How Can I Retrieve these data from Firestore?

Question

I want to get data from the map in firestore and display it in the List ordered by date?

Answer 1

That seems to be a single document. You would have to fetch the whole document if you are just going to have a new map for each date. Then sort it yourself using dart.

FirebaseFirestore.instance
    .collection('BMI')
    .doc('docID')
    .get()
    .then((DocumentSnapshot documentSnapshot) {
      if (documentSnapshot.exists) {
        print('Document exists on the database');
        // sort here

        List myList = documentSnapshot.data!.data().entries.map((entry) => entry).toList();
        print(myList);
        // sorting the list
        print(myList.sort((a, b) => a.date.compareTo(b.date)))
      }
    });

You can read more about sorting lists here. If you need to limit number of entries to be fetched then you would have create a dedicated documents for each entry.