MongoDB update a document when exists already with ReactiveMongo - mongodb

Question

I'm writing a Scala web application that use MongoDB as database and ReactiveMongo as driver.
I've a collection named recommendation.correlation in which I saved the correlation between a product and a category.
A document has the following form:
{ "_id" : ObjectId("544f76ea4b7f7e3f6e2db224"), "category" : "c1", "attribute" : "c3:p1", "value" : { "average" : 0, "weight" : 3 } }
Now I'm writing a method as following:
def calculateCorrelation: Future[Boolean] = {
def calculate(category: String, tag: String, similarity: List[Similarity]): Future[(Double, Int)] = {
println("Calculate correlation of " + category + " " + tag)
val value = similarity.foldLeft(0.0, 0)( (r, c) => if(c.tag1Name.split(":")(0) == category && c.tag2Name == tag) (r._1 + c.eq, r._2 + 1) else r
) //fold the tags
val sum = value._1
val count = value._2
val result = if(count > 0) (sum/count, count) else (0.0, 0)
Future{result}
}
play.Logger.debug("Start Correlation")
Similarity.all.toList flatMap { tagsMatch =>
val tuples =
for {
i<- tagsMatch
} yield (i.tag1Name.split(":")(0), i.tag2Name) // create e List[(String, String)] containing the category and productName
val res = tuples map { el =>
calculate(el._1, el._2, tagsMatch) flatMap { value =>
val correlation = Correlation(el._1, el._2, value._1, value._2) // create the correlation
val query = Json.obj("category" -> value._1, "attribute" -> value._2)
Correlations.find(query).one flatMap(element => element match {
case Some(x) => Correlations.update(query, correlation) flatMap {status => status match {
case LastError(ok, _, _, _, _, _, _) => Future{true}
case _ => Future{false}
}
}
case None => Correlations.save(correlation) flatMap {status => status match {
case LastError(ok, _, _, _, _, _, _) => Future{true}
case _ => Future{false}
}
}
}
)
}
}
val result = if(res.exists(_ equals false)) false else true
Future{result}
}
The problem is that the method insert duplicated documents.
Why this happen??
I've solved using db.recommendation.correlation.ensureIndex({"category": 1, "attribute": 1}, {"unique": true, "dropDups":true }), but how can I fixed the problem without using indexes??
What's wrong??

Answer 1

What you want to do is an in-place update. To do that with ReactiveMongo you need to use an update operator to tell it which fields to update, and how. Instead, you've passed correlation (which I assume is some sort of BSONDocument) to the collection's update method. That simply requests replacement of the document, which if the unique index value is different will cause a new document to be added to the collection. Instead of passing correlation you should pass a BSONDocument that uses one of the update operators such as $set (set a field) or $incr (increment a numeric field by one). For details on doing that, please see the MongoDB Documentation, Modify Document