Rails idiom to avoid duplicates in has_many :through
Use Array's |=
Join Method.
You can use Array's |=
join method to add an element to the Array, unless it is already present. Just make sure you wrap the element in an Array.
role #=> #<Role id: 1, name: "1">
user.roles #=> []
user.roles |= [role] #=> [#<Role id: 1, name: "1">]
user.roles |= [role] #=> [#<Role id: 1, name: "1">]
Can also be used for adding multiple elements that may or may not already be present:
role1 #=> #<Role id: 1, name: "1">
role2 #=> #<Role id: 2, name: "2">
user.roles #=> [#<Role id: 1, name: "1">]
user.roles |= [role1, role2] #=> [#<Role id: 1, name: "1">, #<Role id: 2, name: "2">]
user.roles |= [role1, role2] #=> [#<Role id: 1, name: "1">, #<Role id: 2, name: "2">]
Found this technique on this StackOverflow answer.
As long as the appended role is an ActiveRecord object, what you are doing:
user.roles << role
Should de-duplicate automatically for :has_many
associations.
For has_many :through
, try:
class User
has_many :roles, :through => :user_roles do
def <<(new_item)
super( Array(new_item) - proxy_association.owner.roles )
end
end
end
if super doesn't work, you may need to set up an alias_method_chain.