Specify Return Format

Question

Is there a way in mongo for me to specify a format of how I want data returned?

I would like to be able to return items as an array if possible. Lets look at this very basic example:

{
    color: red
},
{
    color: white
},
{
    color: blue
}

So for this example I would like to get the above documents as an array:

{
    colors: [red, white, blue]
}

Is there any way to specify how to return items? I know I can specify which columns to get, but then I have to loop through them to build the array. I am hoping mongodb has this built in, as it can probably do it faster than node, php, java, etc.

Answer 1

Use aggregation framework. The aggregation pipeline would simply have a $group operation where the $addToSet operator adds the values to an array. For instance, with a collection which has sample documents:

/* 1 */
{
    "_id" : ObjectId("553c0101dddf8dcf96bdcdea"),
    "color" : "red"
}

/* 2 */
{
    "_id" : ObjectId("553c0101dddf8dcf96bdcdeb"),
    "color" : "white"
}

/* 3 */
{
    "_id" : ObjectId("553c0101dddf8dcf96bdcdec"),
    "color" : "blue"
}

The following aggregation

db.collection.aggregate([
    {
        "$group": {
            "_id": 0,
            "colors": {
                "$addToSet": "$color"
            }
        }
    },
    {
        "$project": {
            "_id": 0,
            "colors": 1
        }
    }
])

will produce the desired output:

/* 1 */
{
    "result" : [ 
        {
            "colors" : [ 
                "blue", 
                "white", 
                "red"
            ]
        }
    ],
    "ok" : 1
}