Updating specific fields in MongoDB subdocuments (rmongodb) - r

Question

I have some problems understanding the way how specific fields of a subdocument (as opposed to the entire subdocument) can be updated.
I seem to have understood how to query for certain field values in subdocuments, but I'm lost with respect to how a BSON document needs to be structured that only changes the fields queried.
Still feel like I'm not fully understanding how how "plain MongoDB syntax" translates into R syntax and how the update operators exactly work. Any hints in that respect would be greatly appreciated.
Preliminaries
pkg <- "rmongodb"
lib <- file.path(R.home(), "library")
if (!suppressWarnings(require(pkg, lib.loc=lib, character.only=TRUE))) {
install.packages(pkg, lib=lib)
require(pkg, lib.loc=lib, character.only=TRUE)
}
db <- "__test"
ns.0 <- "user"
ns <- paste(db, ns.0, sep=".")
con <- mongo.create(db=db)
Ensuring empty DB
mongo.remove(mongo=con, ns=ns)
Inserting documents
This section simply ensures some example data in the DB. It's just an auxiliary part which you can skip mentally!! Continue with section “Querying“ and see "Actual querying" to get an idea of the document structure which might be hard to grasp from the R code below.
BSON for document 1
blist <- NULL
buf <- mongo.bson.buffer.create()
mongo.bson.buffer.append(buf, name="host",
value="unittest.com")
mongo.bson.buffer.start.array(buf, "paths")
mongo.bson.buffer.start.object(buf, "1")
mongo.bson.buffer.append(buf, name="path",
value="home")
mongo.bson.buffer.append(buf, name="url",
value="www.unittest.com/home")
mongo.bson.buffer.start.array(buf, "queries")
mongo.bson.buffer.start.object(buf, "1")
mongo.bson.buffer.append(buf, name="query",
value="?somequery")
mongo.bson.buffer.append(buf, name="url",
value="www.unittest.com/home?somequery")
mongo.bson.buffer.finish.object(buf) # finish query:1
mongo.bson.buffer.start.object(buf, "2")
mongo.bson.buffer.append(buf, name="query",
value="?someotherquery")
mongo.bson.buffer.append(buf, name="url",
value="www.unittest.com/home?someotherquery")
mongo.bson.buffer.finish.object(buf) # finish query:2
mongo.bson.buffer.finish.object(buf) # finish queries
mongo.bson.buffer.finish.object(buf) # finish path:1
mongo.bson.buffer.start.object(buf, "2")
mongo.bson.buffer.append(buf, name="path",
value="somepage")
mongo.bson.buffer.append(buf, name="url",
value="www.unittest.com/somepage")
mongo.bson.buffer.start.array(buf, "queries")
mongo.bson.buffer.start.object(buf, "1")
mongo.bson.buffer.append(buf, name="query",
value="?somequery")
mongo.bson.buffer.append(buf, name="url",
value="www.unittest.com/somepage?somequery")
mongo.bson.buffer.finish.object(buf) # finish query:1
mongo.bson.buffer.start.object(buf, "2")
mongo.bson.buffer.append(buf, name="query",
value="?someotherquery")
mongo.bson.buffer.append(buf, name="url",
value="www.unittest.com/somepage?someotherquery")
mongo.bson.buffer.finish.object(buf) # finish query:2
mongo.bson.buffer.finish.object(buf) # finish queries
mongo.bson.buffer.finish.object(buf) # finish path:2
mongo.bson.buffer.finish.object(buf) # finish paths
mongo.bson.buffer.finish.object(buf) # finish buf
b <- mongo.bson.from.buffer(buf)
blist <- c(blist, list(b))
BSON for document 2
EDIT 2012-01-23
I removed this section to make the question a bit easier to grasp.
Actual insert
sapply(blist, function(ii) {
mongo.insert(mongo=con, ns=ns, b=ii)
})
Querying
BSON for query
buf <- mongo.bson.buffer.create()
mongo.bson.buffer.start.object(buf, "paths")
mongo.bson.buffer.start.object(buf, "$elemMatch")
mongo.bson.buffer.start.object(buf, "queries")
mongo.bson.buffer.start.object(buf, "$elemMatch")
mongo.bson.buffer.append(buf, name="query", value="?somequery")
mongo.bson.buffer.finish.object(buf)
mongo.bson.buffer.finish.object(buf)
mongo.bson.buffer.finish.object(buf)
mongo.bson.buffer.finish.object(buf)
query <- mongo.bson.from.buffer(buf)
> query
paths : 3
$elemMatch : 3
queries : 3
$elemMatch : 3
query : 2 ?somequery
Actual query
> mongo.find.one(mongo=con, ns=ns, query=query)
_id : 7 50feff31ba54a032514b6181
host : 2 unittest.com
paths : 4
1 : 3
path : 2 home
url : 2 www.unittest.com/home
queries : 4
1 : 3
query : 2 ?somequery
url : 2 www.unittest.com/home?somequery
2 : 3
query : 2 ?someotherquery
url : 2 www.unittest.com/home?someotherquery
2 : 3
path : 2 somepage
url : 2 www.unittest.com/somepage
queries : 4
1 : 3
query : 2 ?somequery
url : 2 www.unittest.com/somepage?somequery
2 : 3
query : 2 ?someotherquery
url : 2 www.unittest.com/somepage?someotherquery
Updating
BSON for update
I would like to set the value of the query field in query subdocuments. I had a look at the MongoDB Manual and tried something like this (using the $set and $ operators because there are arrays involved):
buf <- mongo.bson.buffer.create()
mongo.bson.buffer.start.object(buf, "$set")
mongo.bson.buffer.start.object(buf, "paths")
mongo.bson.buffer.start.object(buf, "$")
mongo.bson.buffer.start.object(buf, "queries")
mongo.bson.buffer.start.object(buf, "$")
mongo.bson.buffer.append(
buf,
name="name",
value="abcd"
)
mongo.bson.buffer.finish.object(buf)
mongo.bson.buffer.finish.object(buf)
mongo.bson.buffer.finish.object(buf)
mongo.bson.buffer.finish.object(buf)
mongo.bson.buffer.finish.object(buf)
bnew <- mongo.bson.from.buffer(buf)
> bnew
$set : 3
paths : 3
$ : 3
queries : 3
$ : 3
name : 2 abcd
Actual update
Apparently, this wasn't a good choice ;-)
res <- mongo.update(mongo=con, ns=ns, criteria=query,
objNew=bnew, flags=mongo.update.multi)
> res
[1] FALSE
2: http://docs.mongodb.org/manual/applications/update/#update-operators zU

Answer 1

Try this for bnew:
buf <- mongo.bson.buffer.create()
mongo.bson.buffer.start.object(buf, "$set")
mongo.bson.buffer.append(buf, "paths.0.queries.1.query", "?newquery")
mongo.bson.buffer.finish.object(buf)
bnew = mongo.bson.from.buffer(buf)
this will replace the 2nd query in the 1st of queries.