Laravel Eloquent ORM 时如何查询表中指定的字段

/** 
 * Find a model by its primary key. 
 *www.bcty365.com  
 * @param  mixed  $id 
 * @param  array  $columns 
 * @return \Illuminate\Database\Eloquent\Model|\Illuminate\Database\Eloquent\Collection|null 
 */ 
public function find($id, $columns = ['*']) 
{ 
    if (is_array($id)) { 
        return $this->findMany($id, $columns); 
    } 
 
    $this->query->where($this->model->getQualifiedKeyName(), '=', $id); 
 
    return $this->first($columns); 
} 

/** 
 * Execute the query and get the first result. 
 * 
 * @param  array   $columns 
 * @return mixed|static 
 */ 
public function first($columns = ['*']) 
{ 
    $results = $this->take(1)->get($columns); 
 
    return count($results) > 0 ? reset($results) : null; 
} 
 
/** 
 * Execute the query as a "select" statement. 
 * 
 * @param  array  $columns 
 * @return array|static[] 
 */ 
public function get($columns = ['*']) 
{ 
    if (is_null($this->columns)) { 
        $this->columns = $columns; 
    } 
 
    return $this->processor->processSelect($this, $this->runSelect()); 
} 

$data = ModelA::find($id, ['column1', 'column2']); 
 
$data = ModelA::first(['column1', 'column2']); 
 
$data = ModelA::where(['column1', '=', 'value'])->get(['column1', 'column2']);