foma foma - 5 months ago 21
Java Question

Retrive a set of documents from array in MongoDB using Java driver

I have a MongoDB document structure like this:

{
"name": "list"
"config": "default"
"items": [
{
"email": "user1@mail.com"
"status": true
"number": 123
},
...
{
"email": "user100@mail.com"
"status": false
"number": 432
},
]
}


Now, how can I retrive multiple subdocuments that much certain criteria. For instance, I want to obtain all documents where status = true. I know that it is possible to use $elemMatch, but it returns only the first matching instance and I need ALL documents that correspond to the specified condition. Please show how can it be done with Java.

Answer

You can do it in Java as follows.

        Mongo mongo = new Mongo("localhost:27017");
        DB db = mongo.getDB("myDB");
        DBCollection coll = db.getCollection("myCollection");

        DBObject statusQuery = new BasicDBObject("status", true);
        DBObject elemMatchQuery = new BasicDBObject("$elemMatch", statusQuery);

        DBObject fields = new BasicDBObject();
        fields.put("items", elemMatchQuery);
        fields.put("name", 1);
        fields.put("config", 1);

        DBCursor cur = coll.find(new BasicDBObject(), fields);

        while (cur.hasNext()) {
            DBObject obj = cur.next();
            // Get fields from object
        }