Something is wrong with '$' index for updating mongodb data - mongodb

Question

Given a mongodb data of
{
"_id" : ObjectId("552f283dd951e49c6f2f451d"),
"uuid" : "1-2-1-b95a4040-e29d-11e4-bce8-0381ce4bc8a5",
"sub" : [
{
"prod" : 30,
"var" : 0,
"status" : "Test",
"files" : [
{
"filePath" : "20150415/2-1/21001429153881552f2859699769.82145796.jpg"
},
{
"filePath" : "20150415/2-1/21001429153880552f28589ca9a8.67013013.jpg"
}
]
},
{
"prod" : 10,
"var" : 0,
"status" : "Pending",
"files" : []
}
],
"process_marker" : 3
}
I would want to update the status of "sub.status" where "uuid" : "1-2-1-b95a4040-e29d-11e4-bce8-0381ce4bc8a5", "sub.prod":10, "sub.prod":0
Normally we'd use the "$" to modify the resulting index as seen below:
use targetDB
db.collection.update({
"uuid" : "1-2-1-b95a4040-e29d-11e4-bce8-0381ce4bc8a5",
"sub.prod":10,
"sub.var":0
},{
"$set":{"sub.$.status":"MyNewValue"}
})
==== BUT THE CODE ABOVE DOES NOT UPDATE THE CORRECT $ TARGET ====
It updates the "prod":30, "var":0 set... Why is that?
If we limit the query conditions for two key value pairs as seen below, the correct array set is updated
use targetDB
db.collection.update({
"uuid" : "1-2-1-b95a4040-e29d-11e4-bce8-0381ce4bc8a5",
"sub.prod":10
},{
"$set":{"sub.$.status":"MyNewValue"}
})
==== THE CODE ABOVE UPDATES THE CORRECT $ TARGET ====
I'm confused that a more detailed find query would result in updating the wrong array set. Is this a bug or did I do something wrong?
MongoDB version : 3.0.2

Answer 1

There is no bug in mongoDB, problem in your query is that you used first match "sub.prod":10 and then "sub.var":0 but in updated it takes latest value in your case "sub.var":0 takes and match first matching array where "sub.var":0 that why it updated only "prod" : 30 array element. More ref. click here.
In this case you should use mongo $elemMatch with $and conditions as below
db.collectionName.update({
"uuid": "1-2-1-b95a4040-e29d-11e4-bce8-0381ce4bc8a5",
"sub": {
"$elemMatch": {
"$and": [{
"prod": 10
}, {
"var": 0
}]
}
}
}, {
"$set": {
"sub.$.status": "MyNewValue"
}
})