mongos> var it = db.test.find({'i': 1, "old_id": {$exists: 1}}) 遍历计数1:mongos> var count = 0;while(it.hasNext()){if (it.next()["X"].length==32)++count}print(count) 遍历计数2:mongos> var count = 0;while(it.hasNext()){var item = it.next(); if (item['X']...
const{MongoClient}=require('mongodb');asyncfunctioncheckDocumentExists(collectionName,query){consturi="mongodb://localhost:27017";// MongoDB 连接字符串constclient=newMongoClient(uri);try{awaitclient.connect();// 连接到 MongoDBconstdatabase=client.db('testDB');// 选择数据库constcollection=databa...
= keys.end(); i++ ) { if( ++n == 2 ) { d->setIndexIsMultikey(idxNo);//设置多键值索引 } assert( !recordLoc.isNull() ); try { idx.head/*DiskLoc*/.btree()/*BtreeBucket*/->bt_insert(idx.head, recordLoc, //执行向btree中添加记录和绑定索引信息的操作 *i, ordering, dupsAll...
{<key>:{$type:<value>}}类型比较,Mongodb中存在的类型。 db.col.find({"title" : {$type : 'string'}}) $exists {<key>:{$exists:<value>}}字段是否存在。 db.col.find( { item : { $exists: false } } ) 模糊查询 没有操作符,根据书写规则来决定是否是模糊查询。 和普通is查询一样,但是...
db.runCommand(cmdObj) run a database command. if cmdObj is a string, turns it into {cmdObj:1} db.setProfilingLevel(level) 0=off,1=slow,2=all db.shutdownServer() 关闭当前服务程序 db.version() 返回当前程序的版本信息 数据集(表)操作语法 ...
if true , the mongod instance performs the availability check and only continues to start up if the ldap server is available. if false , the mongod instance skips the availability check; i.e. the instance starts up even if the ldap server is unavailable. --ldapqueryuser <string> ...
MongoDB 的主要目标是在 key-value (键/值)存储方式(提供了高性能和高度伸缩性)以及传统的 RDBMS 系统(丰富的功能)架起一座桥梁,集两者的优势于一身。 MongoDB 适用范围如下:网站数据: Mongo 非常适合实时的插入,更新与查询,并具备网站实时数据存储所需的复制及高度伸缩性。 **缓存:**由于性能很高, Mongo 也...
ChunkRange(_args.getMinKey(), _args.getMaxKey()), _chunkVersion, _args.getWaitForDelete()); _state=kCloning; }if(replEnabled) { autoconstreadConcernArgs =repl::ReadConcernArgs( replCoord->getMyLastAppliedOpTime(), repl::ReadConcernLevel::kLocalReadConcern);//检查当前节点状态是否满足repl:...
{'$exists': true}}).count() CREATE INDEX myindexname ON users(name) db.users.ensureIndex({name:1}) CREATE INDEX myindexname ON users(name,ts DESC) db.users.ensureIndex({name:1,ts:-1}) EXPLAIN SELECT * FROM users WHERE z=3 db.users.find({z:3}).explain() UPDATE users SET a=...
if true , the mongod instance performs the availability check and only continues to start up if the ldap server is available. if false , the mongod instance skips the availability check; i.e. the instance starts up even if the ldap server is unavailable. --ldapqueryuser <string> ...