Mongodb, search object in nested Array

Question

I have these type of items on mongodb:

    {
    "_id": { "$oid" : "2" },
    "waypoints": [
        {
          "step": 0,
          "coordinates": [1,2]
        },
        {
          "step": 1,
          "coordinates": [1,3]
        },
        {
          "step": 2,
          "coordinates": [1,4]
        }
    ]
}

I tried to find [1,2] in the collection to retrieve waypoints.step and the _id, but the result is not what i expected.

I want to get:

{
    "_id": { "$oid" : "2" },
    "waypoints": [
        {
                "step": 0
        }
    ]
}

but i get:

{
    "_id": { "$oid" : "2" },
    "waypoints": [
        {
          "step": 0,
        },
        {
          "step": 1,
        },
        {
          "step": 2,
        }
    ]
}

what is the correct query to achieve what i want?

I know only the coordinates, i need to retrive _id of the object and the step corresponding to the coordinates I'm looking for.

thanks

Parvin Gasimzade · Accepted Answer · 2014-01-10 15:17:14Z

1

You can do it by projecting data. The query should be :

db.collection.find({"_id": { "$oid" : "2" }},{waypoints : {$elemMatch : {coordinates:[1,2]}}})

For more information check $elemMatch operator.

edited Jan 10, 2014 at 15:17

answered Jan 10, 2014 at 14:57

Parvin Gasimzade

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2 Comments

user3182225 Over a year ago

I know only the coordinates, i need to retrive _id and the step corresponding to the coordinates I'm looking for

Parvin Gasimzade Over a year ago

I have updated my answer. This query will return the _id and step that belongs to the given coordinates.

JohnnyHK · Accepted Answer · 2014-01-10 15:29:29Z

0

Because you're searching by coordinates, you can do it like this:

db.test.find({'waypoints.coordinates': [1,2]}, {'waypoints.$': 1})

In the projection, $ represents the index of the waypoints array where the coordinate was found.

You'll get the coordinates value along with the step, but that's the best you can do:

{
  "_id": "2",
  "waypoints": [
    {
      "step": 0,
      "coordinates": [
        1,
        2
      ]
    }
  ]
}

answered Jan 10, 2014 at 15:29

JohnnyHK

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