Module: CanCan::Ability

Included in:
Ability
Defined in:
lib/cancan/ability.rb

Overview

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

Instance Method Summary collapse

Instance Method Details

#alias_action(*args) ⇒ Object

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.



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# File 'lib/cancan/ability.rb', line 181

def alias_action(*args)
  target = args.pop[:to]
  validate_target(target)
  aliased_actions[target] ||= []
  aliased_actions[target] += args
end

#aliased_actionsObject

Returns a hash of aliased actions. The key is the target and the value is an array of actions aliasing the key.



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# File 'lib/cancan/ability.rb', line 195

def aliased_actions
  @aliased_actions ||= default_alias_actions
end

#attributes_for(action, subject) ⇒ Object



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# File 'lib/cancan/ability.rb', line 230

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

#authorize!(action, subject, *args) ⇒ Object

See ControllerAdditions#authorize! for documentation.



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# File 'lib/cancan/ability.rb', line 210

def authorize!(action, subject, *args)
  message = nil
  if args.last.is_a?(Hash) && args.last.key?(:message)
    message = args.pop[:message]
  end
  if cannot?(action, subject, *args)
    message ||= unauthorized_message(action, subject)
    raise AccessDenied.new(message, action, subject)
  end
  subject
end

#can(action = nil, subject = nil, conditions = nil, &block) ⇒ Object

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 nor 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


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# File 'lib/cancan/ability.rb', line 132

def can(action = nil, subject = nil, conditions = nil, &block)
  add_rule(Rule.new(true, action, subject, conditions, block))
end

#can?(action, subject, *extra_args) ⇒ Boolean

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

You can also pass multiple objects to check. You only need to pass a hash following the pattern { :any => [many subjects] }. The behaviour is check if there is a permission on any of the given objects.

can? :create, {:any => [Project, Rule]}

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.

Returns:

  • (Boolean)


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# File 'lib/cancan/ability.rb', line 62

def can?(action, subject, *extra_args)
  match = extract_subjects(subject).lazy.map do |a_subject|
    relevant_rules_for_match(action, a_subject).detect do |rule|
      rule.matches_conditions?(action, a_subject, extra_args)
    end
  end.reject(&:nil?).first
  match ? match.base_behavior : false
end

#cannot(action = nil, subject = nil, conditions = nil, &block) ⇒ Object

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


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# File 'lib/cancan/ability.rb', line 148

def cannot(action = nil, subject = nil, conditions = nil, &block)
  add_rule(Rule.new(false, action, subject, conditions, block))
end

#cannot?(*args) ⇒ Boolean

Convenience method which works the same as “can?” but returns the opposite value.

cannot? :destroy, @project

Returns:

  • (Boolean)


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# File 'lib/cancan/ability.rb', line 75

def cannot?(*args)
  !can?(*args)
end

#clear_aliased_actionsObject

Removes previously aliased actions including the defaults.



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# File 'lib/cancan/ability.rb', line 200

def clear_aliased_actions
  @aliased_actions = {}
end

#has_block?(action, subject) ⇒ Boolean

Returns:

  • (Boolean)


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# File 'lib/cancan/ability.rb', line 238

def has_block?(action, subject)
  relevant_rules(action, subject).any?(&:only_block?)
end

#has_raw_sql?(action, subject) ⇒ Boolean

Returns:

  • (Boolean)


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# File 'lib/cancan/ability.rb', line 242

def has_raw_sql?(action, subject)
  relevant_rules(action, subject).any?(&:only_raw_sql?)
end

#merge(ability) ⇒ Object



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# File 'lib/cancan/ability.rb', line 246

def merge(ability)
  ability.rules.each do |rule|
    add_rule(rule.dup)
  end
  self
end

#model_adapter(model_class, action) ⇒ Object



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# File 'lib/cancan/ability.rb', line 204

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

#permissionsObject

Return a hash of permissions for the user in the format of:

{
  can: can_hash,
  cannot: cannot_hash
}

Where can_hash and cannot_hash are formatted thusly:

{
  action: array_of_objects
}


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# File 'lib/cancan/ability.rb', line 263

def permissions
  permissions_list = { can: {}, cannot: {} }

  rules.each do |rule|
    subjects = rule.subjects
    expand_actions(rule.actions).each do |action|
      if rule.base_behavior
        permissions_list[:can][action] ||= []
        permissions_list[:can][action] += subjects.map(&:to_s)
      else
        permissions_list[:cannot][action] ||= []
        permissions_list[:cannot][action] += subjects.map(&:to_s)
      end
    end
  end

  permissions_list
end

#unauthorized_message(action, subject) ⇒ Object



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# File 'lib/cancan/ability.rb', line 222

def unauthorized_message(action, subject)
  keys = unauthorized_message_keys(action, subject)
  variables = { action: action.to_s }
  variables[:subject] = (subject.class == Class ? subject : subject.class).to_s.underscore.humanize.downcase
  message = I18n.translate(nil, variables.merge(scope: :unauthorized, default: keys + ['']))
  message.blank? ? nil : message
end

#validate_target(target) ⇒ Object

User shouldn't specify targets with names of real actions or it will cause Seg fault

Raises:



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# File 'lib/cancan/ability.rb', line 189

def validate_target(target)
  error_message = "You can't specify target (#{target}) as alias because it is real action name"
  raise Error, error_message if aliased_actions.values.flatten.include? target
end