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']...
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...
{ a : { $exists : false } } 不存在 a IN (1,2,3) 存在 { a : { $in: [1, 2, 3] } } 存在$in:存在 并 并在指定的数组中不存在 $nin:不存在 或 不在指定的数组中 聚合查询: MongoDB聚合框架(Aggregation Framework)是一个计算框架,它可以: 可作用在一个 或 几个集合上 对集合中的数...
Check if a file exist by passing options (at least an_idorfilename) to theexist()method. gfs.exist(options,function(err,found){if(err)returnhandleError(err);found?console.log('File exists'):console.log('File does not exist');}); ...
"idKey": <_id key value>, // The _id value of the document. Only present if an ``_id`` index exists. "indexKey" : { // The missing index entry "<key1>" : <value>, ... } } ... ] 注意 对于missingIndexEntries数组,idKey字段大小及其所有indexKey字段大小总和的上限为 1MB,其中...
The option exists for compatibility and clarity. Disables the preallocation of data files. --nssize <value> Default: 16 Specifies the default size for namespace files, which are files that end in .ns. Each collection and index counts as a namespace. Use this setting to control size for ...
If we only want to find keys whose value is null, we can check that the key is null and exists using the "$exists" conditional: > db.c.find({"z" : {"$in" : [null], "$exists" : true}}) Unfortunately, there is no "$eq" operator, which makes this a little awkward, but "...
For monitoring a MongoDB cluster or stand-alone with Instana, configure--bind_ipwith specific IP addresses or leave it unset to the default value 127.0.0.1. Do not use thebind_ip_allparameter. MongoDB Atlas support Instana agent supports remote monitoring of MongoDB Atlas clusters residing in...
(Windows systems use the \data\db directory.) If you installed using a package management system. Check the /etc/mongodb.conf file provided by your packages to see the configuration of the dbpath. --diaglog <value> Creates a very verbose, diagnostic log for troubleshooting and recording ...
For more information check http://laravel.com/docs/eloquent#soft-deletingMongoDB specific operatorsExistsMatches documents that have the specified field.User::where('age', 'exists', true)->get();AllMatches arrays that contain all elements specified in the query.User::where('roles', 'all', [...