This module is designed to be included into an Ability class. This will provide the “can” methods for defining and checking abilities.
class Ability include CanCan::Ability def initialize(user) if user.admin? can :manage, :all else can :read, :all end end end
Alias one or more actions into another one.
alias_action :update, :destroy, :to => :modify can :modify, Comment
Then :modify permission will apply to both :update and :destroy requests.
can? :update, Comment # => true can? :destroy, Comment # => true
This only works in one direction. Passing the aliased action into the “can?” call will not work because aliases are meant to generate more generic actions.
alias_action :update, :destroy, :to => :modify can :update, Comment can? :modify, Comment # => false
Unless that exact alias is used.
can :modify, Comment can? :modify, Comment # => true
The following aliases are added by default for conveniently mapping common controller actions.
alias_action :index, :show, :to => :read alias_action :new, :to => :create alias_action :edit, :to => :update
This way one can use params in the controller to determine the permission.
# File lib/cancan/ability.rb, line 173 def alias_action(*args) target = args.pop[:to] aliased_actions[target] ||= [] aliased_actions[target] += args end
Returns a hash of aliased actions. The key is the target and the value is an array of actions aliasing the key.
# File lib/cancan/ability.rb, line 180 def aliased_actions @aliased_actions ||= default_alias_actions end
# File lib/cancan/ability.rb, line 215 def attributes_for(action, subject) attributes = {} relevant_rules(action, subject).map do |rule| attributes.merge!(rule.attributes_from_conditions) if rule.base_behavior end attributes end
Defines which abilities are allowed using two arguments. The first one is the action you’re setting the permission for, the second one is the class of object you’re setting it on.
can :update, Article
You can pass an array for either of these parameters to match any one. Here the user has the ability to update or destroy both articles and comments.
can [:update, :destroy], [Article, Comment]
You can pass :all to match any object and :manage to match any action. Here are some examples.
can :manage, :all can :update, :all can :manage, Project
You can pass a hash of conditions as the third argument. Here the user can only see active projects which he owns.
can :read, Project, :active => true, :user_id => user.id
See ActiveRecordAdditions#accessible_by for how to use this in database queries. These conditions are also used for initial attributes when building a record in ControllerAdditions#load_resource.
If the conditions hash does not give you enough control over defining abilities, you can use a block along with any Ruby code you want.
can :update, Project do |project| project.groups.include?(user.group) end
If the block returns true then the user has that :update ability for that project, otherwise he will be denied access. The downside to using a block is that it cannot be used to generate conditions for database queries.
You can pass custom objects into this “can” method, this is usually done with a symbol and is useful if a class isn’t available to define permissions on.
can :read, :stats can? :read, :stats # => true
IMPORTANT: Neither a hash of conditions or a block will be used when checking permission on a class.
can :update, Project, :priority => 3 can? :update, Project # => true
If you pass no arguments to can
, the action, class, and object
will be passed to the block and the block will always be executed. This
allows you to override the full behavior if the permissions are defined in
an external source such as the database.
can do |action, object_class, object| # check the database and return true/false end
# File lib/cancan/ability.rb, line 124 def can(action = nil, subject = nil, conditions = nil, &block) rules << Rule.new(true, action, subject, conditions, block) end
Check if the user has permission to perform a given action on an object.
can? :destroy, @project
You can also pass the class instead of an instance (if you don’t have one handy).
can? :create, Project
Nested resources can be passed through a hash, this way conditions which are dependent upon the association will work when using a class.
can? :create, @category => Project
Any additional arguments will be passed into the “can” block definition. This can be used to pass more information about the user’s request for example.
can? :create, Project, request.remote_ip can :create Project do |project, remote_ip| # ... end
Not only can you use the can? method in the controller and view (see ControllerAdditions), but you can also call it directly on an ability instance.
ability.can? :destroy, @project
This makes testing a user’s abilities very easy.
def test "user can only destroy projects which he owns" user = User.new ability = Ability.new(user) assert ability.can?(:destroy, Project.new(:user => user)) assert ability.cannot?(:destroy, Project.new) end
Also see the RSpec Matchers to aid in testing.
# File lib/cancan/ability.rb, line 56 def can?(action, subject, *extra_args) match = relevant_rules_for_match(action, subject).detect do |rule| rule.matches_conditions?(action, subject, extra_args) end match ? match.base_behavior : false end
Defines an ability which cannot be done. Accepts the same arguments as “can”.
can :read, :all cannot :read, Comment
A block can be passed just like “can”, however if the logic is complex it is recommended to use the “can” method.
cannot :read, Product do |product| product.invisible? end
# File lib/cancan/ability.rb, line 140 def cannot(action = nil, subject = nil, conditions = nil, &block) rules << Rule.new(false, action, subject, conditions, block) end
Convenience method which works the same as “can?” but returns the opposite value.
cannot? :destroy, @project
# File lib/cancan/ability.rb, line 67 def cannot?(*args) !can?(*args) end
Removes previously aliased actions including the defaults.
# File lib/cancan/ability.rb, line 185 def clear_aliased_actions @aliased_actions = {} end
# File lib/cancan/ability.rb, line 223 def has_block?(action, subject) relevant_rules(action, subject).any?(&:only_block?) end
# File lib/cancan/ability.rb, line 227 def has_raw_sql?(action, subject) relevant_rules(action, subject).any?(&:only_raw_sql?) end
# File lib/cancan/ability.rb, line 231 def merge(ability) ability.send(:rules).each do |rule| rules << rule.dup end self end
# File lib/cancan/ability.rb, line 189 def model_adapter(model_class, action) adapter_class = ModelAdapters::AbstractAdapter.adapter_class(model_class) adapter_class.new(model_class, relevant_rules_for_query(action, model_class)) end