使用自定义表达式或函数对MongoDB进行排序 [英] MongoDB sort with a custom expression or function

问题描述

我的一个收藏夹是具有某些状态的一系列操作(或任务).例如，文档列表看起来像这样

One of my collections is a list of operations (or tasks) with some status. For example, a list of documents can look like this

{
  _id: '57befe57fc956d2e3252890c',
  task: 'Go buy milk',
  status: 'pending'
},
{
  _id: '57befe5efc956d2e3252890d',
  task: 'Cook dinner',
  status: 'complete'
},
{
  _id: '57befe5efc956d2e3252890e',
  task: 'Play games',
  status: 'new'
}

我想根据其状态对列表进行排序，其中new > pending > complete.

I want to sort this list based on a their status, where new > pending > complete.

如何在不创建额外字段的情况下使用MongoDB做到这一点?我问的是，在我的情况下，排序顺序可能是预先配置的(例如，用户可以将其偏好设置为pending > new > complete)

How can I do that with MongoDB without having to create an extra field? I am asking as in my case the sorting order may be pre-configured (i.e. users could have their preferences to pending > new > complete for example)

推荐答案

基于@chirdam所说的是实现的样子.同样，新排序的字段也不按要求出现在结果中.

Based on what @chirdam said here is what the implementation looks like. Also the new sorted field is not present in the result as requested.

数据集:

{
  _id: '57befe57fc956d2e3252890c',
  task: 'Go buy milk',
  status: 'pending'
},
{
  _id: '57befe5efc956d2e3252890d',
  task: 'Cook dinner',
  status: 'complete'
},
{
  _id: '57befe5efc956d2e3252890e',
  task: 'Play games',
  status: 'new'
}

查询:

db.task.aggregate([
    { "$project" : {
        "_id" : 1,
        "task" : 1,
        "status" : 1,
        "order" : {
            "$cond" : {
                if : { "$eq" : ["$status", "new"] }, then : 1,
                else  : { "$cond" : {
                    "if" : { "$eq" : ["$status", "pending"] }, then : 2, 
                    else  : 3
                    }
                }
            }
        }
    } }, 
    {"$sort" : {"order" : 1} },
    { "$project" : { "_id" : 1, "task" : 1, "status" : 1 } }
])

输出:

{ "_id" : "57befe5efc956d2e3252890e", "task" : "Play games", "status" : "new" }
{ "_id" : "57befe57fc956d2e3252890c", "task" : "Go buy milk", "status" : "pending" }
{ "_id" : "57befe5efc956d2e3252890d", "task" : "Cook dinner", "status" : "complete" }

这篇关于使用自定义表达式或函数对MongoDB进行排序的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！