title: Magento Force user to buy related product
body: <p>I am developing a website in Magento and I need to develop the following functionality.</p>
  
  <p>1) Products are added in the back end as devices and services.</p>
  
  <p>2) All the Products are displayed on the homepage together.</p>
  
  <p>3) If a user buys a products (device) then he will also require to buy another product related to that product (service).</p>
  
  <p>4) In short he can't proceed without purchasing service product.</p>
  
  <p>5) So if user buys Device product then he will compulsory will have to select one of the service products available for that product.</p>
  
  <p>6) Also a user can't buy the service product only.. To buy the service product he will have to also purchase the device product.</p>
  
  <p>This is what I am trying to develop but have got stuck on this point.</p>
  
  <p>I have tried the best way to explain my problem. Any help, ideas will be welcome..</p>
  
  <p>Thanks.</p>