How to filter records by dateTime using firebase realtime database - firebase

Question

In my firebase Realtime Database, every document saved has a datetime variable.
Example, dateTime:"2021-04-11T17:32:50.833523"
I have the following URL which fetches all documents. However, I now want to fetch only today's documents. I know that there are two options to achieving this. First one is to fetch all the documents from DB and then filter only today's records. Second option is to tweak the URL and put the filter while fetching records from the DB.
First I would like to know which approach yields faster results?
If it's the second approach, then I would like to know how to achieve it.
Here's the function I am using:
Future<void> fetchAllOrders() async {
final url ='https://fhgi-92211.firebaseio.com/orders.json?auth=$authToken';
}

Answer 1

According to the docs, something like this should work:
'https://fhgi-92211.firebaseio.com/orders.json?auth=$authToken&orderBy="dateTime"&startAt="2021-04-11"'
https://firebase.google.com/docs/database/rest/retrieve-data

Answer 2

Best solution - is n°2 : using & tweaking your URL - to do so I suggest :
First, tweaking your model by adding your date data in a simpler 2021-04-11 kinda of format
It will allow you much easier filtering
You can do so like this before writing your data to your RealTime Database :
import 'package:intl/intl.dart';
DateTime today = DateTime.now();
String simpleFormatToday = DateFormat('yyyy-MM-dd').format(today);
// returns a simple 2021-04-11 format of today's date
If your really need for some reason the full dateTime value you can write both dateTime:"2021-04-11T17:32:50.833523" & simpleDate:"$simpleFormatToday" to your object
Next,
To retrieve your data - use your function & tweak your URL to use Range Querying to retrieve only documents having simpleDate value equal to today - like so :
Future<void> fetchAllOrders() async {
final url ='https://fhgi-92211.firebaseio.com/orders.json?auth=$authToken&orderBy="simpleDate"&equalTo="$simpleFormatToday"';
}

Answer 3

First Approach
It will be useful if you want to get all the data and need to filter the dates several times from user input.
For example: If you have 100 records that you fetched using first approach i.e all you have is 100 records in your db and now user will make some filter on fetched records like getting 20-30 then 40-79, something like that. In this case making query using second approach wont be appropriate because of two reasons
Querying everytime on firebase would count read/write towards billing.
Managing data locally is more fast and reliable rather than making request to network frequently.
Second Approach
It will be useful in areas where you have to show specific time interval records in the one go and that's it, after fetching the records you dont need more of them to pull out from DB.
The Query will mainly revolve around what you want
equalsTo : It will give you only those records which will have exact date that you have passed as params.
orderBy : It will only work with equals to and will give you dates on bases of applied sorted filter (ex: by createdAt)
Future<void> fetchAllOrders() async {
//It will get today's date
var todaysDate = DateTime.now();
//From today's 12AM
var filterStartDate = DateTime(todaysDate.year,todaysDate.month,todaysDate.day,0,0,0);
//To second days' 11:59PM
var filterEndDate = DateTime(todaysDate.year,todaysDate.month,todaysDate.day,23,59,59);
final url ='https://fhgi-92211.firebaseio.com/orders.json?auth=$authToken&startAt="${filterStartDate.toIso8601String()}&endAt="${filterEndDate.toIso8601String()}';
}