Pb转换重量

Question

我尝试使用一个类来转换重量，kg in gr .... 但我总是喜欢价值。

public function prepareRules() {
  $Db = Registry::get('Db');
  $Language = Registry::get('Language');

        $Qrules = $CLICSHOPPING_Db->prepare('select r.weight_class_from_id, 
                                              r.weight_class_to_id, 
                                              r.weight_class_rule 
                                      from :table_weight_classes_rules r, 
                                            :table_weight_classes c 
                                      where c.weight_class_id = r.weight_class_from_id
                                      ');
  $Qrules->setCache('weight-rules');
  $Qrules->execute();

  while ( $Qrules->fetch() ) {
    $this->weight_classes[$Qrules->valueInt('weight_class_from_id')][$Qrules->valueInt('weight_class_to_id')] = $Qrules->value('weight_class_rule');
  }

  $Qclasses = $Db->prepare('select weight_class_id, 
                                                weight_class_key, 
                                                weight_class_title 
                                          from :table_weight_classes 
                                          where language_id = :language_id
                                          ');
  $Qclasses->bindInt(':language_id', $Language->getID());

  $Qclasses->execute();

  while ( $Qclasses->fetch() ) {
    $this->weight_classes[$Qclasses->valueInt('weight_class_id')]['key'] = $Qclasses->value('weight_class_key');
    $this->weight_classes[$Qclasses->valueInt('weight_class_id')]['title'] = $Qclasses->value('weight_class_title');
  }
}

public function convert($value, $unit_from, $unit_to) {
  if ( $unit_from == $unit_to ) {
    $convert = number_format($value, $this->precision, static::getNumericDecimalSeparator(), static::getNumericThousandsSeparator());
    return $convert;
  } else {
    $convert = number_format($value * $this->weight_classes[(int)$unit_from][(int)$unit_to], $this->precision, static::getNumericDecimalSeparator(), static::getNumericThousandsSeparator());

    return $convert;
  }

如果我尝试转换某些东西 $ products_weight = $ Weight-＆gt; convert（5,2,3）;

5是重量（值）

2是kg（$ unit_from）

3是oz（$ unit_to）

var_dump($value); ==> ok
var_dump($this->weight_classes[(int)$unit_from][(int)$unit_to]); ==> always 0