Has_one or Has_many?

I have four models.

Application, Permission, User and AppPermissions

My AppPermission looks like:

AppPermission   Application    Permission   User
      1              1              1         1
      2              1              2         2
      3              1              3         3
      4              1              4         4

So an Application can have different permission from different Users.

Model: AppPermission:
belongs_to :application
belongs_to :permission
belongs开发者_开发百科_to :user

What about Application , Permission and User ? Where to use has_many through or has_one through?

Application:
has_many :users
has_many :permissions

For users, you need more information, do you have more than one application? if so then:

User:
has_many :applications
has_many :appPermissions

Permission:
has_many :appPermissions
belongs_to :application

I don't see use case for having has_many :through with a three-way association. What a point having all permissions for a user without mentioning what application they are for? Most probably you will need queries like:

user.app_permissions.find_all_by_application_id(application).map(&:permission)

or

user.app_permissions.find_by_application_id_and_permission_id(application, permission)

All you need for these queries:

User:
has_many :app_permissions

AppPermission:
belongs_to :permission