Setting an 'orderBy' in a StructuredQuery using Firestore REST API

Question

first post so any tips would be appreciated. I am trying to set an 'orderBy' in a StructuredQuery using the REST api to firestore. Its also helpful to note that my query does work if the orderBy field is not used.

My query looks like this:

var collection = "testing";
var Query = {        //body of the http request
  "structuredQuery": {
    "from": {
      "collectionId":collection,
      "allDescendants":true
    },
    "orderBy": {
      "field": {
        "fieldPath" : "uploaded"
      },
      "direction" : "DESCENDING"
    },
    "limit": 1
  },
  "newTransaction": {}
}
var urlPOST = "https://firestore.googleapis.com/v1beta1/projects/"+id+"/databases/"+database+"/documents:runQuery?key="+key;
var optPOST = {                //http header
  'method' : 'post',
  'contentType' : 'application/json',
  'muteHttpExceptions': true,
  'payload': JSON.stringify(Query)
};
var response = UrlFetchApp.fetch(urlPOST, optPOST);

from this request i get:

"error": {
  "code": 400,
  "message": "The query requires a COLLECTION_GROUP_DESC index for collection testing and field uploaded. You can create it here: https://console.firebase.google.com/project/<mydatabase>/database/firestore/indexes/single-field ",
    "status": "FAILED_PRECONDITION"
}

Googles firestore API doco says that it should give me a link to create the required index, but the link returned here does not do that, instead it returns me to the overview page.

A little more detail about what I'm trying to do: I want to be able to get the last uploaded document from the database. i do this by having a field 'uploaded' which is simply a TimeStamp field (uploaded via a python script using the firestore_admin library calling firestore.SERVER_TIMESTAMP)

Let me know if any more information is required

Thanks in Advance

Answer 1

TL;DR - the allDescendants field doesn't do anything useful right now and you shouldn't use it. It was put into the protocol in anticipation of a feature called "Collection Group Queries" which has not yet launched.

---

As you can see, each Firestore query has a parent and a target collectionId, in addition to other constraint clauses.

In your case the parent is /projects/$YOUR_PROJECT/datbases/(default)/, so basically the root of your DB. The collectionId is the name of the collection that you're searching for documents, which you have specified as testing.

When allDescendants is false then it will only search for collections with that name that are a direct descendant of the parent. In this case that means it will search the collection /testing.

If allDescendants is set to true the search woudl cover any collection named "testing" at any depth under the parent. So not only /testing but also something like /widgets/foo/testing However fulfilling this query requires what we call a "collection group" index, as indicated in the error message. Right now there is no way for you to create an index like that, which is why I said above that this parameter is basically useless.

As we've stated on some other forums, we do intend to release this type of query in the future in which case the allDescendants parameter would be more useful.