mongodb - mapReduce() scope - Undefined values are converted into null values

Question

If I put a variable with an undefined value into the "scope" parameter of mapReduce(), then the map function will receive the variable with a null value (instead of the undefined value). Is that correct?

For example (javascript skeleton for the "mongo" command):

db.mycol.mapReduce(
                        f_map,
                        f_reduce,
                        {
                            scope: { myvar:   undefined}
                        }
                  );

function f_map()
{
    print("myvar: " + myvar);
}

That will print "myvar: null" (instead of "myvar: undefined") into the server log (into the replicaset member log). Are undefined values converted automatically to null values when passing through mapReduce()?

Ross · Accepted Answer · 2013-08-21 11:26:01Z

1

Yes undefined values get translated into null values in mongodb's v8 engine.

The reason for this is to keep backwards compatibility with the older Spider Monkey JS engine and not break existing code that relied on that behaviour.

answered Aug 21, 2013 at 11:26

Ross

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