Handling Complex WHERE clauses with a PHP Query Builder

Question

There are several ActiveRecord styled query builder libraries out there. Some are stand alone and some come built into frameworks. However, they really have trouble with WHERE a

Answer 1

I worked quite a bit on the Zend_Db library, which includes a PHP class for constructing SQL queries. I decided to punt on trying to handle every imaginable SQL syntax in WHERE and HAVING clauses, for several reasons:

• PHP is a scripting language that parses and compiles code on every request (unless you use a bytecode cache). So the PHP environment is sensitive to bulky code libraries -- more so than Java or C# or Python or what have you. It's therefore a high priority to keep libraries as lean as we can.

  All of the Zend_Db library I worked on was about 2,000 lines of PHP code. By contrast, Java Hibernate is on the order of 118K lines of code. But that's not so much of an issue since a Java library is precompiled and doesn't have to be loaded on every request.

• SQL expressions follow a generative grammar that is more compact, and easier to read and maintain that any of the PHP-based construction you showed. Learning the SQL expression grammar is far easier than learning an API that can simulate it. You end up supporting a "simplified grammar." Or else you start out that way, and find yourself coerced by your user community into Feature Creep until your API is unusably complex.

• To debug an application that used such an API, you'd inevitably need access to the final SQL expression, so it's about the leakiest abstraction you can have.

• The only advantage to using a PHP-based interface for SQL expressions would be that it assists code-completion in smart editors and IDE's. But when so many of the operators and operands use string constants like '>=', you spoil any code-completion intelligence.

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update: I just read a good blog article "A Farewell to ORMs." The writer, Aldo Cortesi, suggests using the SQL Expression Language in Python's SQLAlchemy. Syntactic sugar and operator overloading that is standard in Python (but not supported in PHP) make this a very effective query-generating solution.

You might also look at Perl's DBIx::Class, but it ends up being pretty ugly.