从 firebase firestore 检索后，如何根据字段对 firestore 集合文档进行排序

Question

Assume that I have a Firestore collection with the name users .

Also assume that each document of the collection users have the following fields in each document:

name
surname
year

When fetching the data from Firebase Firestore, the following code can be run:

Query myData = FirebaseFirestore.instance
          .collection('users')
          .orderBy('name');

And this code piece sorts the documents based on the name field in each document when retrieving it.

Keeping in mind that you are charged based on the number of reads when fetching data from Firestore, I wonder how I can re-sort the retrieved data from Firestore without increasing the number of read operations for my account ?

For instance, the above code piece sorts the documents based on the name field. How can I sort the documents based on surname or year fields after that?

Is running the same piece of code by changing orderBy('name') with -eg- orderBy('surname') an option? Or does it increase my number of reads?

Answer 1

If you perform a second query with a different orderBy field, you will incur the cost of reading all the documents again.

It would be far more efficient in terms of cost and speed to write code to sort the documents again after you have them in memory from the first query.