循环遍历所有 Mongo 集合并执行查询

本文介绍了循环遍历所有 Mongo 集合并执行查询的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

首先，我对 mongodb 很陌生.这是我一直无法找到解决方案的问题.

First of, I'm quite new to mongodb. Here's my question I've not been able to find a solution to.

假设我有 3 个不同的集合.

Let's say I have 3 different collections.

mongos> show collections collectionA collectionB collectionC

我想创建一个脚本来迭代这个数据库中的所有集合，并在每个集合中找到最后插入的时间戳.以下是 mongos 的工作原理.

I want to create a script that iterates over all collections ind this database and find the last inserted timestamp in each of these collections. Here's what works inside mongos.

var last_element = db.collectionA.find().sort({_id:-1}).limit(1); printjson(last_element.next()._id.getTimestamp()); ISODate("2014-08-28T06:45:47Z")

1.问题(迭代所有集合)

有没有可能……喜欢.

var my_collections = show collections; my_collections.forEach(function(current_collection){ print(current_collection); });

问题在这里，my_collections 的赋值不起作用.我得到 SyntaxError: Unexpected identifier.我需要引用'show'声明吗?甚至有可能吗?

Problem here, the assignment for my_collections does not work. I get SyntaxError: Unexpected identifier. Do I need to quote the 'show' statement ? Is it even possible ?

2.问题(在 js var 中存储集合)

我可以通过这样做来解决问题 1:

I can workaround Problem 1 by doing this:

var my_collections = ["collectionA", "collectionB", "collectionC"]; my_collections.forEach(function(current_collection){ var last_element = db.current_collection.find().sort({_id:-1}).limit(1); print(current_collection); printjson(last_element.next()._id.getTimestamp()); });

last_element.next() 产生以下错误:

error hasNext: false at src/mongo/shell/query.js:124

error hasNext: false at src/mongo/shell/query.js:124

last_element 似乎没有正确保存.

It seems that last_element isn't saved correctly.

对我做错了什么有什么建议吗??

Any suggestions on what I'm doing wrong??

更新

Neils 的回答让我找到了这个解决方案.除了他的代码之外，我还必须检查函数 getTimestamp 是否真的存在.对于某些虚拟"集合，似乎没有 _id 属性.

Neils answer lead me to this solution. In addition to his code I had to check if the function getTimestamp really exist. For some 'virtual' collections there seem to be no _id property.

db.getCollectionNames().forEach(function(collname) { var last_element = db[collname].find().sort({_id:-1}).limit(1); if(last_element.hasNext()){ var next = last_element.next(); if(next._id !== undefined && typeof next._id.getTimestamp == 'function'){ printjson(collname + " >> "+next._id.getTimestamp()); }else{ print(collname + " undefined!! (getTimestamp N/A)") } } });

推荐答案

db.getCollectionNames() 辅助方法可以为您执行此操作.然后你可以实现你的代码:

There is the db.getCollectionNames() helper method that does this for you. You can then implement your code:

db.getCollectionNames().forEach(function(collname) { // find the last item in a collection var last_element = db[collname].find().sort({_id:-1}).limit(1); // check that it's not empty if (last_element.hasNext()) { // print its timestamp printjson(last_element.next()._id.getTimestamp()); } })

您可能还需要一个 .hasNext() 签入以处理可能的空集合.

You probably also want a .hasNext() check in there to cater for possible empty collections.