Firestore query orderBy not working?

问题

FutureBuilder with a Firestore query on a field of Type timestamp comes back with no data in snapshot. However, the same query without the orderBy works just fine.
What am I missing ? Thanks for the help.

// Working code
future: Firestore.instance.collection('messages').where('toid',isEqualTo: _emailID).getDocuments(),
builder: (context, snapshot) ...

// Not Working - returns to if(!snapshot.hasData)
future: Firestore.instance.collection('messages').where('toid',isEqualTo: _emailID).orderBy('_timeStampUTC', descending: true).getDocuments(),
builder: (context, snapshot) ...

回答1:

I think you are missing a ' here '_timeStampUTC, so it should be:

 orderBy('_timeStampUTC', descending: true)

EDIT:

Also, you need to be sure to create an index for toid and other for _timeStampUTC, this is done when you try to order by a property that is not in you the where of the query.

回答2:

yep, it's just missing an index. if you're using firestore.indexes.json then add this:

{
  "collectionId": "messages",
  "fields": [
    { "fieldPath": "toid", "mode": "ASCENDING" },
    { "fieldPath": "_timeStampUTC", "mode": "DESCENDING" }
  ]
}

回答3:

Use @ServerTimestamp annotation for _timeStampUTC and try to to orderBy query

To make Firestore automatically generate Timestamp values when we upload data to the database, we must use the annotation @ServerTimestamp and set the value to null.

来源：https://stackoverflow.com/questions/51434167/firestore-query-orderby-not-working