is there any mongo db query to only fetch searching elements all the nested elements-CodePudding

my data structure is

[
  {
    "item": "journal",
    "qty": 25,
    "status": "A",
    "weekNumber": 1,
    "sortOrder": 1,
    "label": 1,
    "numberOfPossibleDays": 1,
    "editable": 1,
    "selectedDate": 1,
    "deliveryDays": 1,
    "products": [
      {
        "key": "item-one",
        "name": "item one",
        "tags": [
          "v",
          "b"
        ]
      },
      {
        "key": "item-two",
        "name": "item-two",
        "tags": [
          "a",
          "c",
          "d"
        ]
      },
      {
        "_id": 3,
        "name": "item-three",
        "tags": [
          "g"
        ]
      }
    ]
  },
  {
    "item": "notebook",
    "status": "b",
    "qty": 1,
    "weekNumber": 1,
    "sortOrder": 1,
    "label": 1,
    "numberOfPossibleDays": 1,
    "editable": 1,
    "selectedDate": 1,
    "deliveryDays": 1,
    "products": [
      {
        "key": "item-four",
        "name": "item four",
        "tags": [
          "a",
          "o"
        ]
      },
      {
        "key": "item-five",
        "name": "item-five",
        "tags": [
          "s",
          "a",
          "b"
        ]
      }
    ]
  }
]

and I want to find all the elements with tags 'a', so the expected response should be like

[
  {
    "_id": ObjectId("5a934e000102030405000000"),
    "deliveryDays": 1,
    "editable": 1,
    "item": "journal",
    "label": 1,
    "numberOfPossibleDays": 1,
    "products": [
      {
        "key": "item-one",
        "name": "item one",
        "tags": [
          "v",
          "b"
        ]
      }
    ],
    "qty": 25,
    "selectedDate": 1,
    "sortOrder": 1,
    "status": "A",
    "weekNumber": 1
  },
  {
    "_id": ObjectId("5a934e000102030405000001"),
    "deliveryDays": 1,
    "editable": 1,
    "item": "notebook",
    "label": 1,
    "numberOfPossibleDays": 1,
    "products": [],
    "qty": 1,
    "selectedDate": 1,
    "sortOrder": 1,
    "status": "b",
    "weekNumber": 1
  }
]

I can use the $filter operator to filter the element containing "b" in the tags array for the products array in the projection. i think it's very lengthy code. is there any way that mongoDB send all the values instead of writing every element in the query like ?

db.collection.find({
  "products.tags": "b"
},
{
  item: 1,
  qty: 1,
  "status": 1,
  "weekNumber": 1,
  "sortOrder": 1,
  "label": 1,
  "numberOfPossibleDays": 1,
  "editable": 1,
  "selectedDate": 1,
  "deliveryDays": 1,
  products: {
    $filter: {
      input: "$products",
      cond: {
        $in: [
          "v",
          "$$this.tags"
        ]
      }
    }
  }
})

CodePudding user response：

you could maybe use an aggreation as follows :

db.collection.aggregate([
  {
    $match: {
      "products.tags": "b"
    },
    
  },
  {
    $set: {
      products: {
        $filter: {
          input: "$products",
          cond: {
            $in: [
              "v",
              "$$this.tags"
            ]
          }
        }
      }
    }
  }
])

It will give the same results as before, but you won't have to write every field with field : 1 to keep them.