Firebase Database Querying: return latest added object in which the child has a value

Question

I'm building an Android application in which the user can track its weight and progress by inserting their weight (optional) AND/OR upload a picture (optional).

{
  "users" : {
    "5aHvYy5wTIVAAgdOEso0wr2woHS2" : {
      "firstName" : "Justin",
      "logs" : [ {
        "date" : "16/05/2018",
        "progressPicture" : "http://www.google.com/example.jpg",
        "weight" : 82.1
      }, {
        "date" : "17/05/2018",
        "progressPicture" : "http://www.google.com/example.jpg"
      }, {
        "date" : "18/05/2018",
        "weight" : 80.3
      } ]
    }
}

I have managed to get the latest log by ordering by key and limiting the result to 1, using the following code.

firebaseDatabase.getReference(USER_REFERENCE).child(firebaseAuth.currentUser?.uid).child(LOG_REFERENCE).orderByKey().limitToLast(1).

As can be seen from my JSON, a log doesn't necessarily have to have a weight value.

MY QUESTION: How can I adjust my query so that I'll retrieve my latest log (so 1 log only based on key) where there is a value for weight?

Firebase Database queries can only order/filter on a single property. In many cases it is possible to combine the values you want to filter on into a single (synthetic) property. E.g. `"hasWeight_date": "true_20180518"`. For an example of this and other approaches, see my answer here: http://stackoverflow.com/questions/26700924/query-based-on-multiple-where-clauses-in-firebase — Frank van Puffelen, May 17 '18 at 14:00

score 1 · Answer 1 · answered May 17 '18 at 11:14

1

You can add new entry called weight_log,which will be updated once new weight is recorded , you can do it easily with firebase functions that will be triggered on each /users/{userId}/weight_log/{iterationID} create event

Then you can use limitToLast(1) on the new path

Generally it is good practice to flattening your data structure

answered May 17 '18 at 11:14

yarin

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this is not an answer, please answer the question properly – May 17 '18 at 12:27
1

@Eminem To me this sounds like a valid answer. What part of it won't work in your opinion? – Frank van Puffelen May 17 '18 at 14:01
1

he can add some code,I think that would help the user more – May 17 '18 at 14:21

score 0 · Answer 2 · answered May 17 '18 at 07:47

From reading the wiki you can only filter the data and check if there's a value for weight by adding a ValueEventListener() which will return a list of all the list where you have to loop through it and get you value

https://firebase.google.com/docs/database/android/lists-of-data#filtering_data

Firebase Database Querying: return latest added object in which the child has a value

2 Answers2