通过聚合将数据从一个 mongo 文档添加到不同的 mongo 文档

Question

This situation is a little confusing, so I will do my best to explain with this example.

Lets say I have an object (mongoDb document) that looks like:

{
  _id: 0989sd7f987123bnkmsdfv,
  name: 'Item-004',
  itemId: 004,
  date: 10/11/1960,
  color: 'green',
  quantity: 21,
  listOfItems: [
   {
     itemId: 001, 
     itemName: 'Item-001',
     color: 'blue'
   },
   {
     itemId: 002, 
     itemName: 'Item-002',
     color: 'orange'
   },
   {
     itemId: 003, 
     itemName: 'Item-003',
     color: 'purple'
   }
  ]
}

This is an object in the items collection. listOfItems is an array that is comprised of other items in the same collection, but the problem is that the array doesn't have enough details about the items. Every Item has a name , date , itemId , color , quantity , and listOfItems array. How can I write an aggregation query to add those fields to the item in the listOfItems array.

end result/ goal:

{
_id: 0989sd7f987123bnkmsdfv,
  name: 'Item-004',
  itemId: 004,
  date: 10/11/1960,
  color: 'green',
  quantity: 21,
  listOfItems: [
   { 
     itemId: 001, 
     name: 'Item-001',
     date: 12/12/1996,
     color: 'blue',
     quantity: 33,
   },
   {
     itemId: 002, 
     name: 'Item-002',
     date: 08/11/2021,
     color: 'orange',
     quantity: 1045,
   },
   {
     itemId: 003, 
     name: 'Item-003',
     date: 03/30/1998
     color: 'purple'
     quantity: 9,
   }
  ]
}

Answer 1

Try this:

db.collection.aggregate([
  {
    "$unwind": "$listOfItems"
  },
  {
    "$lookup": {
      "from": "collection",
      "localField": "listOfItems.itemId",
      "foreignField": "itemId",
      "as": "listOfItems"
    }
  },
  {
    "$unwind": "$listOfItems"
  },
  {
    "$unset": "listOfItems.listOfItems"
  },
  {
    "$group": {
      "_id": {
        "_id": "$_id",
        name: "$name",
        itemId: "$itemId",
        date: "$date",
        color: "$color",
        quantity: "$quantity"
      },
      "listOfItems": {
        "$push": "$listOfItems"
      }
    }
  },
  {
    "$replaceRoot": {
      "newRoot": {
        "$mergeObjects": [
          "$_id",
          {
            listOfItems: "$listOfItems"
          }
        ]
      }
    }
  },
  {
    "$merge": {
      "into": "collection",
      "on": "_id",
      "whenMatched": "replace",
      
    }
  }
])

Here's the corresponding playground link .