Using addToSet inside an array with MongoDB - json

Question

I'm trying to track daily stats for an individual.
I'm having a hard time adding a new day inside "history" and can also use a pointer on updating "walkingSteps" as new data comes in.
My schema looks like:
{
"_id": {
"$oid": "50db246ce4b0fe4923f08e48"
},
"history": [
{
"_id": {
"$oid": "50db2316e4b0fe4923f08e12"
},
"date": {
"$date": "2012-12-24T15:26:15.321Z"
},
"walkingSteps": 10,
"goalStatus": 1
},
{
"_id": {
"$oid": "50db2316e4b0fe4923f08e13"
},
"date": {
"$date": "2012-12-25T15:26:15.321Z"
},
"walkingSteps": 5,
"goalStatus": 0
},
{
"_id": {
"$oid": "50db2316e4b0fe4923f08e14"
},
"date": {
"$date": "2012-12-26T15:26:15.321Z"
},
"walkingSteps": 8,
"goalStatus": 0
}
]
}
db.history.update( ? )
I've been browsing (and attempting) the mongodb documentation but they don't quite break it all the way down to dummies like myself... I couldn't quite translate their examples to my setup.
Thanks for any help.
E = noob trying to learn programming

Answer 1

Adding a day:
user = {_id: ObjectId("50db246ce4b0fe4923f08e48")}
day = {_id: ObjectId(), date: ISODate("2013-01-07"), walkingSteps:0, goalStatus: 0}
db.users.update(user, {$addToSet: {history:day}})
Updating walkingSteps:
user = ObjectId("50db246ce4b0fe4923f08e48")
day = ObjectId("50db2316e4b0fe4923f08e13") // second day in your example
query = {_id: user, 'history._id': day}
db.users.update(query, {$set: {"history.$.walkingSteps": 6}})
This uses the $ positional operator.
It might be easier to have a separate history collection though.
[Edit] On the separate collections:
Adding days grows the document in size and it might need to be relocated on the disk. This can lead to performance issues and fragmentation.
Deleting days won't shrink the document size on disk.
It makes querying easier/straightforward (e.g. searching for a period of time)

Answer 2

Even though #Justin Case puts the right answer he doesn't explain a few things in it extremely well.
You will notice first of all that he gets rid of the resolution on dates and moves their format to merely the date instead of date and time like so:
day = {_id: ObjectId(), date: ISODate("2013-01-07"), walkingSteps:0, goalStatus: 0}
This means that all your dates will have 00:00:00 for their time instead of the exact time you are using atm. This increases the ease of querying per day so you can do something like:
db.col.update(
{"_id": ObjectId("50db246ce4b0fe4923f08e48"),
"history.date": ISODate("2013-01-07")},
{$inc: {"history.$.walkingSteps":0}}
)
and other similar queries.
This also makes $addToSet actually enforce its rules, however since the data in this sub document could change, i.e. walkingSteps will increment $addToSet will not work well here anyway.
This is something I would change from the ticked answer. I would probably use $push or something else instead since $addToSet is heavier and won't really do anything useful here.
The reason for a separate history collection in my view would be what you said earlier with:
Yes, the amount of history items for that day.
So this array contains a set of days, which is fine but it sounds like the figure that you wish to get walkingSteps from, a set of history items, should be in another collection and you set walkingSteps according to the count of the amount of items in that other collection for today:
db.history_items.find({date: ISODate("2013-01-07")}).count();

Answer 3

Referring to MongoDB Manual, $ is the positional operator which identifies an element in an array field to update without explicitly specifying the position of the element in the array. The positional $ operator, when used with the update() method and acts as a placeholder for the first match of the update query selector.
So, if you issue a command to update your collection like this:
db.history.update(
{someCriterion: someValue },
{ $push: { "history":
{"_id": {
"$oid": "50db2316e4b0fe4923f08e12"
},
"date": {
"$date": "2012-12-24T15:26:15.321Z"
},
"walkingSteps": 10,
"goalStatus": 1
}
}
)
Mongodb might try to identify $oid and $date as some positional parameters. $ also is part of the atomic operators like $set and $push. So, it is better to avoid use this special character in Mongodb.