forgeplus/app/controllers/api/pm/issue_links_controller.rb

class Api::Pm::IssueLinksController <  Api::Pm::BaseController
  before_action :load_project
  before_action :load_issue
  def index
    @links = @issue.pm_links.where(be_linkable_type: 'Issue')
  end

  def create
    @link = @issue.pm_links.find_or_create_by(be_linkable_type: 'Issue', be_linkable_id: params[:link_id])
    data = {
      data: {
        id: @link.id,
        issue_id: @link.linkable_id,
        linked_issue_id: @link.be_linkable_id
      }
    }
    render_ok(data)
  end

  def destroy
    @link = @issue.pm_links.find params[:id]
    @link.destroy
    render_ok
  end
end