Microsoft SQL Server 2005 Developer’s Guide- P17 doc

The following example shows how to use the RollbackTrans method: Private Sub TransRollBackcn As ADODB.Connection Dim rs As New ADODB.Recordset 'Start a transaction using the existing C

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error handler is fired, enabling you to trap and respond to run-time errors This tight

integration with Visual Basic makes it easy to handle ADO errors The following

ShowError subroutine illustrates how ADO’s error handling can be integrated with

Visual Basic’s On Error function:

Private Sub ShowError(cn As ADODB.Connection)

Dim rs As New ADODB.Recordset

On Error GoTo ErrorHandler

rs.Open "Select * From no_such_table", cn

rs.Close

Exit Sub

ErrorHandler:

DisplayADOError cn

End Sub

Here, the ShowError function attempts to open a Recordset object against a

nonexistent table At the beginning of this function, the On Error statement enables

Visual Basic’s error handler In this case, the On Error statement causes the program

to branch to the ErrorHandler label when a trappable error is encountered

Executing the Open method with a nonexisting table causes the ADO object

framework to generate a run-time error, which, in turn, causes the program

execution to resume with the first statement following the label In this example, the

DisplayADOError subroutine is executed following the invalid Open attempt

The following code listing shows how the DisplayDAOError subroutine uses

DAO’s Error object and Errors collection to display information about an ADO error

condition in a simple message box:

Private Sub DisplayADOError(cn As ADODB.Connection)

Dim er As ADODB.Error

For Each er In cn.Errors

MsgBox "Number: " & er.Number & vbCrLf & _

"Source: " & er.Source & vbCrLf & _

"Text: " & er.Description

Next

In this subroutine, an ADO Connection object is passed in as a parameter The ADO Errors collection is contained in the Connection object Next, a new ADO Error object named er is declared, and a For Each loop iterates through the ADO Errors collection The loop is required because the ADODB Errors collection can contain multiple Error objects where each Error object represents a different error condition With the For Each loop, the values of the Number, Source, and Description properties are displayed in a message box The Number property of the ADO Error object contains the ADO error message number, while the Source property identifies the source object that fired the error As you might expect, the Description property contains the error condition’s text description Figure 8-17 shows the message box that the DisplayADOError subroutine displays

Advanced Database Functions Using ADO

You’ve now seen how to use the basic ADO Connection, Recordset, and Command objects to query and update the SQL Server database In this section, you see how

to use some of the more advanced ADO functions, such as how to perform updates with batch cursors and commit and roll back transactions

Batch Updates

Batch updates allow all the changes made to a Recordset object to be written back

to the data source all at once Batch updates are most useful when you are working with disconnected Recordset sets such as you might use in Web-based applications With batch updates, the Recordset object is updated using the normal AddNew, Update, and Delete methods After all the changes have been made to the Recordset object, the BatchUpdate method is used to post the entire batch of changes to the database The client Batch cursor library generates a SQL query to synchronize the

Figure 8-17 ADO error handling

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local Recordset object and the data on the remote SQL Server system The following

example illustrates how to use the ADO Recordset object’s BatchUpdate method:

Private Sub BatchUpdate(cn As ADODB.Connection)

Dim rs As New ADODB.Recordset

Dim i As Integer

'Pass in the SQL, Connection, Cursor type,

' lock type and source type

rs.Open "Select Dep_ID, Dep_Name From Sales.SalesDepartment", _

cn, adOpenKeyset, adLockBatchOptimistic, adCmdText

'Add 50 rows to the Sales.SalesDepartment table

For i = 1 To 50

rs.AddNew

rs!Dep_ID = i

rs!Dep_Name = "Add Batch Department " & CStr(i)

rs.Update

Next

rs.UpdateBatch

'Display the new rows in a grid

DisplayKeysetGrid rs, Grid, 1

rs.Close

End Sub

This code is much like the standard ADO cursor update example presented earlier

in this chapter in the section “Updating Rows with a Recordset.” However, one

important difference exists The Recordset object’s lock type parameter is assigned

the constant adLockBatchOptimistic This tells ADO the Recordset object will use a

batch cursor After the Recordset object is opened, the AddNew and Update methods

are used to add 50 rows to the local Recordset Important to note is that unlike a

standard keyset cursor, which immediately propagates the new rows to the data

source, the batch cursor doesn’t update the data source until the UpdateBatch method

executes Then all the updated rows are written to the base tables

TIP

The CancelBatch method can be used to cancel all the pending changes that would be performed

by an UpdateBatch operation.

Using Transactions

Transactions enable you to group together multiple operations that can be performed

as a single unit of work This helps to ensure database integrity For instance,

transferring funds from your savings account to your checking account involves multiple database operations, and the transfer cannot be considered complete unless all the operations are successfully completed A typical transfer from your savings account to your checking account requires two separate, but related, operations: a withdrawal from your savings account and a deposit to your checking account If either operation fails, the transfer is not completed Therefore, both these functions are considered part of the same logical transaction In this example, both the

withdrawal and the deposit would be grouped together as a single transaction If the withdrawal operation succeeded, but the deposit failed, the entire transaction could

be rolled back, restoring the database to the condition it had before the withdrawal operation was attempted SQL Server supports transactions, but not all databases do

Rolling Back Transactions

In ADO, transactions are enabled in the Connection object The Connection object’s RollbackTrans method can be used to restore the database to the state it was in before the transaction occurred The following example shows how to use the RollbackTrans method:

Private Sub TransRollBack(cn As ADODB.Connection)

Dim rs As New ADODB.Recordset

'Start a transaction using the existing Connection object

cn.BeginTrans

'Execute SQL to delete all of the rows from the table

cn.Execute "Delete Sales.SalesDepartment"

'Now Rollback the transaction - the table is unchanged

cn.RollbackTrans

'Create a recordset to display the unchanged table

rs.Open "Select * From Sales.SalesDepartment", cn, , , adCmdText DisplayForwardGrid rs, Grid

rs.Close

End Sub

In this example, executing the BeginTrans method of the Connection object named cn signals to the database that a transaction is about to begin Then the

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Connection object’s Execute method is used to issue a SQL Delete statement that

deletes all the rows in the Sales.SalesDepartment table Instead of committing

that change to the database, however, the Connection object’s RollbackTrans

method is used to undo the transaction, restoring the original contents of the Sales

SalesDepartment table A rollback would also be performed if a network failure or

system crash prevented the Commit from being successfully executed A Recordset

object is created and displayed to illustrate that the table’s contents were unchanged

after the RollBackTrans method

TIP

SQL Server maintains database modifications in a transaction log file, which contains a serial

record of all the modifications that have been made to a database The transaction log contains

both before and after images of each transaction.

Committing Transactions

When a transaction is successfully completed, the Connection object’s CommitTrans

method writes the transaction to the database In the following example, you see

how to use ADO to begin a transaction and then commit that transaction to the SQL

Server database:

Private Sub TransCommit(cn As ADODB.Connection)

Dim rs As New ADODB.Recordset

'Start a transaction using the existing Connection object

cn.BeginTrans

'Execute SQL to delete all of the rows from the table

cn.Execute "Delete Sales.SalesDepartment"

'Commit the transaction and update the table

cn.CommitTrans

'Create a recordset to display the empty table

rs.Open "Select * From Sales.SalesDepartment", cn, , , adCmdText

DisplayForwardGrid rs, Grid

rs.Close

End Sub

Again, executing the BeginTrans method of the Connection object signals to

the database that a transaction is about to begin, and the Execute method is used to

issue a SQL Delete statement This time, however, the changes are committed to the

database using the Connection object’s CommitTrans method Finally, a Recordset object is opened to illustrate that the table’s contents were deleted following the CommitTrans method

Summary

While ADO provides similar functionality to both the older DAO and RDO object frameworks, ADO’s more-flexible object model allows it to be used effectively for a wider range of applications The DAO object model was primarily designed around the Jet engine, and the RDO object model was primarily designed for ODBC data access; however, the ADO object model was built around OLE DB Unlike Jet and ODBC, which are both geared toward database access, OLE DB is intended to provide heterogeneous data access to a number of different data sources OLE DB provides access to a variety of data sources, including Excel spreadsheets, Active Directory, and Exchange, in addition to relational databases such as SQL Server Bear in mind that ADO is best suited for maintaining older COM-based

applications Microsoft recommends that all new SQL Server 2005 applications

be written using ADO.NET and the NET Framework as you saw in Chapter 7

CHAPTER

9 Reporting Services

IN THIS CHAPTER

Reporting Services Architecture

Report Server Report Manager Reporting Services Configuration and Management Tools

Report Authoring Tools Programmability Accessing Reports Report Authoring

Copyright © 2006 by The McGraw-Hill Companies Click here for terms of use

One of the most exciting enhancements found in SQL Server 2005 is Reporting

Services Reporting Services was first introduced as an add-on to SQL Server

2000 and provided customers with a comprehensive reporting platform Because SQL Server has always been an easy-to-implement relational database platform,

it has been very popular for department-level implementations as well as a database platform for small and medium-sized businesses However, SQL Server had no built-in tools that were capable of generating reports, so many companies started using desktop reporting tools like Microsoft Access Many medium- and larger-sized organizations adopted more powerful third-party reporting products such as Business Object’s Crystal Reports

The inclusion of Reporting Services in SQL Server 2005 has changed all of that Reporting Services is a server-based reporting service that goes beyond the capabilities of simple reporting solutions like Access Reporting Services provides

an extensive environment for designing, managing, and deploying reports to local departments or the entire organization You can build reports based on relational or multidimensional data from SQL Server, Analysis Services, any Microsoft NET data provider such as ODBC or OLE DB, or even Oracle You can create ad hoc reports that use predefined models and data sources, or create tabular, matrix, and free-form reports Reporting Services not only provides the ability to graphically design reports but also enables you to securely deploy those reports across the enterprise rendered

in a variety of different formats, including Web-based HTML reports, Windows-based rich client reports, and reports rendered for mobile devices In the first part of this chapter, you’ll get an overview of the architecture used by SQL Server 2005’s Reporting Services In the second part of this chapter, you get a look at how you design reports using the report designer and report wizard Then you see how to manage and deploy reports using Reporting Services

Reporting Services Architecture

SQL Server 2005’s Reporting Services isn’t just a report design tool Instead, it’s

a complete reporting platform that enables the creation of reports, stores report definitions, provides secure access to reports, renders reports in a variety of different output formats, schedules report delivery, enables the deployment of those reports, and allows for programmability and extensibility features

Reporting Services provides a middle-tier server that runs under IIS (Internet Information Services) If IIS is not present on the system running the installation,

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the option to install Reporting Services will not be present on SQL Server 2005’s

installation dialogs While Reporting Services can be installed on the same server

system as the SQL Server database engine, for improved scalability it’s usually

better to install Reporting Services on a separate server

NOTE

Reporting Services is licensed as a part of SQL Server 2005 and does not require any separate

licensing for use on a single system However, it does require an additional license if you

implement it on a separate system.

SQL Server 2005 Reporting Services includes several applications It’s a server-based

subsystem that’s designed to enable the creation, management, and deployment of reports

across the enterprise You can see an overview of the Reporting Service architecture

shown in Figure 9-1

Reporting Services Components

As you can see in Figure 9-1, Reporting Services consists of a variety of interrelated

components These components include processing components, graphical and

command-prompt tools, and programmatic interfaces that facilitate development of

reports in a managed environment

Report Designer Report Builder

Reporting Services Database

Reporting Services

Reporting Manager

HTML Excel Web Archive PDF TIFF CSV XML

IIS Report Server

Data Sources

Figure 9-1 Reporting Services architecture

Report Server

The Report Server is the core component in Reporting Services The Report Server processes report requests and renders reports in the desired output format Report Server functions also include processing of report models, distribution of reports, security enforcement, and controlling user access to items and operations

Report Manager

The Report Manager is a Web-based application that enables the DBA or reporting administrator to control the security and overall management attributes of the reports created using Reporting Services The Report Manager is used to specify report change authority as well as report access authority It can also be used to set up delivery schedules for Reporting Services reports

Reporting Services Configuration and Management Tools

Reporting Services includes two configuration tools you can use to configure, deploy, upgrade, and manage local or remote report server instances:

䉴 The Reporting Services Confi guration tool

䉴 The Report Server command-prompt utilities

Report Authoring Tools

Reporting Services includes several tools for creating, publishing, and managing reports

䉴 The Report Designer

䉴 The Report Model Designer

䉴 The Report Builder

The Report Designer enables you to visually design reports as well as control their deployment and is accessed through the Business Intelligence (BI) Development Studio The Report Model Designer is the tool used to describe the metadata from a data source that is incorporated into ad hoc reports The Report Builder then uses the report model definitions created with the Report Model Designer to generate a query to retrieve the requested data, and create and publish the report