Question

您好我想使用java在mongodb中自动增加_id。我对此完全陌生。在文档中我找到了这样的解决方案：

db.counters.insert(
 {
      _id: "userid",
      seq: 0
   }
)


function getNextSequence(name) {
var ret = db.counters.findAndModify(
{
query: { _id: name },
update: { $inc: { seq: 1 } },
new: true
}
);
return ret.seq;
}

db.users.insert(
{
_id: getNextSequence("userid"),
name: "Sarah C."
}
)

任何人都可以建议我如何使用java做到这一点？我对此完全陌生。

Answer 1

首先使用Create an Auto-Incrementing Sequence Field使用mongoDB shell创建集合，集合应为：

db.counters.insert(
{
  _id: "userid",
  seq: 0
})

所以你得到的counters个集合包含_id,seq之类的字段，现在在java中创建getNextSequence函数，而这个函数的参数userid为字符串，所以getNextSequence功能如下：

public static Object getNextSequence(String name) throws Exception{
    MongoClient mongoClient = new MongoClient( "localhost" , 27017 );
    // Now connect to your databases
    DB db = mongoClient.getDB("demo");
    DBCollection collection = db.getCollection("counters");
    BasicDBObject find = new BasicDBObject();
    find.put("_id", name);
    BasicDBObject update = new BasicDBObject();
    update.put("$inc", new BasicDBObject("seq", 1));
    DBObject obj =  collection.findAndModify(find, update);
    return obj.get("seq");

}

以上函数返回seq计数并在main方法中使用此函数，如：

public static void main(String[] args) throws Exception {

    MongoClient mongoClient = new MongoClient( "localhost" , 27017 );
    // Now connect to your databases
    DB db = mongoClient.getDB("demo");
    DBCollection collection = db.getCollection("counters");
    BasicDBObject document = new BasicDBObject();

    document.put("_id", getNextSequence("userid"));
    document.put("name","Sarah C.");
    collection.insert(document); // insert first doc

    document.put("_id", getNextSequence("userid"));
    document.put("name", "Bob D.");
    collection.insert(document); // insert second doc
}

现在counters集合中包含三个文档，其中包含name分别为Sarah C. and Bob D.和一个我们第一次手动插入的默认文档，它会像seq一样增加{ "_id" : "userid", "seq" : 2 } {1}}

Answer 2

DBCollection collection = database.getCollection("Table Name");

DBObject modifier = new BasicDBObject("counter", 1);
DBObject incQuery = new BasicDBObject("$id", modifier);

使用java在mongodb中自动增加序列

2 个答案: