Gruppera poster efter månad och räkna dem - Mongoose, nodeJs, mongoDb

Här är en aggregeringsfråga som returnerar det förväntade resultatet. Några exempeldokument:

[
  { 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
]

Indatavariablerna och aggregeringen:

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 
      } 
  }
] )

Utdata:

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

Här är den uppdaterade sammanställningen .

Observera följande ändringar:(1) nya konstanter FIRST_MONTH och LAST_MONTH, (2) ändrade monthsArray variabelnamn till MONTHS_ARRAY, (3) lade till 3 nya pipelinesteg.

De två första stegen i pipeline (ny) bygger en mall med alla månader (som täcker från och till inmatningsdatumintervallet). Det tredje nya steget slår samman mallen med utdata som härrör från den tidigare aggregeringen.

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 
      } 
  }
] )

Utdata:

{
        "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
        }
}