Updating array with push and slice

Question

I have just started to play with MongoDB and have some questions about how I update my documents in the database. I insert two documents in my db with

db.userscores.insert({name: 'John Doe', email: 'john.doe@mail.com', levels : [{level: 1, hiscores: [90, 40, 25], achivements: ['capture the flag', 'it can only be one', 'apple collector', 'level complete']}, {level: 2, hiscores: [30, 25], achivements: ['level complete']}, {level: 3, hiscores: [], achivements: []}]});
db.userscores.insert({name: 'Jane Doe', email: 'jane.doe@mail.com', levels : [{level: 1, hiscores: [150, 90], achivements: ['Master of the universe', 'capture the flag', 'it can only be one', 'apple collector', 'level complete']}]});

I check if my inserting worked with the find() command and it looks ok.

db.userscores.find().pretty();
{
        "_id" : ObjectId("5358b47ab826096525d0ec98"),
        "name" : "John Doe",
        "email" : "john.doe@mail.com",
        "levels" : [
                {
                        "level" : 1,
                        "hiscores" : [
                                90,
                                40,
                                25
                        ],
                        "achivements" : [
                                "capture the flag",
                                "it can only be one",
                                "apple collector",
                                "level complete"
                        ]
                },
                {
                        "level" : 2,
                        "hiscores" : [
                                30,
                                25
                        ],
                        "achivements" : [
                                "level complete"
                        ]
                },
                {
                        "level" : 3,
                        "hiscores" : [ ],
                        "achivements" : [ ]
                }
        ]
}
{
        "_id" : ObjectId("5358b47ab826096525d0ec99"),
        "name" : "Jane Doe",
        "email" : "jane.doe@mail.com",
        "levels" : [
                {
                        "level" : 1,
                        "hiscores" : [
                                150,
                                90
                        ],
                        "achivements" : [
                                "Master of the universe",
                                "capture the flag",
                                "it can only be one",
                                "apple collector",
                                "level complete"
                        ]
                }
        ]
}

How can I add/update data to my userscores? Lets say I want to add a hiscore to user John Doe on level 1. How do I insert the hiscore 75 and still have the hiscore array sorted? Can I limit the number of hiscores so the array only contains 3 elements? I have tried with

db.userscores.aggregate(
    // Initial document match (uses name, if a suitable one is available)
    { $match: {
        name : 'John Doe'
    }},

    // Expand the levels array into a stream of documents
    { $unwind: '$levels' },

    // Filter to 'level 1' scores 
    { $match: {
        'levels.level': 1
    }},

    // Add score 75 with cap/limit of 3 elements
    { $push: {
        'levels.hiscore':{$each [75], $slice:-3}
    }}
);

but it wont work, the error I get is "SyntaxError: Unexpected token [".

And also, how do I get the 10 highest score from all users on level 1 for example? Is my document scheme ok or can I use a better scheme for storing users hiscores and achivements on diffrent levels for my game? Is there any downsides on quering or performance using they scheme above?

Answer 1

You can add the score with this statement:

db.userscores.update(
  { "name": "John Doe", "levels.level": 1 }, 
  { "$push": { "levels.$.hiscores": 75 } } )

This will not sort the array as this is only supported if your array elements are documents.

In MongoDB 2.6 you can use sorting also for non-document arrays:

db.userscores.update(
  { "name": "John Doe", "levels.level": 1 }, 
  { "$push": { "levels.$.hiscores": { $each: [ 75 ], $sort: -1, $slice: 3 } } } )