barcode generator in vb.net codeproject Managing SQL Transactions in Software

Generate Code39 in Software Managing SQL Transactions

Managing SQL Transactions
Scanning ANSI/AIM Code 39 In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
ANSI/AIM Code 39 Encoder In None
Using Barcode encoder for Software Control to generate, create Code39 image in Software applications.
SET TRANSACTION Database at beginning of transaction
Decoding Code 3/9 In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
Painting Code 3/9 In Visual C#.NET
Using Barcode generation for .NET framework Control to generate, create ANSI/AIM Code 39 image in VS .NET applications.
START TRANSACTION
Code39 Printer In .NET Framework
Using Barcode maker for ASP.NET Control to generate, create Code 39 Full ASCII image in ASP.NET applications.
Code 39 Extended Maker In VS .NET
Using Barcode encoder for VS .NET Control to generate, create Code 39 image in Visual Studio .NET applications.
SET CONSTRAINTS (DEFERRED)
Draw Code-39 In Visual Basic .NET
Using Barcode generation for .NET Control to generate, create Code 39 Extended image in Visual Studio .NET applications.
USS Code 39 Generator In None
Using Barcode encoder for Software Control to generate, create Code-39 image in Software applications.
SQL statements
Creating Data Matrix ECC200 In None
Using Barcode creator for Software Control to generate, create Data Matrix image in Software applications.
Making GS1 128 In None
Using Barcode drawer for Software Control to generate, create GS1 128 image in Software applications.
SET CONSTRAINTS (IMMEDIATE)
Creating Bar Code In None
Using Barcode generator for Software Control to generate, create barcode image in Software applications.
Make Code 128C In None
Using Barcode creator for Software Control to generate, create Code 128A image in Software applications.
Successful statement execution
Code 2 Of 7 Creation In None
Using Barcode creator for Software Control to generate, create Codabar image in Software applications.
USS Code 39 Reader In Visual C#
Using Barcode recognizer for Visual Studio .NET Control to read, scan read, scan image in .NET framework applications.
Unsuccessful statement execution
Generating ANSI/AIM Code 128 In Objective-C
Using Barcode generation for iPhone Control to generate, create Code 128A image in iPhone applications.
Make Code 128 Code Set B In None
Using Barcode encoder for Excel Control to generate, create Code 128B image in Office Excel applications.
ROLLBACK
Reading Barcode In Visual Basic .NET
Using Barcode Control SDK for Visual Studio .NET Control to generate, create, read, scan barcode image in .NET framework applications.
Print UPC-A In .NET
Using Barcode drawer for Reporting Service Control to generate, create UPC Symbol image in Reporting Service applications.
COMMIT
Drawing Barcode In VB.NET
Using Barcode generation for VS .NET Control to generate, create bar code image in VS .NET applications.
Drawing UPC-A In Visual Basic .NET
Using Barcode generation for .NET framework Control to generate, create UPCA image in VS .NET applications.
Database updated
Figure 16-5
Deferring constraints in a transaction
In order to defer or apply the constraints within a transaction, you must use the SET CONSTRAINTS statement, as shown in the following syntax: SET CONSTRAINTS { ALL | <constraint names> } { DEFERRED | IMMEDIATE } As you can see from the syntax, you must choose from two sets of options. The first set of options allows you to specify the deferrable constraints that will be affected by the statement. If the statement should apply to all deferrable constraints, you can use the ALL keyword; otherwise, you must list the constraint names, separated by a column. You can specify only deferrable constraints in the SET CONSTRAINTS statement. The next set of options you must specify is whether to defer the application of the identified constraints (DEFERRED) or to apply them immediately (IMMEDIATE). You should defer constraints before you insert or modify data, and you should apply constraints after you ve modified that data. Normally, you will use the SET CONSTRAINTS statement in sets of two: one statement to defer the constraints and the other to apply them. However, you don t actually need to use the SET CONSTRAINTS statement to apply them because all constraints are applied before the transaction commits, whether or not the constraints have been explicitly applied. However, it is generally good practice to document all actions, so be sure to explicitly apply your constraints.
SQL: A Beginner s Guide
Now let s take a look at an example of a SET CONSTRAINTS statement that defers CONSTRAINT_1 and CONSTRAINT_2:
SET CONSTRAINTS CONSTRAINT_1, CONSTRAINT_2 DEFERRED;
As you can see, all you need to do is list the names of the constraints and the DEFERRED keyword. If you wanted your statement to apply to all deferrable constraints, you could have used the ALL keyword in place of the constraint names. Once you execute all the statements you need to execute, with regard to the deferred constraints, you can then apply the constraints to the new and modified data. To apply the constraints, use the following SET CONSTRAINTS statement:
SET CONSTRAINTS CONSTRAINT_1, CONSTRAINT_2 IMMEDIATE;
The only difference between this statement and the one that preceded this is that the IMMEDIATE keyword is used rather than DEFERRED.
NOTE
In order for you to use the SET CONSTRAINTS statement, your SQL implementation must support both the statement (or a similar statement) and deferrable constraints. If you cannot define deferrable constraints in your SQL database, the statement is not very useful. Oracle currently supports the SET CONSTRAINTS statement, but MySQL and SQL Server do not.
Create Savepoints in a Transaction
Often when you re setting up your transactions, you ll find that the set of actions you need to perform is straightforward and easily treated as a unit. However, there might be times when some of your transactions are not as simple as others and different degrees of complexity between actions makes treating them as one unit a little more difficult, even though you still want to keep them all within the same transaction. One way to deal with this type of situation is through the use of savepoints, which are designated markers within your transaction that act as rollback points for portions of your transaction.
NOTE
Support for savepoints varies across SQL implementations. Oracle and MySQL support the SAVEPOINT statement, but SQL Server uses a SAVE TRANSACTION statement instead.
Say, for example, that the first part of your transaction contains relatively straightforward code that, although not particularly complicated, can still demand a heavy load on your system s performance. Now suppose that later in your transaction you must perform more complex actions, actions that are more likely to cause a rollback than the first set of actions. However, you don t want your rollbacks to cause you to lose the work performed by the first set of actions because of the hit on performance. If you insert a savepoint between the
16:
Copyright © OnBarcode.com . All rights reserved.