获得具有热切加载laravel 4的特定列

Question

我是laravel的新手,并创建一个基本的应用程序来控制关系.我实现了一对一的关系,并希望从基表和相关表中获取特定的列.我有两个表,即users和identity_cards.Relationship定义如下

class User extends Eloquent implements UserInterface, RemindableInterface {

    use UserTrait, RemindableTrait;

    /**
     * The database table used by the model.
     *
     * @var string
     */
     protected $table = 'users';

    /**
     * The attributes excluded from the model's JSON form.
     *
     * @var array
     */
    //protected $hidden = array('password', 'remember_token');

    protected $fillable = array('first_name','last_name','email','created_at','updated_at');

    public function identity_cards() 
    {
        return $this->hasOne('IdentityCard');
    }
}


class IdentityCard extends Eloquent {

    protected $table    = 'identity_cards';
    protected $fillable = array('issuance_date','expiry_date','issuance_location','user_id');
    public $timestamps  = false;

    public function user()
    {
       return $this->belongsTo('User');
    }
}

当我尝试检索所有列时,一切正常

$users = User::with('identity_cards')->get()->toArray();

但是当我试图从其中一个或两个表中获取特定列时,我得到一个空数组来对抗身份证表的记录

 $users = User::with(array('identity_cards'),function($query) {
                $query->select('issuance_location'); //getting specific column from identity card table
              }
          )->get(array("first_name"))->toArray();

针对以上陈述的结果如下: -

Array
(
    [0] => Array
    (
        [first_name] => User1
        [identity_cards] => 
    )

    [1] => Array
    (
        [first_name] => User2
        [identity_cards] => 
    )

    [2] => Array
    (
        [first_name] => User3
        [identity_cards] => 
    )

 )

这可以使用查询生成器实现,但我想要解决方案eloquent.为什么我得到一个空数组为我的相关表,即使我有数据.如何使用急切加载获取特定列？

Answer 1

1您需要始终选择primary key关系的父级和foreign key子级,否则Eloquent将无法匹配相关模型.

2传递给eager loading的Closure是数组的值,而不是with函数的第二个参数:

User::with(array('identity_cards' => function($query) {
            $query->select('issuance_location', 'user_id');
      }))->get(array('first_name', 'id'))->toArray();

3我会重新命名这种关系identity_card,因为hasOne它会更容易使用.