MongoDB C++ 数组的写操作

经常会碰到这类问题，现在将前两年自己写过的代码总结一下，以后编程会方便很多。

Document中包含两个数组，一个简单点，每个元素都是string，一个复杂点，每个元素都是一个对象，有两个属性address和status.

> db.schedule.findOne({"_id" : ObjectId("51e930f92291307bb05a1a84")}){"_id" : ObjectId("51e930f92291307bb05a1a84"),"direction" : 2,"messages" : ["m1","m2","m3"],"receivers" : [{"address" : "000000000020","status" : "waiting"},{"address" : "000000000018","status" : "waiting"}],"speed" : 3,"start_time" : "1374236921","stay_time" : 1,"user_id" : ObjectId("518b7fc5117e87bce28f2444")}

c++代码如下：

这个函数填充简单的数组，用到了BSONArrayBuilder. 注意其演示了insert方法的使用。

string AddScheduledMessage(ScheduledMessage const& m) {  shared_ptr<mongo_session> mongo_session = mongo_session_factory::get_session();  BSONObjBuilder data_builder;  OID _id = OID::gen();  data_builder.append("_id", _id);  data_builder.append("user_id", mongo::OID(m.user_id));  data_builder.append("start_time", m.start_time);  data_builder.append("direction", m.direction);  data_builder.append("speed", m.speed);  data_builder.append("stay_time", m.stay_time);  BSONArrayBuilder msgs_builder;  size_t size = m.msgs.size();  for (size_t i = 0; i < size; ++i) {    msgs_builder.append(m.msgs[i]);  }  data_builder.append("messages", msgs_builder.arr());  mongo_session->get().insert("db.schedule", data_builder.obj());  return _id.str();}

第二个函数添加了较复杂的数组，同时演示了update方法的使用。这个方法，假定receivers数组还不存在，采用$set命令进行设置。

void AssignScheduledMessages(ScheduledMessages & ms) {  shared_ptr<mongo_session> mongo_session = mongo_session_factory::get_session();  vector<shared_ptr<ScheduledMessage> >::iterator itor, last = ms.values.end();  for (itor = ms.values.begin(); itor != last; ++itor) {    shared_ptr<ScheduledMessage> m = *itor;    BSONObjBuilder condition;    condition.append("user_id", OID(m->user_id));    condition.append("_id", OID(m->id));    BSONArrayBuilder arr_builder;    size_t size = m->receivers.size();    for (size_t i = 0; i < size; ++i) {      BSONObjBuilder rec;      rec.append("address", m->receivers[i]->address);      rec.append("status", m->receivers[i]->status);      arr_builder.append(rec.obj());    }    BSONObjBuilder recs;    recs.append("receivers", arr_builder.arr());    BSONObjBuilder set;    set.append("$set", recs.obj());        mongo_session->get().update("db.schedule", mongo::Query(condition.obj()), set.obj());  }}

再复杂点。现在想修改一下address为00...20的那个元素的status="sending"。具体原理参考：

http://stackoverflow.com/questions/9247007/mongodb-update-the-specific-element-from-subarray

下面演示JavaScript代码：

db.schedule.update({"_id" : ObjectId("51e930f92291307bb05a1a84"), "receivers": {$elemMatch: {"address": "000000000020"}}}, {$set: {"receivers.$.status": "sending"}})> db.schedule.findOne(){"_id" : ObjectId("51e930f92291307bb05a1a84"),"direction" : 2,"messages" : ["m1","m2","m3"],"receivers" : [{"address" : "000000000020","status" : "sending"},{"address" : "000000000018","status" : "waiting"}],"speed" : 3,"start_time" : "1374236921","stay_time" : 1,"user_id" : ObjectId("518b7fc5117e87bce28f2444")}

$ 这是个占位符，表示第一个被找到的数组元素。文档：http://docs.mongodb.org/manual/core/update/#array

NameDescription$Acts as a placeholder to update the first element that matches the query condition in an update.C++代码来了：

void SaveScheduleMessageStatus(string const& message_id, string const& address, string const& status) {  shared_ptr<MongoSession> mongo_session = MongoSessionFactory::GetSession();  BSONObjBuilder condition;  condition.append("_id", OID(message_id));  BSONObjBuilder con1;  con1.append("address", address);      BSONObjBuilder con2;  con2.append("$elemMatch", con1.obj());  condition.append("receivers", con2.obj());  BSONObjBuilder recs;  recs.append("receivers.$.status", status);  BSONObjBuilder set;  set.append("$set", recs.obj());      mongo_session->GetDBClientBase().update("db.schedule", mongo::Query(condition.obj()), set.obj());}