title: Converting a single Tenant Application to a multitenant one using Apartment gem
body: <p>I've built a single tenant rails application with all core features ready to ship. But I now want to make it multi-tenant using the <a href="https://github.com/influitive/apartment" rel="nofollow noreferrer">apartment gem</a>. Most tutorials I've found all show how to start from scratch. But I find no pointers on how to convert an existing project to have multi-tenancy built in. From my research I found that all models need a tenant ID added in the migration. How do I add this to all existing models easily? Does installing the gem and running the generator suffice? I'm running a <code>rails 5</code> API application with close to 30 models and using <code>graphql</code> ruby in an <code>Ubuntu 18.04</code> environment.</p>
  
  <p>Any ideas on how to do this?</p>