Level 56
This is a belongsToMany relationship with a_b as pivot table, not a hasManyThrough (which chains two hasMany).
Jun 1, 2015
5
Level 1
About many to many relationship
Now I have a pretty standard many to many relationship by establishing 3 tables:
table a: id, value
table b: id, value
table a_b: a_id, b_id
now when i want to access table b by table a, i have a class like this:
class a extends Model { protected $table = 'a'; public function b() { return $this->hasManyThrough('a','a_b', 'a_id','id'); } }
and i get an error message of such when i call a::find(1)->b in php:
SQLSTATE[42S22]: Column not found: 1054 Unknown column 'a_b.id' in 'on clause' (SQL: select b.*, a_b.a_id from b inner join a_b on a_b.id = a.id where a.id = 25)
pretty obvious the problem is a_b.id is not editable from model definition. is it really the case? what can i do if im not possible to change the database?
Level 1
Is it possible if i can know how exactly belongsToMany relationship is different from hasMany ? I am a bit confused about when to use which
Level 88
You can find all the information in here: http://laravel.com/docs/5.0/eloquent#relationships
Level 56
@orbbli here in your example a can have many b and b can have many a. It is a many to many relationship, named as a belongsToMany b and b belongsToMany a with laravel.
A hasManyThrough is when for example Group which hasMany User which hasMany Post. Here if you want all the posts written by the users of a group, you can define a hasManyThrough relationship between Group and Post (through User).
1 like
Level 1
Thanks for the explain. One last question, so when we are defining a many-to-many relationship, is it we shouldnt use "hasMany" but rather stick with "belongsToMany" on both sides?
Please or to participate in this conversation.