How can I find a document in an array with MongoDB API Java?

Question

Here's my code

ServerAddress sa = new ServerAddress("localhost", 27017);
MongoClient mongoClient = new MongoClient(sa);
MongoDatabase db = mongoClient.getDatabase("waitinglist");
MongoCollection<Document> coll = db.getCollection("users");
MongoCursor<Document> f = coll.find(eq("users.email", "[email protected]")).iterator();
try {
while (f.hasNext()) {
    System.out.println("Mongo Cursor: " +f.next().toJson());
}
} finally {
  f.close();
}

And here is how my collection looks:

{ 
"_id" : ObjectId("560b8b76a37991ab2d650ca9"), 
"users" : [
    {
        "firstname" : "Marc", 
        "lastname" : "Berger", 
        "email" : "[email protected]", 
        "phone" : "12345"
    }, 
    {
        "firstname" : "Arnold", 
        "lastname" : "Schwarzenegger", 
        "email" : "[email protected]", 
        "phone" : "12345"
    }]
}

I bassically want to get the document in users where the email is equal [email protected], but it returns the whole document with the array as one. I think the problem is the first parameter in the eq method but I can't find a solution on google how make that statement.

Possible duplicate of Retrieve only the queried element in an object array in MongoDB collection It's a commonly asked question and there are many possible solutions explained there. The basic ones in your case mean the use of the positional $ operator in projection. — Blakes Seven
– Blakes Seven, Commented Oct 1, 2015 at 11:59
I think they are working with the BasicDBObject which are used if you use the '.getDB()' method but this method deprecated so I have to use '.getDatabase()' which returns a MongoDatabase. — marcmaann
– marcmaann, Commented Oct 1, 2015 at 12:16
The positional $ operator has nothing to do with anything deprecated as it's a basic construct. In projection this tells MongoDB to only return the first matched element of the array. Other solutions there have multiple uses of aggregate to return "multiple" matches. Look for using "projection" of fields in your query. The solutions scale over all languages and drivers as it's just the basic way this is done with MongoDB. — Blakes Seven
– Blakes Seven, Commented Oct 1, 2015 at 12:19
Ok, I understand but i still don't know how to put the find command together. — marcmaann
– marcmaann, Commented Oct 1, 2015 at 12:39

Blakes Seven · Accepted Answer · 2015-10-01 13:12:06Z

2

You use the positional $ operator in projection in order to return only the matched element of the array. This uses the .projection() method upon .find() with the MongoDB 3.x java driver:

MongoCursor<Document> f = coll.find(eq("users.email", "[email protected]"))
    .projection(new Document("users.$",1)).iterator();

Then all results will only return the matched array element rather than all array elements.

answered Oct 1, 2015 at 13:12

Blakes Seven

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