findOne use in mapreduce mongodb - mongodb

Question

I want to use findOne in map reduce. What is wrong with my code? My error is:
Command 'mapreduce' failed: exception: map invoke failed: JS Error: TypeError: user has no properties nofile_b:3 (response: { "errmsg" : "exception: map invoke failed: JS Error: TypeError: user has no properties nofile_b:3", "code" : 9014, "ok" : 0.0 })
string map = #"
function() {
var movie = this;
var user = db.users.findOne({UserId : parseInt(movie.UserId)});
emit( movie.UserId, {Name:user.Name});
}";
string reduce = #"
function(key, values) {
var result =values;
return result;
}";
string finalize = #"
function(key, value){
return value;
}";
Under c# code
var collection = database.GetCollection("movies");
var options = new MapReduceOptionsBuilder();
options.SetFinalize(finalize);
options.SetOutput(MapReduceOutput.Inline);
var results = collection.MapReduce(map, reduce, options);
lbResultList.Items.Clear();
foreach (var result in results.GetResults())
{
lbResultList.Items.Add(result.ToJson());
}
I solve my problem map function change
function () {
var user = db.users.find({UserId:this.UserId});
var userName ='';
var userSurName ='';
user.forEach(function(u) {
userName = u.Name;
userSurName = u.SurName;
});
emit(
this._id,
{title: this.Title,category:this.Category,UserName: userName,UserSurName: userSurName}
);
}
I think it is not logical,like sub query this solve. What can I do this case?

Answer 1

It looks like you're trying to do an SQL JOIN. MapReduce is the wrong tool for that. You'll actually want to just break this into an aggregate operation to get an array of UserID's and a query operation to get the names of users:
Something like this in mongo shell:
var UserIDArray = [];
movieCollection.aggregate({$group: {_id: "$UserId"}}).forEach(function (v) {
UserIDArray.push(v._id);
});
UserIDNamePairs = userCollection.find({_id : {$in: UserIdArray}}, {_id: "$name"}).toArray();