属于通过方法

Question

我如何belongsToThrough通过中间国家表获得计划的货币？

这是我的数据库结构：

plan
    id - integer
    country_id - string // country.code

country
    code - string
    currency_id - string // currency.code

currency
    code - string

我需要currency()计划模型中的关系：

我试了几次都没有用。我想过这样的事情，但这只是返回空值：

class Plan extends \Illuminate\Database\Eloquent\Model
{
    public function currency()
    {
        return $this->belongsTo(
            Currency::class, // $related,
            'currency_id', // $foreignKey = null,
            'code', // $ownerKey = null,
            'country' // $relation = null
        );
    }

Answer 1

你需要两个BelongsTo关系：

class Plan extends \Illuminate\Database\Eloquent\Model
{
    public function country()
    {
        return $this->belongsTo(Country::class, 'country_id', 'code');
    }
}

class Country extends \Illuminate\Database\Eloquent\Model
{
    public function currency()
    {
        return $this->belongsTo(Currency::class, 'currency_id', 'code');
    }
}

$currency = $plan->country->currency;

如果您想一步获得货币：

class Plan extends \Illuminate\Database\Eloquent\Model
{
    public function getCurrencyAttribute()
    {
        return $this->country->currency;
    }
}

$currency = $plan->currency;