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rfc_pdo_subclasses.md

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PHP RFC: PDO driver specific sub-classes

Introduction

PDO is a generic database class. Some of the databases it supports have functionality that is specific to that database.

For example, when connected to an SQLite database, the sqlite specific function PDO::sqliteCreateFunction is available.

This is a slightly terrible way of doing things. And is an example of code that was snuck in before the RFC process was in place.

This RFC continues a discussion on internals of reimplementing this functionality 'properly'.

Proposal

The proposal has three parts:

  • Add new subclasses of PDO
  • Add PDO::connect to be able to create them
  • Add DB specific function to those subclasses.

Add new subclasses of PDO

There will be one subclasses for each known PDO support DB connection:

  • PDODblib
  • PDOFirebird
  • PDOMysql
  • PDOOci
  • PDOOdbc
  • PDOPgsql - definitely
  • PDOSqlite - definitely

Each of these subclasses will expose functionality that exists that is peculiar to that DB, and not present in the generic PDO class. e.g. PDOSqlite::createFunction() should be there rather than on PDO::sqliteCreateFunction.

Add a way of creating them through PDF static factory method

Add a static factory method to PDO called connect. During the connect process, the exact type of database being connected to will be checked, and if it is a DB that has a specific sub-class, return that sub-class instead of a generic PDO object

class PDO
{
    public static function connect(string $dsn [, string $username [, string $password [, array $options ]]]) {

        if (connecting to SQLite DB) {
            return new PDOSqlite(...);
        }


        return new PDO(...);
    }
}

PDO::connect will return the appropriate sub-class when connecting to specific type of DB.

Add DB specific function to those subclasses.

Backward Incompatible Changes

None known. It might be inconvenient for people who are extending PDO class directly, and would like to extend the specific types. They would need to write their own connect functions, that wrap and proxy those specific types.

Proposed PHP Version(s)

PHP 8.2

Open Issues

There are the known current issues.

Should the sub-classes only be avaiable when support for that DB is compiled in?

e.g. should PDOSqlite exist if PHP was compiled without PDO_SQLITE compilted in? Probaby not.

Create all DB sub-classes?

Should all DBs have sub-classes created now, or should they be added when someone requests it?

When to deprecate old function on PDO

The method PDO::sqliteCreateFunction should probably be deprecated and removed at 'some point'. Although this cleanup should happen, the position of this RFC is that it's very low priority.

8.2 - PDO subclassses become available 9.0 - calls to PDO::sqliteCreateFunction start raising deprecation notice. 10.0 - method PDO::sqliteCreateFunction is removed, and that functionality can only be accessed through PDOSqlite

Removing the methods that magically exist or not depending on the specific driver created would save some complication in the PDO code. So although there's not benefit in userland for deprecating the existing magic methods, there may be a complexity saving in maintenance.

Unaffected PHP Functionality

Everything else

Future Scope

Any DB specific stuff known about that were too much work to implement?

Proposed Voting Choices

Accept the RFC as proposed 2/3 required.

Patches and Tests

Links to any external patches and tests go here.

Implementation

After the project is implemented, this section should contain

  • the version(s) it was merged into
  • a link to the git commit(s)
  • a link to the PHP manual entry for the feature
  • a link to the language specification section (if any)

References

Links to external references, discussions or RFCs

Rejected Features

Keep this updated with features that were discussed on the mail lists.