CODEWITHSUNDEEP
javascriptjsonmap-function
Nikola Stojaković
Nikola Stojaković

Reputation: 2305

Map returns array with undefined values

I want to remove properties _id and __v from Mongo result (which is array with markers) with map, but I always get array with null values in JSON result instead of array with objects without this two properties.

Marker.find().then(result => {
    const markers = result.map(marker => {
        delete marker['_id'];
        delete marker['__v'];
    });
    res.send(JSON.stringify({ markers: markers }));
}).catch(next);

This is how returned JSON looks without mapping:

{
    "markers": [
        {
            "_id": "5a7e266b6d7f6d00147bc269",
            "id": "da27cbf8372aaeb24ce20a21",
            "x": "25",
            "y": "37",
            "timestamp": 2093355239,
            "__v": 0
        },
        {
            "_id": "5a7e2789c61cf90014d67e6b",
            "id": "5580d237f486088499c6d82k",
            "x": "56",
            "y": "29",
            "timestamp": 2138203308,
            "__v": 0
        },
    ]
}

This is how returned JSON looks with mapping:

{
    "markers": [
        null,
        null
    ]
}

Upvotes: 0

Views: 464

Answers (4)

Nikola Stojaković
Nikola Stojaković

Reputation: 2305

Problem is solved. None of given solutions have worked because the problem was about Mongoose. Data returned by Mongoose is MongooseDocument and is not editable. I just had to add lean() method in query to get the editable result. After that, I used Icepickle's solution.

Marker.find().lean().then(result => {
  const markers = result.map(marker => {
    const { ['_id']: _, ['__v']: __, ...rest } = marker;
    return rest;
  });
  res.send(JSON.stringify({ markers: markers }));
}).catch(next);

Upvotes: 0

Slai
Slai

Reputation: 22876

Key value pairs can be filtered in the JSON.stringify replacer parameter :

o = {"markers":[{"_id":"5a7e266b6d7f6d00147bc269","id":"da27cbf8372aaeb24ce20a21","x":"25","y":"37","timestamp":2093355239,"__v":0},{"_id":"5a7e2789c61cf90014d67e6b","id":"5580d237f486088499c6d82k","x":"56","y":"29","timestamp":2138203308,"__v":0}]}

j = JSON.stringify(o, (k, v) => k[0] === '_' ? void 0 : v, 2)

console.log(j)

Upvotes: 0

Icepickle
Icepickle

Reputation: 12796

Instead of deleting (and essentially mutating your result array), you could consider the following 

Marker.find().then(result => {
  const markers = result.map(marker => {
    const { ['_id']: _, ['__v']: __, ...rest } = marker;
    return rest;
  });
  res.send(JSON.stringify({ markers: markers }));
}).catch(next);

which would use destructuring to create a copy of the marker, ommitting the 2 properties that you have previously deleted. So _ would contain the value for _id and __ would contain the value for __V, the remaining part of your object would be contained inside the rest variable

Upvotes: 1

dknaack
dknaack

Reputation: 60466

You need to return something in your map function. The map function returns a new array containing what you return from your map function. If you return nothing it is undefined.

Marker.find().then(result => {
    const markers = result.map(marker => {
        delete marker['_id'];
        delete marker['__v'];
        return marker;
    });
    res.send(JSON.stringify({ markers: markers }));
}).catch(next);

Upvotes: 2

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