MongoDB C++ 數組的寫操作

經常會碰到這類問題，現在將前兩年自己寫過的代碼總結一下，以後編程會方便很多。

Document中包含兩個數組，一個簡單點，每個元素都是string，一個復雜點，每個元素都是一個對象，有兩個屬性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++代碼如下：

這個函數填充簡單的數組，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();
}

第二個函數添加了較復雜的數組，同時演示了update方法的使用。這個方法，假定receivers數組還不存在，采用$set命令進行設置。

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());
}
}

再復雜點。現在想修改一下address為00...20的那個元素的status="sending"。具體原理參考：

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

下面演示JavaScript代碼：

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")
}

$ 這是個占位符，表示第一個被找到的數組元素。文檔：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++代碼來了：

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());
}