OOPHP_02.book Page 141 Friday, May 5, 2006 2:25 PM
How It’s Done In this application we take advantage of some of SQLite’s advanced capabilities. Both triggers and views will be used. A trigger, code that executes in response to an add, edit, or delete event, will be used to mimic a datestamp field—records will be automatically stamped whenever they are added or changed. Views are a convenient way of storing queries and can replace tables in the FROM clause of a SELECT statement. They can also be used with triggers so that “updating” a view updates the associated table. No database used in conjunction with PHP can escape comparison to MySQL. Where appropriate, I will point out differences in SQL syntax between SQLite and MySQL. Likewise, SQLite has a variety of different query methods. These will also be contrasted with MySQL functions. As you have seen, throwing exceptions rather than trapping errors makes for cleaner code. SQLite has a built-in OO interface, and there is an SQLiteException class. However, only the SQLite database constructor throws exceptions. By extending the SQLite database class, we can override the query methods so that a failed query also throws an exception. This derived class will also include data verification methods that make use of metadata extracted from the database. This will be done by querying the sqlite_master table and through the use of pragmas. A pragma modifies the way the SQLite library works but can also be used to query the database structure. We’re only interested in the second use. A limited number of functions are available for use with SQLite’s dialect of SQL. You’ll see how this shortcoming can be overcome by creating userdefined functions (UDFs).
Getting Started SQLite comes bundled with PHP 5, so all you have to do to install the database is run the db_install_script.php file. However, if you do things this way you’ll have to write code just to view your data or to examine the structure of your database. You might want to download the command-line version of SQLite instead. PHP 5, depending upon the subversion number, comes with SQLite versions 2.8.11 through 2.8.17. To find out which version is running on your system, display the results of the PHP function phpinfo in your browser and search for SQLite. For convenience, you might want to install the binary of sqlite in the same directory as your database. Creating a database is as simple as typing the name of the SQLite executable file at the command line followed by the database name—for example, sqlite resources.sqlite. Doing so will run sqlite and create or open an existing database of the specified name. You can now create a table using SQL from the command line. However, let me make one more suggestion. At some point you will want to dump your database, and if you have created it from the command line the output won’t be very readable.
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