title: Emulating join behavior with Rails and Mongoid
body: <p>Just wanted to ask some advice when building a database with mongodb, I have been reading a lot that if you have a database with a lot of joins it's better to go with say postgresql.</p>
  
  <p>So if I wanted flexibility and needed my data to join multiple times, should I go with Postgresql?  I know mongodb has fast reads / writes but needs to query multiple times to emulate joins.  So when would this become a performance hit?  Does mongodb limit your ability to create new complex relationships on your data that did not previously exist?</p>
  
  <p>I guess the attractiveness of mongodb is its javascript syntax and similarity to json :)</p>