Querying below AutoID's in Firebase

Question

Results
- auto generated ID
  - auto generated ID
       value1: abc
       value2: def

I want to be able to query where "value2" is equal to some specific value. I start with a reference:

let ref = FIRDatabase.database().reference().child("Results")

Since I don't know the auto generated ID's in order to supply a path do I need to get them first in order to get down to value where I can use .queryEqualToValue? If so am I not just grabbing every record to look for a value versus using some kind of index to grab only those where value2 is equal to a value?

In the end I would like a query that returns all "records" where value2 is equal to a certain value. It feels like I need to iterate through every record to do that. I feel like I am missing something here.

Update:

I've tried:

self.ref.queryOrderedByKey().queryEqual(toValue: "def", childKey: "value2").observeSingleEvent(of: .value, with: {(snapshot) in
            print(snapshot) })

This crashes with an error I give in comments below.

I've tried:

self.ref.queryOrdered(byChild: "value2").queryEqual(toValue: "def").observeSingleEvent(of: .childAdded, with: {(snapshot) in

This never executes the closure. If I change the observer to ".value"it returns null.

If I do this:

self.ref.queryOrdered(byChild: "value2").observeSingleEvent(of: .childAdded, with: {(snapshot) in

It will actually sort the data properly. It won't sort properly with ".value" Regardless, adding queryEqual then doesn't work as described above.

Answer 1

Firebase Database queries properties one level deeper than the location where you run them. They cannot contain a dynamic path under that.

Since you're querying from /Results, you can order by/filter on properties under /Results/$id/PropertyName.

To allow ordering/filtering of all items on properties under /Results/$id1/$id2/PropertyName you will need to change/augment your data structure. For example:

ResultValues
   -auto_generated_ID1_auto_generated_ID2_value1
       value: abc
       path: "auto generated ID/auto generated ID"
   -auto_generated_ID1_auto_generated_ID2_value2
       value: def
       path: "auto generated ID/auto generated ID"

Now you can query with:

ref.child("ResultValues")
   .queryOrderedByChild("value")
   .queryEqual(toValue: "def")
   .observeSingleEvent(of: .value, with: {(snapshot) in
            print(snapshot) })