title: Firebase Cloud Firestore Many to Many Relationships
body: <p>How to structure and query data from Firebase Cloud Firestore in a many to many relationship?</p>
  
  <p>I have Companies and Contractors. A Contractor can work for more than one Company and a Company can have multiple Contractors. This is a straightforward many to many relationship. I want to be able to answer the questions about Companies and Contractors:</p>
  
  <p>Given a Company, who are the current Contractors.
  Given a Contractor what Companies are they working for.
  What is the right way for structuring the data within Cloud Firestore?</p>