[英]var usage in mongoDB
I am learning mongoDB by following the tutorial, http://docs.mongodb.org/manual/tutorial/getting-started/ 我通过遵循http://docs.mongodb.org/manual/tutorial/getting-started/教程来学习mongoDB。
However, the sample code, var c = db.testData.find()
, confuses me. 但是,示例代码
var c = db.testData.find()
使我感到困惑。 Without var, the execution just prints out the documents, with the var, c becomes the cursor. 如果没有var,则执行仅打印出文档,而使用var,c成为光标。 The other command,
j = { name : "mongo" }
, I don't see the difference with or without var. 另一个命令
j = { name : "mongo" }
,无论是否带有var,我都看不到区别。 I want to be clear when I should have var and when I can ignore var. 我想弄清楚何时应该使用var,何时可以忽略var。
I google the question little bit, for example, Difference between using var and not using var in JavaScript , it talks about scope. 我在谷歌上搜索了一点问题,例如, 在JavaScript中使用var和不使用var之间的区别 ,它讨论了范围。 I cannot understand how my question relates to scope.
我不明白我的问题与范围的关系。
http://docs.mongodb.org/manual/tutorial/iterate-a-cursor/ http://docs.mongodb.org/manual/tutorial/iterate-a-cursor/
According to this doc, 根据这份文件,
However, in the mongo shell, if the returned cursor is not assigned to a variable using the var keyword, then the cursor is automatically iterated up to 20 times to print up to the first 20 documents in the results.
但是,在mongo shell中,如果未使用var关键字将返回的游标分配给变量,则该游标将自动迭代多达20次,以打印结果中的前20个文档。
From the mongo getting started tutorial: 从mongo入门教程:
This tutorial provides an introduction to basic database operations using the mongo shell.
本教程介绍了使用mongo shell进行的基本数据库操作。 mongo is a part of the standard MongoDB distribution and provides a full JavaScript environment with a complete access to the JavaScript language and all standard functions as well as a full database interface for MongoDB.
mongo是标准MongoDB发行版的一部分,它提供了完整的JavaScript环境,可以完全访问JavaScript语言和所有标准功能,以及MongoDB的完整数据库接口。 See the mongo JavaScript API documentation and the mongo shell JavaScript Method Reference.
请参阅mongo JavaScript API文档和mongo shell JavaScript方法参考。
Source: http://docs.mongodb.org/manual/tutorial/getting-started/ 来源: http : //docs.mongodb.org/manual/tutorial/getting-started/
In Javascript it's best practice to not use global variables. 在Javascript中,最佳做法是不使用全局变量。 You define global variables without the
var
prefix and local variables with the var
prefix. 您没有定义全局变量
var
前缀和局部变量var
前缀。 I guess the Javascript implementation in Mongo disabled global variables completely because it's bad practice. 我猜Mongo中的Javascript实现完全禁用了全局变量,因为这是一种不好的做法。
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