Update multiple fields' value in MongoDB - mongodb

Question

I'm newbie for manipulating MongoDB recently, but I really need to update some fields like these..
db_name: test
table_name: info
{
"_id" : ObjectId("54bf9ab4f8eda6747567b122"),
"archives" : [
{
"evalution" : {
"positive" : 0,
"undefine" : 0,
"negative" : 0
},
"source" : ObjectId("54cb6f455decd8037528756b")
}
]
}
I want to increase positive and undefine by 1, and if evalution doesn't exists,
"evalution" : {
"positive" : 0,
"undefine" : 0,
"negative" : 0
}
should be added to the object.
I don't know if I express myself clearly, but I really need some help..

Answer 1

If evalution doesn't exists u can create a sub-doc using following query.
db.test.update(
{_id:ObjectId("54bf9ab4f8eda6747567b122"),
"archives.source" : ObjectId("54cb6f455decd8037528756b"),
"archives.evalution":{$exists:false}},
{$set:{"archives.$.evalution":{positive:1,negative:0,undefine:1}}}
)
NOTE: Positional operator is only upto one level, so u cannot increment the values until you know the index of archieves array.
you get the the index of the archieves array and increment using following command. In this case 0 where
source = ObjectId("54cb6f455decd8037528756b")
db.test.update(
{_id:_id:ObjectId("54bf9ab4f8eda6747567b122")},
{$inc:{"archives.0.evalution.positive":1}}
)

Answer 2

It would help to know what the semantics of the update are. Why are you incrementing those two fields? Why are you incrementing two fields, as if doing a count, but if the fields don't exist you want to set default values to 0 (as opposed to, say, 1)? Is there a semantic difference between "evaluation doesn't exist" and the value
{
"positive" : 0,
"undefine" : 0,
"negative" : 0
}
for evaluation? Or between "evaluation doesn't exist" and
{
"positive" : -1,
"undefine" : -1,
"negative" : 0
}
for the value? It seems like no, for at least one of those default values, and so you should set evaluation to have the appropriate default value on insert of the document or of the array element. If you do that, your update is simple:
db.info.update(
{
"_id" : ObjectId("54bf9ab4f8eda6747567b122"),
"archives.source" : ObjectId("54cb6f455decd8037528756b")
},
{
"$inc" : {
"archives.$.evalution.positive" : 1,
"archives.$.evalution.undefine" : 1,
}
}
)
Also, you have some typos, I think:
evalution probably means evaluation or possibly evolution?
the proper complement to positive and negative is undefined