generate code 39 barcode using c# CREATING THE PRODUCT CATALOG: PART I in Visual C#.NET

Generator Code 39 Extended in Visual C#.NET CREATING THE PRODUCT CATALOG: PART I

The SQL queries you write must be sent somehow to the database engine for execution. As you learned in 2, you ll use PHP PDO to access the PostgreSQL server. Before writing the business tier code, you need to analyze and understand the possibilities for implementation. The important questions to answer before writing any code include the following: What strategy should you adopt for opening and closing database connections, when you need to execute an SQL query Which methods of PHP PDO should you use for executing database functions and returning the results How should you handle possible errors and integrate the error-handling solution with the error-handling code you wrote in 2 Let s have a look at each of these questions one by one, and then we ll start writing some code.

There are two main possible approaches you can take for this. The first is illustrated by the following sequence of actions, which needs to be executed each time the database needs to be accessed. 1. Open a connection to the database exactly before you need to execute a command on the database. 2. Execute the SQL query (or the database function) using the open connection, and get back the results. At this stage, you also need to handle any possible errors. 3. Close the database connection immediately after executing the command. This method has the advantage that you don t keep database connections for a long time (which is good because database connections consume server resources) and is also encouraged for servers that don t allow many simultaneous database connections. The disadvantage is the overhead implied by opening and closing the database connection all the time, which can be partially reduced by using persistent connections.

Note Persistent connections refers to a technology that attempts to improve the efficiency of opening

and closing database connections with no impact on functionality. You can learn more about this technology at http://www.php.net/manual/en/features.persistent-connections.php.

The alternative solution, and the one you ll use when implementing HatShop, can be described like this: 1. Open a connection to the database the first time you need to access the database during a request.

2. Execute all database functions (or SQL queries) through that connection without closing it. Here you also need to handle any possible errors. 3. Close the database connection when the client request finishes processing. Using this method, all database operations that happen for a single client request (which happens each time a user visits a new page of our site) will go through a single database connection, avoiding opening and closing the connection each time you need something from the database. You ll still use persistent connections to improve the efficiency of opening a new database connection for each client request. This solution is the one you will use for data access in the HatShop project.

Now you should learn the theory about how to put this in practice using PHP PDO. You ll effectively write the code a bit later, when building the added functionality into the web site. As explained in 2, you won t access PostgreSQL through PHP s PostgreSQLspecific database functions but through a database abstraction layer (PHP PDO). The PDO classes permit accessing various data sources using the same API (Application Programming Interface), so you won t need to change the PHP data access code or learn different dataaccess techniques when working with database systems other than PostgreSQL (but you might need to change the SQL code itself if the database you migrate to uses a different dialect). Using PHP PDO makes your life as a programmer easier in the long run. The important PHP PDO class you ll work with is PDO, which provides methods for performing various database operations.

Note In this book, you ll learn about the PHP PDO functionality as used in HatShop. For more details