Extending model

I found an interesting scenario and please help me to see whether it is an issue.
I defined the table as following:
Table:t_orderinfo

Columns:
id
int AI PK
order_id
varchar(100) PK
payment_status int
company_id varchar(100)
payment_amount  decimal(10,2)
create_time datetime
update_time datetime

And I defined my entity
class Order extends Entity
{
    protected $attributes = [
        'order_id' => null,       // Represents a username
        'company_id' => null,
        'payment_amount' => null,
        'payment_status' => null
    ];
}

And my Model

class OrderModel extends Model
{
    protected $DBGroup = 'default';
    protected $table      = 't_orderinfo';
    protected $primaryKey = 'id';
    protected $returnType    = 'App\Entities\Order';
    protected $useSoftDeletes = false;

    protected $allowedFields = [
        'order_id', 
        'payment_status',
        'company_id',
        'payment_amount'
    ];

    protected $useTimestamps = true;
    protected $createdField  = 'create_time';
    protected $updatedField  = 'update_time';

    protected $validationRules    = [];
    protected $validationMessages = [];
    protected $skipValidation     = false;
}

And wired thing is , when set the primaryKey as id, I can successfully save the record, but when I use order_id as my PK, the save method also return true, but there is no record in the database.

Is there anyone can support me?