how to fetch the document if subdocument id is known

user_16398417 0
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I Wanted to fetch the document given that we are having the subdocument id .Here lets say we have multiple categories and every category is having subcategory and service type so if i have the subcategory id then how can we fetch the subcategory similarly also if i am having the id of one of service type then how can i fetch the servicetype.

[
  {
    "_id": {
      "$oid": "60e958b8f907544930c7d045"
    },
    "trans": {
      "en": {
        "name": "Digital Marketing",
        "description": "Digital Marketing"
      },
      "fr": {
        "name": "Digital Marketing",
        "description": "Digital Marketing"
      }
    },
    "subcategories": [
      {
        "trans": {
          "en": {
            "name": "Social Media Advertising",
            "description": "Social Media Advertising"
          }
        },
        "$oid": "60e95a466f25a34248698a33",
        "service_type": [
          {
            "trans": {
              "en": {
                "name": "_service1",
                "description": "_service1"
              }
            },
            "_id": {
              "$oid": "60e95a466f25a34248698a30"
            }
          },
          {
            "trans": {
              "en": {
                "name": "Strategy and Planning",
                "description": "Strategy and Planning"
              }
            },
            "_id": {
              "$oid": "60e95a466f25a34248698a31"
            }
          },
          {
            "trans": {
              "en": {
                "name": "AD SETUP AND MANAGEMENT",
                "description": "AD SETUP AND MANAGEMENT"
              }
            },
            "_id": {
              "$oid": "60e95a466f25a34248698a32"
            }
          }
        ]
      },
      {
        "trans": {
          "en": {
            "name": "Social Media Marketing",
            "description": "Social Media Marketing"
          }
        },
        "$oid": "60e95a466f25a34248698a33",
        "service_type": [
          {
            "trans": {
              "en": {
                "name": "_serviceA",
                "description": "_serviceA"
              }
            },
            "_id": {
              "$oid": "60e95a466f25a34248678a78"
            }
          },
          {
            "trans": {
              "en": {
                "name": "Strategy 1",
                "description": "Strategy 1"
              }
            },
            "_id": {
              "$oid": "60e95a466f25a34248222a31"
            }
          },
          {
            "trans": {
              "en": {
                "name": "AD 2",
                "description": "AD 2"
              }
            },
            "_id": {
              "$oid": "51e85a466f25a34345498a32"
            }
          }
        ]
      }
    ]
  }
]
//similarly  we are having multiple categories then how can we fetch the subcategory with given `subcategory_id` where the subcategory is an array of object

Query tried

 const r = await client
      .collection("categories")
      .aggregate([
        {
          $project: {
            categories: 0,
            subcategories: {
              $filter: {
                input: "$subcategories",
                as: "subcategory",
                cond: {
                  if: {
                    $eq: ["$$subcategory._id", "60e51a116678530e84ee2e86"],
                  },
                  then: "$$subcategory",
                  else: "not found",
                },
              },
            },
          },
        },
      ])
      .toArray();
    console.log("answer", r);

    return r;

Expected Output

if i am having the id of any one of the subcategory let 60e95a466f25a34248698a33 then how can i fetch that subcategory if we do not know the category id?

"subcategories":[
  {
    "trans": {
      "en": {
        "name": "Social Media Advertising",
        "description": "Social Media Advertising"
      }
    },
    "$oid": "60e95a466f25a34248698a33",
    "service_type": [
      {
        "trans": {
          "en": {
            "name": "_service1",
            "description": "_service1"
          }
        },
        "_id": {
          "$oid": "60e95a466f25a34248698a30"
        }
      },
      {
        "trans": {
          "en": {
            "name": "Strategy and Planning",
            "description": "Strategy and Planning"
          }
        },
        "_id": {
          "$oid": "60e95a466f25a34248698a31"
        }
      },
      {
        "trans": {
          "en": {
            "name": "AD SETUP AND MANAGEMENT",
            "description": "AD SETUP AND MANAGEMENT"
          }
        },
        "_id": {
          "$oid": "60e95a466f25a34248698a32"
        }
      }
    ]
  }
]
nosql-aggregation aggregation-framework mongodb nosql aggregate
1 Answers

There are 2 problems with that query:

  • You cannot both include and exclude fields in the same projection, except for excluding _id in an include projection.
  • The cond expression inside of a $filter should evaluate to boolean

The $eq operator itself evaluates to boolean, so the additional if is not necessary.

To return only the subcategories field, without _id or any of the category fields, use:

.aggregate([
        {
          $project: {
            _id: 0,
            subcategories: {
              $filter: {
                input: "$subcategories",
                as: "subcategory",
                cond: {
                    $eq: ["$$subcategory._id", "60e51a116678530e84ee2e86"],
                },
              },
            },
          },
        },
      ])
user_22826340
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