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PORails3 Cache Sweeper for has_and_belongs_to_many association
 

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    <p>I have the following relationships modeled in a Rails3 application:</p> <pre><code>class User &lt; ActiveRecord::Base has_and_belongs_to_many :skills end class SkillsUser &lt; ActiveRecord::Base end class Skill &lt; ActiveRecord::Base has_and_belongs_to_many :users end </code></pre> <p>The "SkillsUser" model represents the many-to-many association between users and skills. In this way, when a User adds a new Skill, and said Skill already exists in the "skills" table (i.e "Java"), I simply create the relationship between the existing skill and the user in the skills_users table. All good.</p> <p>Within the User's view, I display a list of Skills. And I have a fragment caching block wrapped around those skills. </p> <pre><code>&lt;% cache([user,"skills"]) do %&gt; &lt;div id="skills-grid"&gt; &lt;% user.sorted_skills.each do |s| %&gt; ... &lt;% end %&gt; &lt;/div&gt; &lt;% end %&gt; </code></pre> <p>On a separate edit page, a User can add or delete a Skill. This action simply creates or removes a skills_users record. And when this happens, I need to invalidate the fragment cache so that the skills render appropriately on the User view. </p> <p>So I created a CacheSweeper who's purpose in life is to observe the skills_users relationship. Here's the controller:</p> <pre><code>class SkillsController &lt; ApplicationController autocomplete :skill, :name cache_sweeper :skill_user_sweeper def create @user = User.find(params[:user_id]) #Make sure the current user has access to #associate a skill to the user in the request if(@user.id = current_user.id) SkillsHelper.associate_skill(@user,params[:skill][:name]) @skill = Skill.find_by_name(params[:skill][:name]) end respond_to do |format| format.js end end def destroy @skill = Skill.find_by_id(params[:id]) @user = User.find_by_id(params[:user_id]) #Destroy the relationship, not the skill @user.skills.delete(@skill) if(@skill.can_be_tweaked_by?(current_user)) respond_to do |format| format.js end end end </code></pre> <p>And here's the sweeper:</p> <pre><code>class SkillUserSweeper &lt; ActionController::Caching::Sweeper observe SkillsUser def after_create(skill_user) expire_cache_for(skill_user) end def after_update(skill_user) expire_cache_for(skill_user) end def after_destroy(skill_user) expire_cache_for(skill_user) end private def expire_cache_for(skill_user) expire_fragment([skill_user.user,"skills"]) end end </code></pre> <p>The problem is, after adding or removing a skills_users record (after "create" or "destroy" on the SkillsController), the sweeper is never invoked. I have other sweepers working within my project, but none of them observe many-to-many associations.</p> <p>My question, then, is how does one create a CacheSweeper to observe a "has_and_belongs_to_many" association?</p>
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