$a=Model::find('blcu');
 echo $a->id; //结果为0

["attributes":protected]=>
 array(16) {
 ["id"]=>
 string(4) "blcu"

 public function getAttributeValue($key)
 {
  $value = $this->getAttributeFromArray($key);


  if ($this->hasGetMutator($key)) {
   return $this->mutateAttribute($key, $value);
  }


  if ($this->hasCast($key)) {
   return $this->castAttribute($key, $value); //这一行是导致数值改变的地方
  }


  if (in_array($key, $this->getDates()) && ! is_null($value)) {
   return $this->asDateTime($value);
  }

  return $value;
 }

 protected function castAttribute($key, $value)
 {
  if (is_null($value)) {
   return $value;
  }

  switch ($this->getCastType($key)) { 
   case 'int':
   case 'integer':
    return (int) $value; //这一行

 protected function getCastType($key)
 {
  return trim(strtolower($this->getCasts()[$key]));
 }

 public function getCasts()
 {

  if ($this->getIncrementing()) { //如果Model了的$incrementing字段为True
   return array_merge([
    $this->getKeyName() => 'int', //返回id=>'int'
   ], $this->casts);
  }

  return $this->casts;
 }