Get value from Embedded Document Mongo Java

Question

I have the following document in mongo:

>  {    "_id": ObjectId("569afce4b932c542500143ec"),    
>    "date": "2016-1-17T2:31:0Z",    
>    "day": NumberInt(17),    
>    "model1": {
>      "date": "2016-01-17T02:31+0000",
>      "MondayModel": {
>        "gtxdotdot": {
>          "xdotdot": 0,
>          "xdot": 0
>       },
>        "lsxdotdot": {
>          "xdotdot": 0,
>          "xdot": 0
>       },
>        "gtxdot": {
>          "xdotdot": 0,
>          "xdot": 0
>       },
>        "lsxdot": {
>          "xdotdot": 0,
>          "xdot": 0
>       },
>        "modeldotdot": {
>          "mean": 0,
>          "sdvar": 0
>       },
>        "modeldot": {
>          "mean": 0,
>          "sdvar": 0
>       }
>     } 
>     }

I wish to both find this document and extract only the values of model1.MondayModel.gtxdotdot.xdotdot/xdot/mean/sdvar ...

My current code does so with the following:

MongoCursor<Document>  back = collection.find(and(eq("topic",topic),eq("sp",sp))).limit(1).iterator();
if (back.hasNext())
{
    Document doc = back.next();
    Document tmpddc1 = (Document)doc.get("model1");
    Document tmpddc2 = (Document)tmpddc1.get("MondayModel");

    Document tmpddc3 = (Document)tmpddc2.get("gtxdotdot");
    gtxdotdotXdotdot = tmpddc3.getDouble("xdotdot");
    gtxdotdotXdot    = tmpddc3.getDouble("xdot");

             tmpddc3 = (Document)tmpddc2.get("lsxdotdot");
    lsxdotdotXdotdot = tmpddc3.getDouble("xdotdot");
    lsxdotdotXdot    = tmpddc3.getDouble("xdot");

             tmpddc3 = (Document)tmpddc2.get("gtxdot");
    gtxdotXdotdot = tmpddc3.getDouble("xdotdot");
    gtxdotXdot    = tmpddc3.getDouble("xdot");            

             tmpddc3 = (Document)tmpddc2.get("lsxdot");
    lsxdotXdotdot = tmpddc3.getDouble("xdotdot");
    lsxdotXdot    = tmpddc3.getDouble("xdot");  


             tmpddc3 = (Document)tmpddc2.get("modeldotdot");
    modeldotdotXmean = tmpddc3.getDouble("mean");
    modeldotdotXsdvar    = tmpddc3.getDouble("sdvar");             

             tmpddc3 = (Document)tmpddc2.get("modeldot");
    modeldotXmean = tmpddc3.getDouble("mean");
    modeldotXsdvar    = tmpddc3.getDouble("sdvar");                         

}

Instead of running thought he document (as above) is there a way to get the values using the dot notation [model1.MondayModel.gtxdotdot.xdotdot] ? Something such as:

double value =  doc.getDouble("model1.MondayModel.gtxdotdot.xdotdot");

Answer 1

You can do it one of three ways.

You can use aggregation framework to project the value of embedded field using dot notation.

Using Aggregation

 import static com.mongodb.client.model.Aggregates.*;
 import static com.mongodb.client.model.Filters.eq;
 import static com.mongodb.client.model.Projections.computed;
 import static java.util.Arrays.*;
 import static com.mongodb.client.model.Projections.include;

 MongoClient mc = new MongoClient();
 MongoDatabase db = mc.getDatabase("test");
 MongoCollection<Document> collection = db.getCollection("collection");
 Document document = 
     collection.aggregate(asList(
        match(eq("day",17)),
        project(computed("val", "$model1.MondayModel.gtxdotdot.xdotdot")))).
     first();
 Double embeddedField = document.getDouble("val");

Using Distinct

 Double embeddedField = collection.distinct("model1.MondayModel.gtxdotdot.xdotdot", eq("day",17), Double.class).first();

Using Find

 Document document = collection.find(eq("day",17)).projection(include("model1.MondayModel.gtxdotdot.xdotdot")).first();
 Double embeddedField = document.get("model1", Document.class).get("MondayModel", Document.class).get("gtxdotdot", Document.class).getDouble("xdotdot")

Answer 2

I don't think you can use dot notation directly, but you can create your own helper function.

Solution 1: get field with dot notation

public static Object getWithDotNotation( Document document, String dots ) 
     throws MongoException{

    String[] keys = dots.split( "\\." );
    Document doc = document;

    for( int i = 0; i < keys.length - 1; i++ ){
        Object o = doc.get( keys[ i ] );
        if( o == null || !( o instanceof Document ) ){
            throw new MongoException( String.format( 
                    "Field '%s' does not exist or s not a Document", keys[ i ] ) );
        }
        doc = ( Document ) o;
    }//end for

    return doc.get( keys[ keys.length - 1 ] );
}

You can then use it like this:

String dotNotation = "model1.MondayModel.gtxdotdot.xdotdot";

FindIterable<Document> projection = mongoColl.find()
    .projection( fields( include( dotNotation ) ) );

Double value = ( Double ) getWithDotNotation( projection.first(), dotNotation );

System.out.println( value ); // result: 0.0

This will simplify your code a whole lot. The only things to care for are:

• if you are not sure of you dot notation, use a try catch block
• the method getWithDotNotation might return null
• be careful about forced casts, use it only if you are 100% sure of the type of your data (here Double).

Solution 2: flatten your doc

public static Document flattenDoc( Document document ){

    Document flattened = new Document();
    Queue<Pair<String, Document>> queue = new ArrayDeque<>();
    queue.add( new Pair<>( "", document ) );

    while( !queue.isEmpty() ){
        Pair<String, Document> pair = queue.poll();
        String key = pair.getKey();
        for( Map.Entry<String, Object> entry : pair.getValue().entrySet() ){
            if( entry.getValue() instanceof Document ){
                queue.add( new Pair<>( key + entry.getKey() + ".", ( Document ) entry.getValue() ) );

            }else{
                flattened.put( key + entry.getKey(), entry.getValue() );

            }
        }//end for
    }

    return flattened;
}

With your sample data, the result of flattenDoc is the following:

Document{{_id=569afce4b932c542500143ec,
date=2016-1-17T2:31:0Z,
day=17,
model1.date=2016-01-17T02:31+0000,
model1.MondayModel.gtxdotdot.xdotdot=0.0,
model1.MondayModel.gtxdotdot.xdot=0.0,
model1.MondayModel.lsxdotdot.xdotdot=0.0,
model1.MondayModel.lsxdotdot.xdot=0.0,
model1.MondayModel.gtxdot.xdotdot=0.0,
model1.MondayModel.gtxdot.xdot=0.0,
model1.MondayModel.lsxdot.xdotdot=0.0,
model1.MondayModel.lsxdot.xdot=0.0,
model1.MondayModel.modeldotdot.mean=0.0,
model1.MondayModel.modeldotdot.sdvar=0.0,
model1.MondayModel.modeldot.mean=0.0,
model1.MondayModel.modeldot.sdvar=0.0}}

So you can use getDouble("model1.MondayModel.gtxdotdot.xdotdot") directly. This approach might be more efficient if you need to access all the fields.