LS DB ActiveRecord HABTM extension for conditional joins

db_activerecord_habtm_conditionaljoins.php

<?php
if (!class_exists('Db_ActiveRecord_habtm_ConditionalJoins')) {
  class Db_ActiveRecord_habtm_ConditionalJoins extends Db_ActiveRecord {
    public function get_relation_options($type, $name, &$has_primary_key, &$has_foreign_key) {
      $backtrace = debug_backtrace(false);
      $options = parent::get_relation_options($type, $name, $has_primary_key, $has_foreign_key);
      
      // TODO: I am very aware that this is a massive hack.  Still looking for a way around it.
      if ( $backtrace[1]['function'] == 'formFieldGetOptions' ) { return $options; }

      if ( $type == 'has_and_belongs_to_many' ) {
        $settings = $this->has_and_belongs_to_many[$name];
        if ( isset( $settings['join_conditions'] ) || isset( $settings['join_fields'] ) ) {
          $condition = ( isset( $settings['conditions'] ) ? ($settings['conditions']) . ' AND ' : null );
          $this->has_and_belongs_to_many[$name]['old_conditions'] = 
            ( isset( $settings['conditions'] ) ? $settings['conditions'] : null );
          
          $join_conditions = isset( $settings['join_conditions'] ) ? $settings['join_conditions'] : '';
          if ( isset( $settings['join_fields'] ) ) {
            if ( $join_conditions ) {
              $join_conditions  .= ' AND ';
            }
            $fields = array();
            foreach ( $settings['join_fields'] as $field_name => $value ) {
              $fields[] = "{$field_name}='" . mysql_real_escape_string( $value ) . "'";
            }
            $join_conditions .= '(' . join(' AND ', $fields) . ')';
          }
          if ( $join_conditions ) {
            $options['conditions'] = '(' . $condition . "({$join_conditions})" . ')';
          }
        }
      }
      return $options;
    }
    
    protected function custom_relation_save() {
      foreach ($this->changed_relations as $action => $relation) {
        foreach ($relation as $name => $info) {
          if ($info['type'] == 'has_and_belongs_to_many') {
            // Most of the following code is taken from db_activerecord.php in apply_relations_changes()
            $defaults = array(
              'class_name' => Phpr_Inflector::classify($name)
            );
            if (is_array($info['relation'])) {
              $options = array_merge($defaults, $info['relation']);
            } else {
              $options = array_merge($defaults, array('class_name' => Phpr_Inflector::classify($info['relation'])));
            }
            // We're only handling the polymorphic associations
            if ( !isset( $options['join_fields'] ) ) { continue; }

            // Create model
            $object = new $options['class_name']();
            if (is_null($object)) {
              throw new Phpr_SystemException('Class not found: '.$options['class_name']);
            }

            if (!isset($options['primary_key'])) {
              $options['primary_key'] = Phpr_Inflector::foreign_key($this->table_name, $this->primary_key);
            }

            if (!isset($options['foreign_key'])) {
              $options['foreign_key'] = Phpr_Inflector::foreign_key($object->table_name, $object->primary_key);
            }

            if (!isset($options['join_table'])) {
              $options['join_table'] = $this->get_join_table_name($this->table_name, $object->table_name);
            }
            if ($action == 'bind') {
              foreach ( $info['values'] as $value ) {
                $fields_to_set = array(
                  $options['primary_key'] => $this->{$this->primary_key}, 
                  $options['foreign_key'] => $value
                );
                // Merge the values if we're joining with additional fields
                if ( isset( $options['join_fields'] ) ) {
                  $fields_to_set = array_merge(
                    $fields_to_set,
                    $options['join_fields']
                  );
                }
                
                $this->sql_insert(
                  $options['join_table'], 
                  $fields_to_set
                );
              }
            } elseif ($action == 'unbind') {
              $delete_statement = Db::where( 
                $options['primary_key'] . ' = ?', 
                $this->{$this->primary_key}
              )->where(
                $options['foreign_key'] . ' IN (?)', 
                array($info['values'])
              );
              // Make sure to add the additional fields
              if ( isset( $options['join_fields'] ) ) {
                foreach ( $options['join_fields'] as $field_name => $value ) {
                  $delete_statement->where( $field_name . '=?', array($value) );
                }
              }
              $this->sql_delete(
                $options['join_table'], 
                $delete_statement
              );
            }
            unset ( $this->changed_relations[$action] );
          } // 'has_and_belongs_to_many'
        }
      } // foreach
    } // custom_relation_save
  }
}

Example conditions.php

<?php
    public $has_and_belongs_to_many = array(
      'add_on_order_status'=>array(
        'class_name'=>'Shop_StatusTransition', 
        'primary_key'=>'psinventory_param_id', 
        'foreign_key' => 'shop_status_transition_id', 
        'join_table' => 'psinventory_params_shop_status_transitions',
        'join_fields' => array(
          'transition_flag' => 'active'
        )
      ),
      'remove_on_order_status'=>array(
        'class_name'=>'Shop_StatusTransition', 
        'primary_key'=>'psinventory_param_id', 
        'foreign_key' => 'shop_status_transition_id', 
        'join_table' => 'psinventory_params_shop_status_transitions',
        'join_fields' => array(
          'transition_flag' => 'reclaim'
        )
      ),
      'update_at_order_status'=>array(
        'class_name'=>'Shop_OrderStatus',
        'primary_key'=>'psinventory_param_id', 
        'foreign_key' => 'shop_status_transition_id', 
        'join_table' => 'psinventory_params_shop_status_transitions',
        'join_fields' => array(
          'transition_flag' => 'order_status'
        )
      )
    );