Can not add additional element to (mongoose) object

Question

I have a nodejs express application with an api to return data from a mongodb database. This is my mongoose model:

const bookingSchema = new mongoose.Schema({
  timestamp: {
    type: Date,
    default: Date.now,
    required: true
  },
  tags: {
    type: [String],
    required: true
  },
  amount: {
    type: Number,
    required: true
  },
  type: {
    type: String,
    required: true,
    enum: ['expense', 'income']
  }
})

When I'm calling the api with the path /api/bookings/listbymonth/2019/1 this function inside the backend gets called:

const bookingsListByMonth = (req, res) => {
  const year = ("0000" + req.params.year).slice(-4)
  const month = ("0000" + req.params.month).slice(-2)
  const dateOfMonth = `${year}${month}01`
  const start = moment(dateOfMonth).startOf("month")
  const end = moment(dateOfMonth).endOf("month")

  bookingMongooseModel
    .find({
      timestamp: {
        $gt: start,
        $lt: end
      }
    })
    .sort({ timestamp: 1 })
    .exec((err, bookings) => {
      if (!bookings) {
        return res
          .status(404)
          .json({
            "message": "booking not found"
          })
      } else if (err) {
        return res
          .status(404)
          .json(err)
      }
      res
        .status(200)
        .json(processBookings(bookings));
    })
}

Instead of simply returning the json data, I want to preprocess the data and make a nice timestamp and currency field. That's why the json data runs through an additional processBookings function. For testing I tried to add another field timestamp2: 123:

const processBookings = (bookings) => {
  console.log("Bookings unsorted: \n" + bookings + "\n")

  const mainTags = [
    "Essen",
    "Essen gehen",
    "Notwendiges",
    "Luxus",
  ]

  let bookingsProcessed = []

  mainTags.forEach((tag) => {
    let singleTagBookings = bookings.filter(
      booking => booking.tags.includes(tag)
    )

    singleTagBookings.map((item) => {
      item.timestamp2 = "123"
      return item
    })

    let message = null;
    if (singleTagBookings.length === 0) {
      message = "No bookings found";
    }

    bookingsProcessed.push({
      name: tag,
      bookings: singleTagBookings,
      message: message
    })
  });

  console.log("Bookings sorted:")
  bookingsProcessed.forEach((item) => {
    console.log(item)
  })

  return bookingsProcessed
}

The objects in the bookings array should have another property timestamp2: "123", but they don't. Here's the output:

Bookings unsorted: 
{ tags: [ 'Luxus', 'voluptatem', 'atque', 'qui', 'sunt' ],
  _id: 5cb2c9e1ff6c9c6bef95f56f,
  timestamp: 2019-01-06T08:53:06.945Z,
  amount: 68.02,
  type: 'expense',
  __v: 0 },{ tags: [ 'Essen gehen', 'ut', 'unde', 'et', 'officiis' ],
  _id: 5cb2c9e1ff6c9c6bef95f56e,
  timestamp: 2019-01-09T20:35:06.411Z,
  amount: 33.77,
  type: 'income',
  __v: 0 }

Bookings sorted:     
{ name: 'Essen', bookings: [], message: 'No bookings found' }
{ name: 'Essen gehen',
  bookings: 
   [ { tags: [Array],
       _id: 5cb2c9e1ff6c9c6bef95f56e,
       timestamp: 2019-01-09T20:35:06.411Z,
       amount: 33.77,
       type: 'income',
       __v: 0 } ],
  message: null }
{ name: 'Notwendiges',
  bookings: [],
  message: 'No bookings found' }
{ name: 'Luxus',
  bookings: 
   [ { tags: [Array],
       _id: 5cb2c9e1ff6c9c6bef95f56f,
       timestamp: 2019-01-06T08:53:06.945Z,
       amount: 68.02,
       type: 'expense',
       __v: 0 } ],
  message: null }

As in the comments suggested I tried to use let bookings = [ {tags: ["Essen"]}]; as test data. Here it works. The output is:

Bookings unsorted: 
[object Object]

Bookings sorted:
{ name: 'Essen',
  bookings: [ { tags: [Array], timestamp2: '123' } ],
  message: null }
{ name: 'Essen gehen',
  bookings: [],
  message: 'No bookings found' }
{ name: 'Notwendiges',
  bookings: [],
  message: 'No bookings found' }
{ name: 'Luxus', bookings: [], message: 'No bookings found' }

So I guess it has something to do with my mongoose model restricting to add any additional field. However If I put

console.log("EXTENSIBLE " + Object.isExtensible(bookings))
res
  .status(200)
  .json(processBookings(bookings));

into my bookingsListByMonth function I get:

EXTENSIBLE true

So in theory I should be able to add something to the bookings object?

As a workaround I added the timestamp2 field to my mongoose model:

const bookingSchema = new mongoose.Schema({
  timestamp: {
    type: Date,
    default: Date.now,
    required: true
  },
  timestamp2: {
    type: String,
    default: null
  },
  tags: {
    type: [String],
    required: true
  },
  amount: {
    type: Number,
    required: true
  },
  type: {
    type: String,
    required: true,
    enum: ['expense', 'income']
  }
})

This works, however it adds an additional useless data field into my database. How can I modify the bookings json object returned from the mongodb? If I can't modify it because it is a mongoose model, how can I make a copy that is editable?

Selfevident

nope, the code works as expected ... by the way, your code will change the objects in singleTagBookings too, so, you could just use .forEach instead - are the objects in the Array singleTagBookings sealed perhaps? – Millepore

You must be getting an error singleTagBookings.map is not a function if not than update question with proper code and data – Upheld

The objects are not sealed. Sadly I don't get an error. I have updated my question with the full code. – Selfevident

are they extensible? - your code works just fine, adding timestamp2 ... see your code in action – Millepore

but if you Object.preventExtensions(obj) jsfiddle.net/ybdz3vjp/3 - also sealing and freezing will result in the same output - you can check if an object is able to have properties added by Object.isExtensible(obj) – Millepore

As @JaromandaX reported the code works as posted - try copying it and using let bookings = [ {tags: ["Essen"]}]; for test data. Note that the input version of the bookings array is being updated and must not be frozen or sealed. – Kaiulani

@traktor53 or made non-extensible either – Millepore

Using let bookings = [ {tags: ["Essen"]}]; as test data works. I have elaborated my question. – Selfevident

Answer 1

Documents returned from queries are mongoose documents which restricts addition of new fields. In order to convert mongoose documents into plain JavaScript objects there is a method/option lean in mongoose - https://mongoosejs.com/docs/tutorials/lean.html.

The find query would look something like this

bookingMongooseModel
.find({
  timestamp: {
    $gt: start,
    $lt: end
  }
})
.sort({ timestamp: 1 })
.lean()

Additionally, mongoose provides configurable options for you to set while defining schema. For instance, new Schema({..}, {timestamps: true}); would create two fields in your document createdAt and updatedAt. For more information see Options section here https://mongoosejs.com/docs/guide.html#options

Photosynthesis

Answer 2

Just transform your mongoose object to standard javascript object, with toObject() function. Then you will be able to modify the datas / add new fields / change type of datas :

 const processBookings = (bookings) => {
     bookings = bookings.map(function(e){return e.toObject();});
     ...

Oliy

Answer 3

  singleTagBookings.map((item) => {
      item.timestamp2 = "123"
      return item
    })

I think this is your problem..

1. map returns a new array, so you need to assign it to a variable
2. in the map callback function its better to return a new object than mutate it

so try this instead

singleTagBookings = singleTagBookings.map((item) => ({
       ...item,
       timestamp2: "123"
    }))

Microsurgery