Question

I have fairly simple problem but I can not think of the simple solution. I have 3 models.

class User < ActiveRecord::Base
  has_many :memberships
end

class Membership < ActiveRecord::Base
  belongs_to :user
  belongs_to :school
end

class School < ActiveRecord::Base
  has_many :memberships
end  

A User can create a membership for school(s). “membernumber” is given by school. So far so good.

Except one use case, where a membership record gets created by school without user_id value in memberships table.

In this case a record gets created with “membernumber”, “school_id” and empty “user_id” field.

What I want to do is, when a user tries to create his membership (using his “membernumber”) with a school, First I want to see if “user_id”, “membernumber”. school_id combination is unique if found (I used validates_uniqueness_of….).

If record not found than check a record/association with “membernumber” and school exists and it’s user_id field is empty. If that is the case then don’t create a new membership but just update it’s user_id field (with current_user.id) and return with a msg that a creation of new association is successful (as if its a new membership record).

How do I do this? Do I need to use any callbacks? How do I use callbacks in this case?
Any help is appreciated.

Thanks,

Atarangp

Answer 1

This is how I solved it.
In model membership, added a method membership_exists and called it from membership’s create
action.

class Membership < ActiveRecord::Base
  belongs_to :school
  belongs_to :user
  #validations, etc.

  def Membership.membership_exists(membernumber, school_id)
     membership = Membership.where(:membernumber =>  membernumber, :school_id => school_id, :user_id => nil).first
     if membership.nil?
        return false
     else
        membership.update_attribute :user_id, user_id
        return true
     end
  end
end

And in Membership controller (in create action)

  def create
    @membership = Membership.new(params[:membership])
    @membership.user_id = current_user.id

    @flag = Membership.membership_exists(@membership.membernumber,@membership.school_id)
    if @flag == true
      flash[:notice] = "Membership creation is successful"
      redirect_to @membership
      return
    end

    respond_to do |format|
      if @membership.save
        format.html { redirect_to @membership, notice: 'Membership was successfully created.' }
        format.json { render json: @membership, status: :created, location: @membership }
      else
        format.html { render action: "new" }
        format.json { render json: @membership.errors, status: :unprocessable_entity }
      end
    end
end

This works. But is it a good way to do it?

Thanks,
Atarangp.