Vfrdtyky

Is it possible to add 2 custom fields (that are not exist at my collections), into aggregate group query, using java with mongoDB? My approach is below but it doesn't work

    Double custom_calculated_field1 = 0d;

    Double custom_calculated_field2 = 0d;

    Document customGroup_fields = new Document();

    customGroup_fields.append("customer_id", "$customer_id");

    //custom_calculated fields

    customGroup_fields.append("custom_calculated_field1", custom_calculated_field1);

    customGroup_fields.append("custom_calculated_field2", custom_calculated_field2);

         AggregateIterable<Document> customers_results = customerID.aggregate(

            Arrays.asList(

                    Aggregates.match(values),

                    Aggregates.group(customGroup_fields)

            ));

This is a problem with the way you structure your aggregation. You can read more about it on the Mongo aggregation docs here: https://docs.mongodb.com/manual/aggregation/

Effectively you assume that your pipeline knows what operations you are trying to execute. A pipeline however works very similar to what a unix pipe | does. It executes any command and passes the output to the next. So you need to tell it that your match is a match and the group is a group. I have an example for both Document and DBObject, where DBObject is the more up to date approach I believe. Consider this example:

  @Test

    public void testAggProjection() { 

        DBCollection collection = template.getCollection("test-collection");



        DBObject ob = new BasicDBObject(ImmutableMap.of("test", "value1", "something", "here"));

        DBObject ob2 = new BasicDBObject(ImmutableMap.of("test", "value1", "hello", "world"));

        DBObject ob3 = new BasicDBObject(ImmutableMap.of("test", "value2", "other", "fields"));

        WriteResult insert = collection.insert(ob, ob2, ob3);

        Assert.assertEquals(3, insert.getN());



        DBObject match = new BasicDBObject("$match", new BasicDBObject("test", "value1")); // match the test value 

        Map<String, Object> grouping = new HashMap<>();

        grouping.put("_id", "$test");

        grouping.put("my_count", new BasicDBObject("$sum", 1));

        DBObject group = new BasicDBObject("$group", grouping); // group by 



        AggregationOutput aggregate = collection.aggregate(match, group);

        System.out.println(aggregate.results());

        DBObject next = aggregate.results().iterator().next();

        Assert.assertTrue(next.containsField("_id"));

        Assert.assertTrue(next.containsField("my_count"));





        // with documents raw 

        MongoClient mc = (MongoClient) client;

        MongoCollection<Document> collection2 = mc.getDatabase(template.getDb().getName()).getCollection("test-collection");



        Document dob = new Document(ImmutableMap.of("test", "value1", "something", "here"));

        Document dob2 = new Document(ImmutableMap.of("test", "value1", "hello", "world"));

        Document dob3 = new Document(ImmutableMap.of("test", "value2", "other", "fields"));



        collection2.insertMany(Arrays.asList(dob, dob2, dob3));



        long count = collection2.count();

        Assert.assertEquals(3, count);



        Document match2 = new Document("$match", new Document("test", "value1"));

        Document group2 = new Document("$group", ImmutableMap.of("_id", "$test", "my_count", new Document("$sum", 1)));



        AggregateIterable<Document> aggregate2 = collection2.aggregate(Arrays.asList(match2, group2));

        Document next2 = aggregate2.iterator().next();

        Assert.assertTrue(next2.get("_id") != null);

        Assert.assertTrue(next2.get("my_count") != null);

    }

This is a working unit test. What this does is (in both cases):

• Create a new collection and insert 3 documents.


• Aggregate them with a match, matching 2 documents, and a group where we count the objects we found.

The important bits for you are here:

Document match2 = new Document("$match", new Document("test", "value1"));

        Document group2 = new Document("$group", ImmutableMap.of("_id", "$test", "my_count", new Document("$sum", 1)));



        AggregateIterable<Document> aggregate2 = collection2.aggregate(Arrays.asList(match2, group2));

In my match2 and group2 documents, I define what stage the aggregation is executing as $match and $group.

The resulting Json is then:

Document{{_id=value1, my_count=2}}

I hope that helps!

Please note that the _id field inside the group is mandatory.

Artur