laravel hasManyThrough on a belongsTo relationship

问题:

I have the following Eloquent relationships where

Farm -> hasOne -> Address as follows :

/**
 * \App\Address associated to the current farm.
 *
 * @return \App\Address
 */
public function address()
{
    return $this->hasOne('\App\Address');
} 

...then Address -> belongsTo -> Country as follows:

public function country()
{
    return $this->belongsTo('\App\Country','country_id','id');
}

... and I'm like to retrieve the Country model and get all associated farms using the country_id on the address table. I defined a hasManyThrough as follows:

/**
 * Get all of the farms for the country.
 */
public function farms()
{
    return $this->hasManyThrough('App\Farm', 'App\Address');
}

but it generates the following SQL:

select 
    `farms`.*, 
    `addresses`.`country_id` 
from `farms` 
inner join `addresses` on `addresses`.`id` = `farms`.`address_id` 
where `addresses`.`country_id` = 1

The SQL is looking for an address_id on the farms table. But the farm does not "belongTo" an address. Is there anyway to correct this or am I stuck needing a change to my schema?

Many thanks.

回答1:

In order for that to work you'll need to reverse the direction of Farm-Address relation:

class Farm extends Model {
  public function address() {
    return $this->belongsTo(Address::class);
  }
}

The reason is that Eloquent assumes that every "node" in hasManyThrough relation is kind of a parent for the next node, meaning the next node belongs to the previous node. Here if you want to get farms through address for given country, farm needs to point to address via address_id and address needs to point to country via country_id.