title: Swift firestore get more than one collection's documents at same time?
body: <p>How to get more than one collection's documents data? </p>
  
  <p>my firebase tree is like :
   "tahminler/'useruid'/'date as like (5.3.2018 or 6.3.2018)'/'documentID'/'Document data'"</p>
  
  <p>so how to take all dates collection's documents in a function 
  and here is my firebase firestore console:  <a href="https://i.stack.imgur.com/Ia860.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Ia860.png" alt="enter image description here"></a></p>