

• Additional overhead because of the interaction with the Distributed Transaction Coordinator (DTC) and the resulting reduction in performance

During the lifetime of an automatic transaction, the objects participating in it can vote to either commit the transaction they are participating in by calling the static SetComplete( ) method of the ContextUtil class or to abort the transaction by calling the static SetAbort( ) method of the ContextUtil class In the absence of an explicit vote, the default is to commit the transaction The transaction is committed once it completes if none of the participating objects have voted to abort

Alternatively, you can apply the AutoCompleteAttribute attribute to a transactional method This attribute instructs NET to vote to commit the transaction, provided no exceptions are encountered in the method If an unhandled exception is thrown, the transaction is automatically rolled back

The NET Framework classes must be prepared before they can participate in an

automatic transaction Once an object is marked to participate in a transaction, it will automatically execute within a transaction The object's transactional behavior is

controlled by the value of the transaction attribute for the NET class, ASP.NET page, or XML web service method using the object This allows the instantiated object to be configured programmatically to participate automatically in an existing transaction, to start a new transaction, or to not participate in a transaction The following steps prepare

a class to participate in an automatic transaction:

1 Derive the class from the ServicedComponent class in the

System.EnterprisesServices namespace

2 Apply the declarative TransactionAttribute to the class and specify the transaction

behavior, timeout, and isolation level This is a value from the TransactionOption enumeration described in Table 6-1

Table 6-1 TransactionOption Enumeration Value Description

Disabled

Automatic transactions do not control the object:

[Transaction(TransactionOption.Disabled)]

NotSupported

The object does not run in the scope of transactions:

[Transaction(TransactionOption.NotSupported)]

Supported

The object runs in context of an existing transaction, if one exists The object runs without a transaction if one does not exist

[Transaction(TransactionOption.Supported)]

Required

The object requires a transaction and runs in context of an existing transaction, if one exists The object starts a transaction if one does not exist

[Transaction(TransactionOption.Required)]

RequiresNew

The object requires a transaction A new transaction is started for each request

[Transaction(TransactionOption.RequiresNew)]

3 Optionally annotate methods with the AutoComplete attribute so that the methods

do not have to explicitly vote for a transaction outcome

4 Sign the assembly with a strong name Use the sn.exe utility to create a key pair

using the following syntax:

sn -k MyApp.snk

Add the AssemblyKeyFileAttribute or AssemblyKeyNameAttribute assembly

attribute to specify the file containing the key pair The following code is used in the solution to sign the assembly:

[assembly: AssemblyDelaySign(false)]

[assembly: AssemblyKeyFile(

@"C:\ADOCookbookCS\ServicedComponentCS\" +

"AdoDotNetCookbookCSServicedComponent.snk")]

[assembly: AssemblyKeyName("AdoDotNetCookbookCSServicedComponent")]

5 Register the assembly containing the class with the COM+ catalog by executing

the NET Services Registration Tool (regsvcs.exe) with the following syntax:

regsvcs /appname:MyApp MyAssembly.dll

This step isn't strictly required If a client calling the class is managed by the CLR, the registration will be performed automatically

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