使用java在mongodb中自动增加序列

Question

嗨,我想_id使用java在mongodb中自动增加.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

首先使用创建自动递增序列字段,您应该使用mongoDB shell创建集合,集合应为:

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

所以你得到counters包含字段的集合_id,seq,现在getNextSequence在java中创建函数,这个函数有参数userid作为字符串,所以这样的getNextSequence函数:

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");

}

上面的函数返回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,在counters集合包含其中包含三个文件name为Sarah C. and Bob D.我们手动插入第一次分别与一个默认文档,并将其增加seq这样的{ "_id" : "userid", "seq" : 2 }