如何在 mongodb 的数组顶部添加一个值?

how do i add a value to the top of an array in mongodb?(如何在 mongodb 的数组顶部添加一个值?)

问题描述

如何在 mongodb 的数组顶部添加一个值?

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

假设我的 mongo 收藏中有此文档:

say i have this document in my mongo collection:

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

如何在列表前面添加黄色"?

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

当我这样做时:

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

我会得到这个:

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

我想要这个:

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

提前致谢！

推荐答案

"unshift" 在数组的前面插入数据.. 而"push" 在末尾插入数据.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，Mongo API 不支持将其作为原子操作:

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

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

它只支持推送"

您的阵列有多大?

你可以假设你在 Mongo 中的数组总是反向存储，并使用 push，或者你可以读出数组，用 unshift 修改它，然后再次存储它(虽然这不是原子的)

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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