Grupuj rekordy według miesiąca i policz je - Mongoose, nodeJs, mongoDb

Oto zapytanie agregujące, które zwraca oczekiwany wynik. Kilka przykładowych dokumentów:

[
  { created_at: "2020-04-04T17:02:07.832Z", productId: 1 },
  { created_at: "2020-02-01T17:02:07.832Z", productId: 1 },
  { created_at: "2020-02-19T17:02:07.832Z", productId: 1 },
  { created_at: "2019-05-22T17:02:07.832Z", productId: 1 },
  { created_at: "2020-01-15T17:02:07.832Z", productId: 1 },
  { created_at: "2020-01-30T17:02:07.832Z", productId: 2 },  // not selected
  { created_at: "2019-03-15T17:02:07.832Z", productId: 1 }   // not selected
]

Zmienne wejściowe i agregacja:

let TODAY = "2020-04-06T23:59:59"
let YEAR_BEFORE = "2019-04-07T00:00:00"
let req = { params: { productId: 1 } }
const monthsArray = [ 'January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December' ]

db.sales.aggregate( [
  { 
      $match: { 
          productId: req.params.productId, 
          created_at: { $gte: YEAR_BEFORE, $lte: TODAY }
      }
  },
  { 
      $group: {
          _id: { "year_month": { $substrCP: [ "$created_at", 0, 7 ] } }, 
          count: { $sum: 1 }
      } 
  },
  {
      $sort: { "_id.year_month": 1 }
  },
  { 
      $project: { 
          _id: 0, 
          count: 1, 
          month_year: { 
              $concat: [ 
                 { $arrayElemAt: [ monthsArray, { $subtract: [ { $toInt: { $substrCP: [ "$_id.year_month", 5, 2 ] } }, 1 ] } ] },
                 "-", 
                 { $substrCP: [ "$_id.year_month", 0, 4 ] }
              ] 
          }
      } 
  },
  { 
      $group: { 
          _id: null, 
          data: { $push: { k: "$month_year", v: "$count" } }
      } 
  },
  {
      $project: { 
          data: { $arrayToObject: "$data" }, 
          _id: 0 
      } 
  }
] )

Wynik:

{
        "data" : {
                "May-2019" : 1,
                "January-2020" : 1,
                "February-2020" : 2,
                "April-2020" : 1
        }
}

Oto zaktualizowana agregacja .

Zwróć uwagę na następujące zmiany:(1) nowe stałe PIERWSZY_MIESIĄC i OSTATNI_MIESIĄC, (2) zmieniono monthsArray nazwa zmiennej do MONTHS_ARRAY, (3) dodano 3 nowe etapy potoku.

Pierwsze dwa etapy potoku (nowe) tworzą szablon ze wszystkimi miesiącami (obejmujący zakres dat od i do wejścia). Trzeci nowy etap łączy szablon z danymi wyjściowymi uzyskanymi z poprzedniej agregacji.

const FIRST_MONTH = 1
const LAST_MONTH = 12
const MONTHS_ARRAY = [ 'January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December' ]

let TODAY = "2020-04-06T23:59:59"
let YEAR_BEFORE = "2019-04-07T00:00:00"

db.sales.aggregate( [
  { 
      $match: { 
          productId: req.params.productId, 
          created_at: { $gte: YEAR_BEFORE, $lte: TODAY }
      }
  },
  { 
      $group: {
          _id: { "year_month": { $substrCP: [ "$created_at", 0, 7 ] } }, 
          count: { $sum: 1 }
      } 
  },
  {
      $sort: { "_id.year_month": 1 }
  },
  { 
      $project: { 
          _id: 0, 
          count: 1, 
          month_year: { 
              $concat: [ 
                 { $arrayElemAt: [ monthsArray, { $subtract: [ { $toInt: { $substrCP: [ "$_id.year_month", 5, 2 ] } }, 1 ] } ] },
                 "-", 
                 { $substrCP: [ "$_id.year_month", 0, 4 ] }
              ] 
          }
      } 
  },
  { 
      $group: { 
          _id: null, 
          data: { $push: { k: "$month_year", v: "$count" } }
      } 
  },
  { 
      $addFields: { 
          start_year: { $substrCP: [ YEAR_BEFORE, 0, 4 ] }, 
          end_year: { $substrCP: [ TODAY, 0, 4 ] },
          months1: { $range: [ { $toInt: { $substrCP: [ YEAR_BEFORE, 5, 2 ] } }, { $add: [ LAST_MONTH, 1 ] } ] },
          months2: { $range: [ FIRST_MONTH, { $add: [ { $toInt: { $substrCP: [ TODAY, 5, 2 ] } }, 1 ] } ] }
      } 
  },
  { 
      $addFields: { 
          template_data: { 
              $concatArrays: [ 
                  { $map: { 
                       input: "$months1", as: "m1",
                       in: {
                           count: 0,
                           month_year: { 
                               $concat: [ { $arrayElemAt: [ MONTHS_ARRAY, { $subtract: [ "$$m1", 1 ] } ] }, "-",  "$start_year" ] 
                           }                                            
                       }
                  } }, 
                  { $map: { 
                       input: "$months2", as: "m2",
                       in: {
                           count: 0,
                           month_year: { 
                               $concat: [ { $arrayElemAt: [ MONTHS_ARRAY, { $subtract: [ "$$m2", 1 ] } ] }, "-",  "$end_year" ] 
                           }                                            
                       }
                  } }
              ] 
         }
      }
  },
  { 
      $addFields: { 
          data: { 
             $map: { 
                 input: "$template_data", as: "t",
                 in: {   
                     k: "$$t.month_year",
                     v: { 
                         $reduce: { 
                             input: "$data", initialValue: 0, 
                             in: {
                                 $cond: [ { $eq: [ "$$t.month_year", "$$this.k"] },
                                              { $add: [ "$$this.v", "$$value" ] },
                                              { $add: [ 0, "$$value" ] }
                                 ]
                             }
                         } 
                     }
                 }
              }
          }
      }
  },
  {
      $project: { 
          data: { $arrayToObject: "$data" }, 
          _id: 0 
      } 
  }
] )

Wynik:

{
        "data" : {
                "April-2019" : 0,
                "May-2019" : 1,
                "June-2019" : 0,
                "July-2019" : 0,
                "August-2019" : 0,
                "September-2019" : 0,
                "October-2019" : 0,
                "November-2019" : 0,
                "December-2019" : 0,
                "January-2020" : 1,
                "February-2020" : 2,
                "March-2020" : 0,
                "April-2020" : 1
        }
}