title: Rails query with attributes on two tables
body: <p>How do I write a find(:all) query in rails (v2.3.5) that has parameters both in the model I am running the 'find' on, and in another table?    e.g.  I am trying to search for 'posts'  by 'author' and 'tag'.  Author is an attribute of post, whereas tag is associated with it through another table.  I can get the tags by including ':joins => :tags',  and adding conditions but then I  can't figure out how to add in conditions to specify a given user.   </p>
  
  <p>Also any suggestions on a good reference for rails query syntax  would be great.   I can't seem to figure out enough from the v2.3 Rails Guide on queries.   Thanks!</p>