MongoDB 3.2 Java驱动程序：如何使用AggregateOperation

Question

I am interested in example code for using the MongoDB AggregateOperation driver to perform an $unwind activity. AggregateOperation seems to be associated with the MongoDB version 3+ Java driver.

Using AggregateOperation, how would I unwind the "sizes" array shown below?

{ "_id" : ObjectId("56928aa190f425c1e987abc3d"), "item" : "Fleece-lined jeans", "sizes" : [ "30", "31", "38", "40", "42" ], "count" : 3 }

The aggregation examples I see on this forum seem mostly to use BasicDBObject objects and these apparently do not mix with the version 3 Java API.

Answer 1

You will have to invoke a static method parse inside the import org.bson.Document; class.

So, the below lines of code, should unwind the sizes array object for you in mongodb3.0 driver.

MongoClient client = new MongoClient();
        MongoDatabase mongoDatabase = client.getDatabase("test");
        MongoCollection<Document> mongoCollection = mongoDatabase
                .getCollection("unwind");

        List<Document> pipeline;

        pipeline = Arrays.asList(Document.parse("{$unwind:\"$sizes\"}"));

        List<Document> results = mongoCollection.aggregate(pipeline).into(
                new ArrayList<Document>());

        for (Document cur : results) {
            System.out.println(cur.toJson());
        }

For 3.2 java driver.

import static com.mongodb.client.model.Aggregates.unwind;

Bson unwind = unwind("$sizes");

        List<Bson> pipeline = asList(unwind);

        MongoClient c = new MongoClient();
        MongoCollection<Document> collection = c.getDatabase("test")
                .getCollection("unwind");

        List<Document> results = collection.aggregate(pipeline).into(
                new ArrayList<Document>());

        for (Document cur : results) {
            System.out.println(cur.toJson());
        }
    }

Here test is the database and unwind is the collection. This unwinds the sizes array object and below are the output documents.

{ "_id" : { "$oid" : "5692fed991b81360d23f1b54" }, "item" : "Fleece-lined jeans", "sizes" : "30", "count" : 3.0 }
{ "_id" : { "$oid" : "5692fed991b81360d23f1b54" }, "item" : "Fleece-lined jeans", "sizes" : "31", "count" : 3.0 }
{ "_id" : { "$oid" : "5692fed991b81360d23f1b54" }, "item" : "Fleece-lined jeans", "sizes" : "38", "count" : 3.0 }
{ "_id" : { "$oid" : "5692fed991b81360d23f1b54" }, "item" : "Fleece-lined jeans", "sizes" : "40", "count" : 3.0 }
{ "_id" : { "$oid" : "5692fed991b81360d23f1b54" }, "item" : "Fleece-lined jeans", "sizes" : "42", "count" : 3.0 }

Above code didn't use DBObject class which is deprecated in 3.0 version of MongoDB java driver.

Have tested the 3.0 version of code in 3.2 version of mongodb driver and it produced the same result.

Answer 2

I tried this solution. It is based on This documentation

AggregateIterable<Document> iterable = db.getCollection("inventory").aggregate(asList(
            new Document("$unwind", "$sizes")
            ));

    iterable.forEach(new Block<Document>() {
        public void apply(Document document) {
            System.out.println(document.toJson());
        }
    });