def create
      if @membershipable.present?
        @membership = @membershipable.memberships.new(membership_params)
      else
        @membership = Membership.new(membership_params)
      end

      @membership.save
      respond_with(@membership, location: location)
    end
def create
      if @membershipable.present?
        @membership = @membershipable.memberships.new(membership_params)
      else
        @membership = Membership.new(membership_params)
      end

      @membership.save
      respond_with(@membership, location: location)
    end
POST /memberships