Question

I have a configurable report. For each field that can be included on the report, there’s a key (stored in report preferences), a label, potentially an access level, and a SQL descriptor — something like foo as my_foo.

In a Java app, I would create a class called ReportField with each of the properties listed above. I’d use a private constructor, and list each of the fields in the class like this:

public final static ReportField FOO = new ReportField('foo', 'Foo', 1, 'foo as my_foo');

I’d probably create a static array of all of the fields, add a static method that allows a field to be looked up by key, and so forth. Then in other places I could write code like:

List<String> selectFields = new ArrayList<String>();
for (ReportPref pref : reportPrefs) {
    selectFields.add(ReportField.getByKey(pref.getField()).getFieldSql());
}

Apologies for the Java code, but hopefully you get my point.

Is there an idiomatic way to solve the same problem in PHP? I can think of a number of solutions — nested associative arrays will do the trick — but I’d like to avoid a hackish solution.

Answer 1

I don’t know Java super well, but you can do most of that – just have to do it differently, unless I misunderstand your question.

Data members on PHP classes can’t have runtime-calculated values, such as new object instances. So, this would not work

class ReportField
{
  public static $foo = new ReportField()
}

Note: final properties are not allowed except on methods

It’s actually really curious to me that you’re making one class responsible for two things – an object blueprint AND static storage for instances of itself as well.

Anyway, here’s what I think your code would look like in PHP

<?php

class ReportField
{
  public static $store = array();

  private
    $key,
    $label,
    $accessLevel,
    $sql;

  private function __construct( $key, $label, $accessLevel, $sql )
  {
    $this->key = $key;
    $this->label = $label;
    $this->accessLevel = $accessLevel;
    $this->sql = $sql;
  }

  public static function initializeStore()
  {
    if ( empty( self::$store ) )
    {
      self::$store['foo'] = new self( 'foo', 'Foo', 1, 'foo as my_foo' );
      // repeat
    }
  }

  public static function getByKey( $key )
  {
    if ( empty( self::$store ) )
    {
      self::initializeStore();
    }
    if ( isset( self::$store[$key] ) )
    {
      return self::$store[$key];
    }
    throw new Exception( __CLASS__ . " instance identified by key $key not found" );
  }

  public function getFieldSql()
  {
    return $this->sql;
  }
}

// Usage
$selectFields = array();
foreach ( $reportPrefs as $pref )
{
  $selectFields[] = ReportField::getByKey( $pref->getField() )->getFieldSql();
}