PHP Application Development With ADODB (part 1) - A Little Insulation
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First up, let's get the lingo straight: what the heck is a database abstraction library anyway?
If you've worked with different databases, you've probably seen that each database operates in a slightly different manner from the others. The data types aren't always uniform, and many of them come with proprietary extensions (transactions, stored procedures et al) that aren't supported elsewhere. Additionally, the API to interact with these databases is not uniform; PHP itself comes with a different API for each supported database type,
For all these reasons, switching from one database to another is typically a complex process, one which usually involves porting data from one system to another (with the assorted datatyping complications), rewriting your code to use the new database API, and testing it to make sure it all works. And that's where a database abstraction layer can help.
Typically, a database abstraction layer functions as a wrapper around your code, exposing a set of generic methods to interact with a database server. These generic methods are internally mapped to the native API for each corresponding database, with the abstraction layer taking care of ensuring that the correct method is called for your selected database type. Additionally, most abstraction layers also incorporate a generic superset of datatypes, which get internally converted into datatypes native to the selected RDBMS.
In order to better understand the difference, consider the following diagram:
As you can see, without an abstraction layer in place, you need to use a different API call for each of the three database types. With an abstraction layer in place, however, you can transparently use a single, generic call, and have the abstraction layer convert it into the native API call.
A number of different abstraction layers are available for PHP, most notably the PEAR DBI, Metabase and PHPLib. The one I'm going to use in this article is named ADODB (Active Data Objects DataBase), and it's one of the most full-featured and efficient PHP abstraction libraries available today. Developed by John Lim, the library currently supports a wide variety of database systems, including MySQL, PostgreSQL, Oracle, Interbase, Microsoft SQL Server, Access, ODBC and others, and has been used in a number of well-known open-source PHP projects, including phpLens, PostNuke and Webodex.
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