Pfthb

Im trying to return the length of a list of documents with this function:

Future totalLikes(postID) async 
 var respectsQuery = Firestore.instance
 .collection('respects')
 .where('postID', isEqualTo: postID);
 respectsQuery.getDocuments().then((data) 
 var totalEquals = data.documents.length;
 return totalEquals;
 );
 

I'm initialize this in the void init state (with another function call:

void initState() 

 totalLikes(postID).then((result) 
 setState(() 
 _totalRespects = result;
 );
 );


 

However, when this runs, it initially returns a null value since it doesn't have time to to fully complete. I have tried to out an "await" before the Firestore call within the Future function but get the compile error of "Await only futures."

Can anyone help me understand how I can wait for this function to fully return a non-null value before setting the state of "_totalRespsects"?

Thanks!

I think you're looking for this:

Future totalLikes(postID) async 
 var respectsQuery = Firestore.instance
 .collection('respects')
 .where('postID', isEqualTo: postID);
 var querySnapshot = await respectsQuery.getDocuments();
 var totalEquals = querySnapshot.documents.length;
 return totalEquals;

Note that this loads all documents, just to determine the number of documents, which is incredibly wasteful (especially as you get more documents). Consider keeping a document where you maintain the count as a field, so that you only have to read a single document to get the count. See aggregation queries and distributed counters in the Firestore documentation.