Question

我的mongodb中有80,000个文件。我正在使用Java驱动程序查询这些文档。我尝试根据特定字段对文档进行排序，然后对此结果应用不同的过滤器。排序选项工作正常，但我无法获得不同的文档。我附上了我的工作实例。

    Document query = new Document("RetweetCount",-1);
    MongoCursor<Document> cursor = collection.find().sort(query).iterator();
    try{
    while(cursor.hasNext()) {
        Document dr = (Document) cursor.next();
        String stat = dr.getString("status");
        int retweetcount = dr.getInteger("RetweetCount");
        //Sort works fine. I have to apply distinct here!!! distinct is based on status field
        System.out.println(retweetcount+"--->"+stat);
    }
    }finally{
        cursor.close();
    }
}

Answer 1

我尝试了这种方法，但却提取了一些不相关的字段。I referred this link

    ArrayList<Document> dd = new ArrayList<Document>();
    //MongoCursor<Document> cursor1 = collection.find().sort(query).iterator();

    Document grouping = new Document("_id","$status");
    grouping.append("text", new Document("$first","$_id"));
    grouping.append("RetweetCount", new Document("$first","$RetweetCount"));
    grouping.append("screen_name", new Document("$first","screen_name") );
    Document group = new Document("$group",grouping);
    System.out.println(group);

    Document sortfields = new Document("RetweetCount",-1);
    Document sort = new Document("$sort",sortfields);

    Document projectfields = new Document("_id",0);
    projectfields.append("_id", "$text");
    projectfields.append("RetweetCount", "$RetweetCount");
    projectfields.append("sn", "$screen_name");
    Document projects = new Document("$project",projectfields);



    AggregateIterable<Document> iterable = collection.aggregate(asList(new Document(group),new Document(sort),new Document(projects)));
    iterable.forEach(new Block<Document>() {
        @Override
        public void apply(final Document document) {
            System.out.println(document.toJson());
        }
    });

输出：

{ "_id" : { "$oid" : "576124fafbfb870794452ac6" }, "RetweetCount" : 643, "sn" : "screen_name" }

它省略了我的文本字段，而是返回id字段。我转发的订单也不正确。此方法工作正常，但结果不同。谁能请你纠正我!!!

在Java 3.2中排序和区分Mongodb

1 个答案: