Databases Reference
In-Depth Information
ignores this scope. It has its own scope key,
"scope"
, and you must use that if there are
client-side values you want to use in your MapReduce. You can set them using a plain
document of the form
variable_name : value
, and they will be available in your
map
,
reduce
, and
finalize
functions. The scope is immutable from within these functions.
For instance, in the example in the previous section, we calculated the recency of a page
using
1/(new Date() - this.date)
. We could, instead, pass in the current date as part
of the scope with the following code:
> db.runCommand({"mapreduce" : "webpages", "map" : map, "reduce" : reduce,
"scope" : {now : new Date()}})
Then, in the
map
function, we could say
1/(now - this.date)
.
Getting more output
There is also a verbose option for debugging. If you would like to see the progress of
your MapReduce as it runs, you can specify
"verbose" : true
.
You can also use
print
to see what's happening in the
map
,
reduce
, and
finalize
func-
tions.
print
will print to the server log.
