MongoDB aggregate - Set boolean value in each element in an array based on existence of objects in another array

Question

I have a aggregation pipeline that currently returns example list:

[
    {
        "_id": "5b527a2bfadb811c4869e802",
        "tasks": [
            {
                "done": false,
                "_id": "5b53494987eea4171d199dd3"
            },
            {
                "done": false,
                "_id": "5b53495087eea4171d199dd4"
            },
            {
                "done": false,
                "_id": "5b53495987eea4171d199dd5"
            }
        ],
        "doneTasks_ids": [
            "5b53494987eea4171d199dd3",
            "5b53495087eea4171d199dd4"
        ]
    },
    {
        "_id": "5b527a2ffadb811c4869e803",
        "tasks": [
            {
                "done": false,
                "_id": "5b53496b87eea4171d199dd6"
            },
            {
                "done": false,
                "_id": "5b53497287eea4171d199dd7"
            }
        ],
        "doneTasks_ids": [
            "5b53497287eea4171d199dd7"
        ]
    }
]

Now I want to set done flag for each tasks.done element to true only when the tasks._id is present in doneTasks_ids. I'm pretty sure I should use $map and $in operators, however I'm currently not able to achieve the effect I need. Any help is greatly appreciated

Ashh · Accepted Answer · 2018-07-21 17:53:06Z

You can try below aggregation

Basically you need to loop over each task through $map aggregation and check for the _id in doneTasks_ids array with $in aggregation

db.collection.aggregate([
  { "$addFields": {
    "tasks": {
      "$map": {
        "input": "$tasks",
        "as": "task",
        "in": {
          "_id": "$$task._id",
          "done": {
            "$in": ["$$task._id", "$doneTasks_ids"]
          }
        }
      }
    }
  }}
])

Output

[
  {
    "_id": "5b527a2bfadb811c4869e802",
    "doneTasks_ids": [
      "5b53494987eea4171d199dd3",
      "5b53495087eea4171d199dd4"
    ],
    "tasks": [
      {
        "_id": "5b53494987eea4171d199dd3",
        "done": true
      },
      {
        "_id": "5b53495087eea4171d199dd4",
        "done": true
      },
      {
        "_id": "5b53495987eea4171d199dd5",
        "done": false
      }
    ]
  },
  {
    "_id": "5b527a2ffadb811c4869e803",
    "doneTasks_ids": [
      "5b53497287eea4171d199dd7"
    ],
    "tasks": [
      {
        "_id": "5b53496b87eea4171d199dd6",
        "done": false
      },
      {
        "_id": "5b53497287eea4171d199dd7",
        "done": true
      }
    ]
  }
]

You can try it here

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