Updating array with push and slice - mongodb

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 } } } )