带有 Java 驱动程序的 MongoDB 聚合

发布于07月29日

我需要你的帮助来使用MongoDB聚合框架和java驱动程序.

我想从我Collection 的所有物品中获取200个最古老的视图.以下是我的mongo查询(它在控制台模式下的工作方式与我所希望的一样):

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

此集合中的项目有一个或多个视图.

推荐答案

最终找到了解决方案，我得到了与原始请求相同的结果.

Mongo驱动程序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驱动程序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