Push an object into a nested array in MongoDB

Question

I've got a head-scratcher here that I'd like to share with you all.

So here's the model:

    _id: ObjectId()
    name: String,
    columns: [
      {
        name: String,
        _id: ObjectId()
        tasks: [
          {
            title: String,
            description: String,
            status: String,
            _id: ObjectId()
            subtasks: [
              {
                title: String,
                isCompleted: Boolean,
              },
            ],
          },
        ],
      },
    ],
  });

and the query:

exports.createSubtask = (req, res) => {
  if (!req.body) {
    res.status(400).send({ message: "Task name can not be empty!" });
    return;
  }

  const board = req.params.board;
  const column = req.params.column;
  const task = req.params.task;

  Board.findOneAndUpdate(
    {
      _id: board,
      "columns._id": column,
      "columns.tasks._id": task,
    },
    {
      $push: {
        "columns.$.tasks.$.subtasks": req.body,
      },
    }
  )
    .then((data) => {
      if (!data) {
        res.status(404).send({
          message: `Cannot update Task with id=${task}. Maybe task was not found!`,
        });
      } else res.send({ message: "Task was updated successfully." });
    })
    .catch((err) => {
      res.status(500).send({
        message: "Error updating Task with id=" + task,
      });
    });
};

I'm trying to push an object into the subtasks array with $push, but Postman is throwing an error.

Any ideas as to what I'm doing wrong? Appreciate the help.

Golden Ratio

However, I was able to successfully push an object into the tasks array with the following query:

exports.createTask = (req, res) => {
  if (!req.body) {
    res.status(400).send({ message: "Task name can not be empty!" });
    return;
  }

  const board = req.params.board;
  const column = req.params.column;

  Board.findOneAndUpdate(
    {
      _id: board,
      "columns._id": column,
    },
    {
      $push: {
        "columns.$.tasks": req.body,
      },
    }
  )
    .then((data) => {
      if (!data) {
        res.status(404).send({
          message: `Cannot update Column with id=${column}. Maybe column was not found!`,
        });
      } else res.send({ message: "Column was updated successfully." });
    })
    .catch((err) => {
      res.status(500).send({
        message: "Error updating Column with id=" + column,
      });
    });
};

Yong Shun · Accepted Answer · 2023-01-11 23:36:19Z

2

It is not possible to use multiple positional $ for the nested array as mention in docs:

The positional $ operator cannot be used for queries which traverse more than one array, such as queries that traverse arrays nested within other arrays, because the replacement for the $ placeholder is a single value

You should work with the positional filtered operator $[<identifier>].

Board.findOneAndUpdate(
    {
      _id: board,
      "columns._id": column,
      "columns.tasks._id": task,
    },
    {
      $push: {
        "columns.$.tasks.$[task].subtasks": req.body,
      },
    },
    {
      arrayFilters: [
        { "task._id": task }
      ]
    }
  )
.then(...);

Note: Ensure that the passed in task is ObjectId type.

answered Jan 11, 2023 at 23:36

Yong Shun

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Comments

John · Accepted Answer · 2023-01-13 02:35:46Z

0

Credit to Yong Shun Yong for the help. Through trial and error, I solved the problem with the following code

 Board.findOneAndUpdate(
{
  _id: board,
  "columns._id": column,
},
{
  $push: {
    "columns.$.tasks.$[].subtasks": req.body,
  },
},
{
  arrayFilters: [{ "task._id": task }],
}

)

answered Jan 13, 2023 at 2:35

John

531 silver badge7 bronze badges

2 Comments

Yong Shun Over a year ago

Hi, if you $[] all positional operator, you can remove the arrayFilters part. As arrayFilters part we use to filter the document within nested array, but for your current query, that part is not needed.

John Over a year ago

You're absolutely right. I reverted to your solution and it worked. It turns out, I put an 's' after task in the $[] subarray.

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