2 or more One to Many relationships between two tables in rails

问题

I have two tables:

Users and Groups

a User has_many groups and a group, belongs_to a user:

u = User.last
u.groups 

Supposed I wanted a second list of different groups, for some strange reason. Where once again a User has may groups (called other_group in this example) and a group belongs to a User.

u = User.last
u.other_groups

How do I associate two models in this relationship, Twice using Active Record?

回答1:

You can do

class User
    has_many :groups, :class_name => "Group", :foreign_key => "group_id"
    has_many :other_groups, :class_name => "Group", :foreign_key => "other_group_id"

回答2:

Your User model could have two foreign keys (attributes in rails)

User.group_id
User.other_group_id

回答3:

You can do

User(user_id)  
Group(group_id)
UserGroup (id, user_id, group_id)

this allows you to have records with user_ids associated for different groups.
This way lets you have multiple user-group associations.

来源：https://stackoverflow.com/questions/30468368/2-or-more-one-to-many-relationships-between-two-tables-in-rails