Laravel 5.6急于加载特定列不会返回任何内容 [英] Laravel 5.6 Eager Loading specific column returns nothing

问题描述

我有两个类，Product和ProductFormat.该关系已正确定义，即我的产品hasMany ProductFormat.

I have two classes, Product and ProductFormat. The relationship is defined properly, my Product hasMany ProductFormat.

public function formats()
{
    return $this->hasMany(ProductFormat::class);
}

当我尝试使用特定列加载关系时，请按照文档中的说明进行操作( https://laravel.com/docs/5.6/eloquent-relationships#eager-loading )，它没有按预期运行.

When I'm trying to eager load the relationship with specific columns, as followed in the documentation (https://laravel.com/docs/5.6/eloquent-relationships#eager-loading), it's not working as expected.

例如，当我执行以下操作时:

For example, when I do the following:

Product::with('formats:id,upc')->get();

我得到我的产品，到处都是空格式.

I get my products, with empty formats everywhere.

{
    id: 1,
    formats: [ ]
}

但是，如果我执行以下操作:

However, if I do the following:

Product::with('formats')->get();

我得到了预期的格式，但是有太多不需要的列.

I get the expected formats, but it has too many non needed columns.

{
    id: 1,
    formats: [
        {
            id: 1,
            upc: "101862422191",
            weight: 8.46,
            weight_unit: "kg"
        }
   ]
}

推荐答案

您始终需要选择关系中涉及的外键/主键.也在急切加载中获取product_id，它将正常工作

You always need foreign key/primary key, involved in the relation, to be selected. fetch product_id too in eager load and it will work

Product::with('formats:id,upc,product_id')->get();

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