你可以让 mongo $push prepend 而不是 append 吗? [英] Can you have mongo $push prepend instead of append?

问题描述

当我执行 mongo $push 时，我希望在我的集合的开头添加 push add，而不是附加到末尾.

I'd like to have push add at the beginning of my set rather than appended to the end when I do a mongo $push.

是否可以进行原子推送更新，将元素添加为第一个而不是最后一个?

Is it possible to do an atomic push update that adds elements as the first rather than the last?

2014 年更新:是的，你可以.

推荐答案

从 MongoDB v2.5.3 开始，有一个新的 $position 运算符，您可以将其与 $each 运算符作为 $push 查询的一部分，用于指定数组中要插入值的位置.

As of MongoDB v2.5.3, there is a new $position operator that you can include along with the $each operator as part of your $push query to specify the location in the array at which you would like to insert a value.

这是文档页面中的示例，用于在数组索引 2 处添加元素 20 和 30::

Here's an example from the docs page to add the elements 20 and 30 at the array index of 2::

db.students.update( { _id: 1 },
                    { $push: { scores: {
                                         $each: [ 20, 30 ],
                                         $position: 2
                                       }
                             }
                    }
                  )

参考:http://docs.mongodb.org/master/reference/operator/update/position/#up._S_position

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