Laravel Model Relationships - What kind of relationship am I trying to create? - php

Question

I have got 3 models associated with this question; Country, Manufacturer and Region.
I've simplified the tables for the sake of this question. I don't think anything else in the tables or any of the other models are anything to do with the problem.
My tables are set up like so;
manufacturers
- id
- name
countries
- id
- name
regions
- id
- name
- manufacturer_id
- country_id
What I want to be able to do is to write $manufacturer->countries in my blade and have it spit out the countries that are associated with a given manufacturer.
The models are currently related to each other like this;
Country.php
public function manufacturers()
{
return $this->hasMany(Manufacturer::class);
}
public function regions()
{
return $this->hasMany(Region::class);
}
Region.php
public function manufacturer()
{
return $this->belongsTo(Manufacturer::class);
}
public function country()
{
return $this->belongsTo(Country::class);
}
and where I'm having the problem, Manufacturer.php
I think I need a hasMany relationship. I've already got;
public function regions()
{
return $this->hasMany(Region::class);
}
and I would have thought I would have needed;
public function countries()
{
return $this->hasManyThrough(Country::class,Region::class);
}
but that leads to this error;
Column not found: 1054 Unknown column 'countries.region_id' in 'on clause' (SQL: select `countries`.*, `regions`.`manufacturer_id` as `laravel_through_key` from `countries` inner join `regions` on `regions`.`id` = `countries`.`region_id` where `regions`.`manufacturer_id` = 4)
so I tried swapping the classes round to give;
public function countries()
{
return $this->hasManyThrough(Region::class,Country::class);
}
but that leads to;
Column not found: 1054 Unknown column 'countries.manufacturer_id' in 'field list' (SQL: select `regions`.*, `countries`.`manufacturer_id` as `laravel_through_key` from `regions` inner join `countries` on `countries`.`id` = `regions`.`country_id` where `countries`.`manufacturer_id` = 4)
Does anyone know how I should be setting my relationships up in order to achieve what I want?
I also tried a belongsToMany relationship, which did bring back the countries, but multiple instances of the same country. I just want one instance of each country that appears in the regions table for any given manufacturer.

Answer 1

You are actually dealing with the many-to-many relationship.
In your case regions is a pivot table.
Kindly check belongsToMany.

Answer 2

In Laravel, the best relationship to apply is many to many relationship. What this means as applied to your case is that 1 country can have multiple manufacturers and 1 manufacturer can be in multiple countries.
If that is the case, you don't need to create a regions table, but rather a pivot table. The default naming convention in laravel is (singular and om alphabetic order), that is, country_manufacturer table and it will contain (You can always add an extra variable known as pivot value):
country_manufacturer
- id
- name // pivot value
- manufacturer_id
- country_id
Then, in the models, add belongsToMany relationship, i.e.
In Manufacturer model (without pivot) :
public function countries()
{
return $this->belongsToMany(Manufacturer::class);
}
In Country Model (With pivot):
public function manufacturers()
{
return $this->belongsToMany(Country::class)->withPivot('name');
}
Hence, you will be able to call $country->manufacturers() which will give you a list of all the manufacturers in the $country and the reverse is true: $manufacturer->countries will give you all the countries the manufacturer is based in.