How to execute MongoDB native query (JSON) using mongo-java-driver only?

Question

How to fire mongo native queries using java-mongo-driver only.

No Spring-Data or EclipseLink or Hibernate OGM, Only using java-mongo-driver

Sample query :

db.orders.aggregate([
   {
      $unwind: "$specs"
   },
   {
      $lookup:
         {
            from: "inventory",
            localField: "specs",
            foreignField: "size",
            as: "inventory_docs"
        }
   },
   {
      $match: { "inventory_docs": { $ne: [] } }
   }
])

Bolognese

From offical documentation: mongodb.github.io/mongo-java-driver/3.5/driver/tutorials/… – Butterfingers

Are you asking how to express that above aggregate operation using the Java driver? Or are you asking if you can pass the above string into the Java driver and have the driver execute it? – Rand

Answer 1

If your question is:

Can I pass the above string into the Java driver and have the driver execute it?

Then you could use the db.eval command. For example:

MongoDatabase database = mongoClient.getDatabase("...");

Bson command = new Document("eval", "db.orders.aggregate([\n" +
        "   {\n" +
        "      $unwind: \"$specs\"\n" +
        "   },\n" +
        "   {\n" +
        "      $lookup:\n" +
        "         {\n" +
        "            from: \"inventory\",\n" +
        "            localField: \"specs\",\n" +
        "            foreignField: \"size\",\n" +
        "            as: \"inventory_docs\"\n" +
        "        }\n" +
        "   },\n" +
        "   {\n" +
        "      $match: { \"inventory_docs\": { $ne: [] } }\n" +
        "   }\n" +
        "])");
Document result = database.runCommand(command);

But ... the db.eval command is deprecated and its usage is not advised. The MongoDB Java driver can be used to execute your aggregation but not in its 'string form', instead you would use the Java driver's aggregation helpers to create a Java form of your aggregation command. Plenty of details on this in the docs.

Here's an (untested) example using a 3.x MongoDB Java Driver ...

MongoCollection<Document> collection = mongoClient.getDatabase("...").getCollection("...");

AggregateIterable<Document> documents = collection.aggregate(Arrays.asList(
        // the unwind stage
        new Document("$unwind", "$specs"),

        // the lookup stage
        new Document("$lookup", new Document("from", "inventory")
                .append("localField", "specs")
                .append("foreignField", "size")
                .append("as", "inventory_docs")),

        // the match stage
        new Document("$match", new Document("inventory_docs", new BasicDBObject("$ne", new String[0])))
));

.. this might help you to see the form of translation from shell script to Java.

Rand

Answer 2

I was running out of time so used following workaround. Will explore Morcos suggestion in detail later. But following code also works.

import com.infrasoft.mongo.MongoClientFactory;
import com.mongodb.BasicDBList;
import com.mongodb.BasicDBObject;
import com.mongodb.CommandResult;
import com.mongodb.DB;
import com.mongodb.DBObject;
import com.mongodb.util.JSON;

/**
 *
 * @author charudatta.joshi
 */
public class TestNaiveQuery1 {

    public static void main(String[] args) {

        String nativeQuery = "db.orders.aggregate([\n"
                + "   {\n"
                + "      $unwind: \"$specs\"\n"
                + "   },\n"
                + "   {\n"
                + "      $lookup:\n"
                + "         {\n"
                + "            from: \"inventory\",\n"
                + "            localField: \"specs\",\n"
                + "            foreignField: \"size\",\n"
                + "            as: \"inventory_docs\"\n"
                + "        }\n"
                + "   },\n"
                + "   {\n"
                + "      $match: { \"inventory_docs\": { $ne: [] } }\n"
                + "   }\n"
                + "])";

        DBObject command = new BasicDBObject();
        DB db = MongoClientFactory.getMongoClientFactory().getMongoClient().getDB("frms_data_demo");

        nativeQuery = "function() { return (" + nativeQuery + ").toArray(); }";

        //command.put("eval", "function() { return db." + collectionName + ".find(); }");
        command.put("eval", nativeQuery);
        CommandResult result = db.command(command);

        BasicDBList dbObjList = (BasicDBList) result.toMap().get("retval");

        DBObject dbo0 = (BasicDBObject) dbObjList.get(0);
        DBObject dbo1 = (BasicDBObject) dbObjList.get(0);

        System.out.println(dbObjList.get(0));
        System.out.println(dbObjList.get(1));
        // .... just loop on dbObjList

    }


}

Bolognese

Answer 3

this query Deprecated since version 3.0. https://docs.mongodb.com/manual/reference/method/db.eval/ ,i used mongodb4.0 cluster ,not support eval function,

Fatsoluble

Is there any other way to solve it，Thanks！@Charudatta Joshi – Fatsoluble

come up with code samples. Before posting the questions here please learn how to ask the question to get the assured answer. Refer this: stackoverflow.com/help/how-to-ask – Kernan

Answer 4

@aaronwang4love You can try below code. Not tested. Don't have access to environment now. Please update if it works.

BasicDBObject query = BasicDBObject.parse("{userId: {$gt: \"1\"}}"); 
FindIterable<Document> dumps = crapCollection.find(query);

OR You can Also use com.mongodb.util.JSON

DBObject dbObject = (DBObject)JSON.parse("{userId: {$gt: \"1\"}}");

Bolognese