使用Java驱动程序进行MongoDB聚合 [英] MongoDB aggregation with Java driver

问题描述

我需要你帮助将MongoDB聚合框架与java驱动程序一起使用。
我不明白如何编写我的请求，即使使用
感谢此链接

I need your help for using MongoDB aggregation framework with java driver. I don't understand how to write my request, even with this documentation.

I want to get the 200 oldest views from all items in my collection. Here is my mongo query (which works like I want in console mode):

db.myCollection.aggregate(
    {$unwind : "$views"},
    {$match : {"views.isActive" : true}},
    {$sort : {"views.date" : 1}},
    {$limit : 200},
    {$project : {"_id" : 0, "url" : "$views.url", "date" : "$views.date"}}
)

Items in this collection have one or many views. My question is not about the request result, I want to know the java syntaxe.

解决方案

Finally found the solution, I get the same result than with the original request.

Mongo Driver 3 :

Aggregate doc

MongoCollection<Document> collection = database.getCollection("myCollection");

AggregateIterable<Document> output = collection.aggregate(Arrays.asList(
        new Document("$unwind", "$views"),
        new Document("$match", new Document("views.isActive", true)),
        new Document("$sort", new Document("views.date", 1)),
        new Document("$limit", 200),
        new Document("$project", new Document("_id", 0)
                    .append("url", "$views.url")
                    .append("date", "$views.date"))
        ));

// Print for demo
for (Document dbObject : output)
{
    System.out.println(dbObject);
}

You can make it more readable with static import :
import static com.mongodb.client.model.Aggregates.*;.
See koulini answer for complet example.

Mongo Driver 2 :

Aggregate doc

Iterable<DBObject> output = collection.aggregate(Arrays.asList(
        (DBObject) new BasicDBObject("$unwind", "$views"),
        (DBObject) new BasicDBObject("$match", new BasicDBObject("views.isActive", true)),
        (DBObject) new BasicDBObject("$sort", new BasicDBObject("views.date", 1)),
        (DBObject) new BasicDBObject("$limit", 200),
        (DBObject) new BasicDBObject("$project", new BasicDBObject("_id", 0)
                    .append("url", "$views.url")
                    .append("date", "$views.date"))
        )).results();

// Print for demo
for (DBObject dbObject : output)
{
    System.out.println(dbObject);
}

---

Query conversion logic : Thank to this link

这篇关于使用Java驱动程序进行MongoDB聚合的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！