Retrieve specific data by date with Angular and moment.js

Question

I have a database structure like these (Firebase):

+ statistics
|-+ 2016
| |-+ 9
|   |-+ hours: 0
|-+ 2017
  |-+ 6
  | |-+ hours: 0
  |-+ 7
  |-+ 8
  |-+ 9 

The parents are years, the childs are months (9 for example is September) It´s easy to create a list to show the sum of all hours from one year. For example from 2017. But what if I want to show the sum of all hours from Steptember 2016 to September 2017?

I'm planning an application where this would be important for this app a year begins at September and ends at September next year. So I need the data from 2016->9 to 2017->9 How can I handle this?

I'm using Ionic3 / Angular2, Firebase and moment.js for date handling.

More concrete:

I want to get data like this: Give me all 'hours'-values from September 2016 to September 2017 and build these to an array

Answer 1

I'll assume that your using the Realtime Database; however, I'm sure the Firestore design/implementation is similar.

You may want to consider an alternate structure like so:

statistics: {
  unix_ts_for_sept_2016: {
    unix_ts: unix_ts_for_sept_2016
    hours:
  },
  unix_ts_for_oct_2016: {
    unix_ts: unix_ts_for_oct_2016
    hours:
  },
  unix_ts_for_nov_2016: {
    unix_ts: unix_ts_for_nov_2016
    hours:
  }
  [,...]
}

The timestamp as a key allows you to get/set any single month, while the timestamp as a child value allows you to perform range queries.

const path_to_statistics = 'statistics/';
const hours_field_name = 'hours';
const ts_field_name = 'unix_ts';

// Update the hours for a given month/yr in 'MM-DDDD' format
var update_hours = function(mm_dash_yyyy, delta_hours) {
  const unix_ts = moment(mm_dash_yyyy, 'MM-YYYY').valueOf();
  const path = path_to_statistics + unix_ts + '/' + hours_field_name;
  const ref = firebase.database().ref(path);
  var deferred = $q.defer();

  ref.transaction(function(current) {
    if (current !== null) { return current + delta_hours; }
    return current;
  }, function(error) {
    if (error) { deferred.reject(error); }
    else { deferred.resolve(); }
  });

  return deferred.promise;
};

// Returns sum of hours in a given date range.
var get_hours_in_range = function(start_mm_dash_yyyy, end_mm_dash_yyyy) {
  const start_ts = moment(start_mm_dash_yyyy, 'MM-YYYY').valueOf();
  const end_ts = moment(end_mm_dash_yyyy, 'MM-YYYY').valueOf();
  const ref = firebase.database().ref(path_to_statistics);
  const query = ref.orderByChild(ts_field_name).startAt(start_ts).endAt(end_ts);
  var deferred = $q.defer();

  query.once('value').then(function(snap) {
    var hours = 0;
    snap.forEach(function(child_snap) {
      hours += child_snap.val()[hours_field_name];
    });
    deferred.resolve(hours);
  }).catch(function(error) { deferred.reject(error); });

  return deferred.promise;
};

//usage
update_hours('09-2016', 10).then(function() {
  console.log('updated hours.');
}).catch(function(error) { console.error(error); })

get_hours_in_range('09-2016', '10-2016').then(function(hours) {
  console.log(hours);
}).catch(function(error) { console.error(error); });