如何将值添加到MongoDB中一个阵列的顶部？ [英] how do i add a value to the top of an array in mongodb?

问题描述

我怎么值添加到MongoDB中一个数组的顶部？

how do i add a value to the top of an array in mongodb?

说，我在我的收藏蒙哥这个文件：

say i have this document in my mongo collection:

{ "colors" : [ "red", "green", "blue" ] }

如何添加黄到列表的前面？

how do i add "yellow" to the front of the list?

当我做的：

{$push:{colors:"yellow"}}

我会得到这样的：

i'd get this:

{ "colors" : [ "red", "green", "blue", "yellow" ] }

我想这样的：

{ "colors" : [ "yellow", "red", "green", "blue"] }

在此先感谢！

推荐答案

在一个阵列前端的unshift插入数据..而推插入它的结束。
例如在JavaScript中：

"unshift" inserts data in the front of an array.. whereas "push" inserts it at the end. e.g. in JavaScript:

> a = ['red','green','blue']
[ "red", "green", "blue" ]
> a.unshift("yellow")
4
> a
[ "yellow", "red", "green", "blue" ]

但不幸的是这不是由蒙戈API作为一个原子操作的支持：

But unfortunately this isn't supported by the Mongo API as an atomic operation:

http://www.mongodb.org/display/DOCS/Updating

它只是支持推

你有多大的阵列？

您可以醚假设你在蒙戈阵列总是存储在倒车时，和使用推，或者你可以读出的数组，不印字修改它，然后再存放起来（这不会是原子虽然）

you could ether assume that your array in Mongo is always stored in reverse, and use push, or you could read-out the array, modify it with unshift, and then store it again (which wouldn't be atomic though)

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