Hướng dẫn học Microsoft SQL Server 2008 part 80 pps

FIGURE 33-1The Configure Data Synchronization dialog Once the connections to the server and the client have been created, tables can now be selected.. For example, change the Title for E

Sync Framework example

The best way to understand the Microsoft Sync Framework is to see it in action So before we dive into

any technical mumbo jumbo (I’m starting a new trend; ‘‘mumbo jumbo’’ is the new technical term for

really cool technical stuff), let’s dive right into an example

If you have not installed synchronization services as part of your SQL Server 2008 installation, then

rerun setup (it is an optional feature at the bottom of the Shared Features section), or download the

appropriate Sync Framework Version 2.0 can be found atwww.microsoft.com/downloads/

details.aspx?FamilyId=109DB36E-CDD0-4514-9FB5-B77D9CEA37F6&displaylang=en

This file is a zip file that contains, and installs, the following:

■ Microsoft Sync Framework Runtime v2.0

■ Microsoft Sync Framework SDK v2.0

■ Microsoft Sync Framework Services v2.0

■ Microsoft Sync Framework Services for ADO.NET v3.0 This example also assumes that you have the SQL ServerAdventureWorksdatabases installed These

databases are installed as part of the Microsoft SQL Server installation They are not installed by default,

so if you do not have them, rerun the SQL Server installation and select the Sample Databases feature

Once everything has been installed, start Visual Studio 2008 and create a new Windows Forms

appli-cation It does not matter if you create a VB.NET or C# project, but this example will be using C# On

the New Project dialog, make sure that NET Framework 3.5 is selected This example names the project

‘‘SyncFrameworkDemo,’’ but feel free to name the project whatever suits you

Once the project has been created, the first thing that needs to be done is to add a local data cache

Right-click on the project (it will be called SyncFrameworkDemo) in Solution Explorer and select Add

➪ New Item from the context menu This will open the Add New Item dialog

In the Add New Item dialog, select the Data category tab, and then select the Local Database Cache

tem-plate Name the data cache ‘‘DataCache’’ and click Add

Clicking Add will open the Configuration Data Synchronization dialog This dialog serves several

purposes As it states near the top of the dialog, this is where a connection to a remote database is either

created or selected, and the client connection is created The client connection is the local database

where cached tables are used for synchronization

This dialog is also where the tables are selected to be included in the synchronization and cached

locally If any connections have been previously created, they can be selected in the Server connection

drop-down Otherwise, click the New button next to Server connection, which enables you to define a

connection to the remote database

You can also click the New button next to Client connection to define the connection to the client data

cache Expand the Advanced section to view advanced configuration items, such as synchronization

transactions For this example, no changes will be made to these items

Once connections have been defined, this dialog should look like Figure 33-1

FIGURE 33-1

The Configure Data Synchronization dialog

Once the connections to the server and the client have been created, tables can now be selected To do

this, click the Add button below the Cached Tables list This will open the dialog shown in Figure 33-2

The Configure Tables dialog enables you to select the tables to be included in the client-side cache

Think about this for a minute When dealing with Sync Services, you need to consider where this

functionality will more than likely be used In a real-world scenario, you would probably see Sync

Services used in applications that run on laptops, but you might also see Sync Services running on

tablets or PDAs — devices that really don’t have a lot of storage capabilities For this reason, you don’t

want to select every single table You want to select only the tables that are practical for the application

In this example I have connected to theAdventureWorksdatabase, which has just over 70 tables For

this example, only theHumanResources.Employeetable will be used Notice that prior to selecting

any tables, the information on the right is grayed out As you select a table, the options on the right are

enabled, providing the capability to define synchronization properties per table

■ Data to download: ‘‘New and incremental changes after first synchronization’’ retrieves records

from the server that have been modified since the last time data was synchronized The entire

table is downloaded the first time synchronization is called ‘‘Entire table each time’’ drops the

local table and replaces it with the version on the server

■ Compare updates using: This option enables you to select the column name in the selected table that is used to track when the last update of a record was made Any column in the table that is defined as adatetimeortimestampdata type will appear in this list You can also choose to let a new column calledLastEditDatebe created in the table

■ Compare inserts using: Enables you to select the column name in the selected table that

is used to track when new records are added to the table Any column in the table that is defined as adatetimeortimestampdata type will appear in this list You can also choose

to let a new column called CreationDate be created in the table

■ Move deleted items to: Enables you to pick the table on the server that will be used to store deleted records If a table namedtablename_Deletedortablename_Tombstonealready exists on the server, that table will be used for the deleted items; otherwise, a table named

tablename_Tombstonewill be created

FIGURE 33-2

The Configure Tables for Offline Use dialog box is where you select tables

After you have selected the tables you want to cache, click OK This will bring you back to the

Config-uration Data Synchronization dialog with the tables you selected listed under the Cached Tables section

Click OK on this dialog

A small dialog will appear informing you that it needs to update the server, giving you the option to

save SQL scripts to be used later if needed By default, both of these options are selected Click OK on

this dialog

The wizard will then create the local database cache (.sdf), create the selected tables inside that database,

and then copy over the records for each of those tables Once all of the data is copied over, the next

step in the wizard will appear, asking you which of the selected tables in the database cache should be

included in the dataset, as shown in Figure 33-3

FIGURE 33-3

Use this dialog box to choose which objects sets you want included in your dataset

Select all of the tables in this dialog and click Finish The dataset is then created with the selected

tables

At this point, your Solution Explorer should look like Figure 33-4, containing the client database cache,

the appropriate references, SQL scripts, and a blank form called Form1 From here it is time to start

writing code to synchronize the local cache with the main database and vice versa Luckily, Microsoft

makes this really easy — very little code is required to get synchronization working

In the Visual Studio IDE, make sure that the Data Sources Explorer bar is displayed If it is not, then

select Show Data Sources from the Data menu The Data Sources Explorer bar will open on the left side

of the IDE by default

Open form1 in design view; and in the Data Sources Explorer (see Figure 33-5), select theHuman

_Resources_Employeetable, ensuring that the DataGridView option is selected from the drop-down

menu Drag the Employee table onto the form

FIGURE 33-4

Check your Solution Explorer for the client database cache, the appropriate references, SQL scripts,

and a blank form

FIGURE 33-5

The Data Sources Explorer lets you select the DataGridView

Here is where it gets cool Visual Studio automatically creates the data grid and navigation controls for

you Not only that, it also creates a ton of the code behind the form as well, such as saving and

loading of the data How awesome is that! Visual Studio will automatically place the navigation bar at

the top of the form, and randomly place the grid below that Select the grid on the form, and in the

properties of that grid set theDockproperty toFill.This will ensure that the grid fills the rest of

the form and even expand with the form as it is resized Notice that the navigation bar has most of the

button functionality needed to work with the grid, such as add, delete, and save

As the form sits now, it really can’t do any synchronization It can and will load the data and save the

data back to the cache if any changes are made and the Save button on the navigation bar is clicked

Go ahead and run the application as is Notice that the data is loaded when the form loads While this

is nice, it can also be a nuisance For example, theSalesOrderHeadertable contains roughly 31,500

records That might take a moment to load However, what if there were 100,000 records or more?

From a user-experience standpoint, you really don’t want the application, or any form for that matter, to

take a long time to display while it loads a ton of data

The next steps, therefore, are going to implement synchronization logic and change when the loading

of the data takes place The really neat part about this is that it takes only a few lines of code to do all

of this Sweet

The first thing that needs to be done is to add a couple of buttons to the navigation bar Again, this is

really easy Simply click on the navigation bar next to the Save button and a new object placeholder will

appear with a drop-down arrow When the arrow is selected, a list of objects appears that can be added

to the navigation bar, as shown in Figure 33-6 For this example, select the top option, Button This will

be the button that loads the data when clicked Add another button for the synchronization

FIGURE 33-6

A list of objects can be added to the navigation bar

To make things easy, rename the first button from toolStripButton1 to ‘‘btnLoadData’’ and set itsText

property toLoad Data.Rename the second button to ‘‘btnSync’’ and set itsTextproperty toSync

Data.Setting theTextproperty will display the text when you hover the mouse over each button

Double-click the first button, which will open the code behind the form and create theClick()

event for this button This event will not contain code, but the code we do want is in the load event

of the form Therefore, find the Form1_Load event and copy and paste the following line of code from

the form load event to the btnLoadData click event:

this.humanResources_EmployeeTableAdapter.Fill(

this.adventureWorksDataSet.HumanResources_Employee);

This line of code was placed in the load event of the form by Visual Studio when the controls were

placed on the form Moving this line of code from the load event to the click event of the button will

speed up the loading of the form

Go ahead and test what you currently have by saving all the changes and running the project From

the Debug menu, select Start Debugging When the form opens, it will show an empty grid Click the

Load Data button After a couple of seconds the grid should populate with all of the employee records

Remember that the data is coming from the local cache (the sdf)

Close the form The next step is to add the sync functionality Once again, this is easy Referring to

Figure 33-1, notice that the bottom right-hand corner of that form contains a link named Show Code

Example That is exactly what is needed for this example, so in Visual Studio open the Solution Explorer

and double-clickDataCache.sync This will open the Configure Data Synchronization dialog shown in

Figure 33-1 Click the Show Code Example link The Code Example dialog will be displayed, showing

a fragment of code that can actually be used Simply click the Copy Code to Clipboard button This

copies the displayed code to the Windows clipboard Close the Code Example dialog, and then close the

Configure Data Synchronization dialog

With the synchronization code on the clipboard, go back to the project form and double-click on the

Data Sync button, which will open the code behind the form and create theClick()event for this

button In theClick()event for the DataSync button, paste the code from the Windows clipboard

into this event TheClick()event should now look like the following:

private void SyncData_Click(object sender, EventArgs e) {

// Call SyncAgent.Synchronize() to initiate the synchronization process

// Synchronization only updates the local database, not your // project’s data source

DataCacheSyncAgent syncAgent = new DataCacheSyncAgent();

Microsoft.Synchronization.Data.SyncStatistics syncStats = syncAgent.Synchronize();

// TODO: Reload your project data source from the local database (for example, call the TableAdapter.Fill method)

}

Not quite done, because the code that does the actual merge to the local cache needs to be added Right

below theTODOcomment in the code, add the following line:

this.adventureWorksDataSet.Merge(

humanResources_EmployeeTableAdapter.GetData());

With that, your first sync example is done and ready to test Run the project again and click the Load

Data button With the data loaded, keep the form open and open SQL Server Management Studio

and the data server where the source data resides Open theAdventureWorksdatabase, and in the

Tables node, right-click on theHumanResources.Employeetable and select Open Table from the

context menu

To test synchronization, within SSMS (SQL Server Management Studio) change the Title of one of the

employees For example, change the Title for EmployeeID 2 from ‘‘Marketing Assistant’’ to ‘‘Marketing

Director.’’

Now go back to the project form and click the Sync Data button The title ‘‘Marketing Assistant’’ in the

local cache will also change to ‘‘Marketing Director.’’ Try to sync in the other direction by changing

some data on the form Make sure you click the Save button so that the data is saved back to the cache

Now click the Sync Data button

Requery the source data and you will see that it has not been changed This is because, by default,

syn-chronization is only one direction; from the source to the client To fix this and set synsyn-chronization to

bi-directional is a really easy change In the Solution Explorer, right-click on theDataCache.syncand

select View Code from the context menu What you will see is the following:

public partial class DataCacheSyncAgent {

partial void OnInitialized(){

} }

Within theOnInitialized()method, add the following statement:

HumanResources_Employee.SyncDirection =

Microsoft.Synchronization.Data.SyncDirection.Bidirectional;

This statement simply tells the synchronization agent to sync both ways, not just up or down Now try

the change again Start the application, load the data, make a change on the client, save the changes,

and then click the Sync Data button Then, go back to the source data and verify that the data on the

server reflects the change or changes made on the client

One last note for this example: Bi-directional sync can be tricky What if both the client and the server

update the same record? Who wins, and how does sync handle this?

Luckily, synchronization provides a way to take care of this Any and all conflicts automatically

raise anApplyChangesFailedevent This can be accomplished by adding a method to the

SyncProviderpartial class In the same class to which you added code earlier, add the following

below theOnInitializedmethod:

void DataCache_ApplyChangeFailed(object sender,

Microsoft.Synchronization.Data.ApplyChangeFailedEventArgs e)

{

DataTable cc = e.Conflict.ClientChange;

DataTable sc = e.Conflict.ServerChange;

if ((System.DateTime)(cc.Rows[0]["ModifiedDate"]) >=

(System.DateTime)(sc.Rows[0]["ModifiedDate"]))

{

e.Action = Microsoft.Synchronization.Data.ApplyAction

.RetryWithForceWrite;

}

}

In this method, theModifiedDateon the server is compared to theModifiedDateon the client

If the clientModifiedDateis later than theModifiedDateon the server, then the server record is

forcefully updated with that of the client

To test this, run the project and modify a record on the client and save it Next, modify the same record

on the server Click the Sync Data button Because the server record was modified later, this will win

the synchronization battle Had the client date been later than the server date, the client would have

won the synchronization battle and updated the server

This example is a very simple demonstration of how the Sync Framework and synchronization works

Obviously, additional business logic can be placed in many areas to provide additional sync capabilities

or to satisfy business rules, but it should give you a good idea of how powerful and flexible the Sync

Framework is and how easy it is to use

Keep in mind that SQL Server 2008 introduces change tracking This is a lightweight and very thin

solution that provides a very robust change tracking mechanism for applications While this chapter

does not cover SQL Server change tracking specifically, it would be worth your while to understand

change tracking and how it can be used in your environment

So with that introduction, it is time to get into the nitty-gritty We begin with a brief overview of the

Sync Framework before diving into some of its great technologies

Sync Framework overview

The Microsoft Sync Framework is a very broad and wide-ranging synchronization platform that enables

developers to architect and develop applications targeted toward offline and collaboration scenarios It

would be quite narrow-minded to think that this technology can be used only in applications, however,

because included in the list of uses for offline and collaboration scenarios are services and mobile

devices, and each of these is a prime target for synchronization technology The Sync Framework allows

for the building of systems that integrate any application to any data store by using any protocol over

any network How sweet is that!

Also data is not limited to information stored in databases Data also comes in the form of files The

Microsoft Sync Framework enables business applications to share documents to guarantee that all team

members receive the necessary data

The Sync Framework contains the following technologies:

■ Sync Framework core components: Used to create sync providers for any type of data store

■ Microsoft Sync Services for ADO.NET: Used to sync databases for offline and joint scenarios

■ Metadata Storage Services: Used to store sync metadata

■ Sync Services for File Systems: Used to sync file system files and folders

■ Sync Services for FeedSync: Used to sync RSS and Atom feeds with a local data store

At least 25 pages could be written on each one of these technologies, but due to space constraints

Metadata Storage Services, Sync Services for File Systems, and Sync Services for FeedSync will not

be covered in this chapter Plenty of information, though, can be found on Microsoft’s MSDN site at

http://msdn.microsoft.com/en-us/library/cc307159.aspx

The rest of this chapter provides an overview of the Sync Framework core components, a discussion of

the Sync architecture and synchronization fundamentals, as well as a good discussion of Sync Services

for ADO.NET 2.0

Sync architecture

The Microsoft Sync Framework architecture enables the flow of data between many devices and services

by using a set of building blocks that incorporate all of the synchronization functionality, such as the

data store and transfer systems These building blocks are the essential components that make up the

synchronization runtime, metadata services, and synchronization providers

During synchronization, the sync runtime drives and controls synchronization between the providers It

is the job of the metadata services to process and store metadata that is used by the providers

For example, Figure 33-7 illustrates a simple high-level architecture of the Microsoft Sync Framework in

which synchronization is attained by exposing a provider interface from a data store to a synchronization

object

This example is quite simple, in that it is illustrating a synchronization between a single data store and a

controlling application such as a mobile device and a Microsoft SQL Server database

FIGURE 33-7

A simple high-level architecture

Master Sync

Application Sync Session Sync Provider

Data Store

FIGURE 33-8

An architecture of multiple data stores synchronizing with a single controlling application, with each

data store using its own synchronization provider

Master Sync

Application Sync Session

Sync Provider

Data Store

Sync Provider

Data Store

However, the Sync Framework is much more flexible and interoperable than that For example, the

illustration shown in Figure 33-8 shows multiple data stores synchronizing with a single controlling

application, with each data store using its own synchronization provider This is important because the

two data stores could be two completely different and unique types of data stores

In both scenarios, the sync session connects to both sync providers It then makes appropriate API calls

to determine what changes have been made and what changes need to be applied Again, this

informa-tion is supplied by the metadata services

The sync runtime has the primary responsibility of driving and managing synchronization This includes

starting and hosting the sync process, and disposing of the session when synchronization is complete

The runtime also controls all communication with the client application, including status, conflicts,

and any errors The runtime initiates and begins synchronization for the client application by making

requests through the sync session to the sync providers

The role of the metadata service is to manage synchronization metadata The metadata service has the

sole responsibility of understanding the details of the metadata, thereby freeing the application and

provider from needing to understand items such as the structure of the data By assisting the application

in this way, it allows for maximum flexibility when designing applications It also provides improved

synchronization performance by enabling the other components to focus on what they excel at

The sync provider is the main integration point into the Sync Framework, as it contains a layer that

shields the runtime from the complexities of the data store In terms of a provider, the sync provider

is the component that enables synchronization between data stores The great thing about the Sync