MongoDB 排序
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MongoDB sorting
提问by teggy
I want implement a "bump" feature for topics. Once a topic is bumped, it will have a new "bump_date" field. I want to sort it so that when there is a "bump_date" field, it will be sorted as if it was the "created" field. Here's an example of my db.topics:
我想为主题实现“碰撞”功能。一旦主题被碰撞，它将有一个新的“bump_date”字段。我想对它进行排序，以便当有一个“bump_date”字段时，它会被排序，就好像它是“创建”字段一样。这是我的 db.topics 示例：
{
"text" : "test 1",
"created" : "Sun Nov 20 2011 02:03:28 GMT-0800 (PST)"
},
{
"text" : "test 2",
"created" : "Sun Nov 18 2011 02:03:28 GMT-0800 (PST)"
},
{
"text" : "test 3",
"created" : "Sun Nov 17 2011 02:03:28 GMT-0800 (PST)",
"bump_date: : "Sun Nov 19 2011 02:03:28 GMT-0800 (PST)"
}
I want the sort to return in the order of "test 1", "test 3", "test 2"
我希望排序以“测试 1”、“测试 3”、“测试 2”的顺序返回
回答by Brian Hicks
Sorting in MongoDB is done like so:
MongoDB 中的排序是这样完成的：
db.collection.find({ ... spec ... }).sort({ key: 1 })
db.collection.find({ ... spec ... }).sort({ key: 1 })
where 1is ascending and -1is descending.
哪里1是上升和-1下降。
In your specific example: db.topics.find().sort({ bump_date: 1 }), although it might be better to call it something like "updated_at".
在您的具体示例中：db.topics.find().sort({ bump_date: 1 })，尽管将其称为“updated_at”之类的内容可能会更好。
You'll also definitely want to put an index on your "bump_date" field.
您肯定还想在“bump_date”字段上放置索引。
回答by Tyler Brock
As Brian Hicks suggested, creating an additional updated_at field is the way to go. This way, when a document is created you can have created_at and updated_at initially be the same.
正如 Brian Hicks 所建议的，创建一个额外的 updated_at 字段是可行的方法。这样，当创建文档时，您可以使 created_at 和 updated_at 最初相同。
{
"created_at": xxx,
"updated_at": xxx
}
If you then "bump" the updated_at field by setting it to the current time when there is a a bump event you can sort on the updated_at field to achieve the ordering you desire.
如果您然后通过将其设置为当前时间来“碰撞”updated_at 字段，则您可以在发生碰撞事件时对 updated_at 字段进行排序以实现您想要的排序。
回答by Oneide Luiz Schneider
Also:
还：
db.collection.find( { $query: {}, $orderby: { column : -1 } } )
where 1 is ascending and -1 is descending.
其中 1 为升序，-1 为降序。
回答by DhruvPathak
Currently it is not possible in mongodb to do a sort based on user defined criteria over multiple columns.eg. here the function would have been to return bump_dateif it is set,else return created
目前在 mongodb 中不可能根据用户定义的标准对多个列进行排序。例如。这里的函数bump_date如果设置了就返回，否则返回created
Either you will have to use a server-side or client-side code as mentioned here :
您将不得不使用此处提到的服务器端或客户端代码：
or if you want to stay with basic quering and sorting, you shall :
或者，如果您想继续使用基本的查询和排序，您应该：
create a key
bump_dateequivalent tocreatedwhenever a new record is created. This will notbe a data overhead, as you can expect every topic of yours to be bumped once in a while in future,hencebump_datefield will eventually be added. So add it from the start itself.Whenever the article is bumped,update the field
bump_date.
创建一个
bump_date相当于created每当创建新记录时的键。这不会是数据开销，因为您可以预期您的每个主题将来bump_date都会偶尔被碰撞，因此最终会添加字段。所以从一开始就添加它。每当文章被碰撞时，更新该字段
bump_date。
Your example documents will look like this with this change :
通过此更改，您的示例文档将如下所示：
{
"text" : "test 1",
"created" : "Sun Nov 20 2011 02:03:28 GMT-0800 (PST)",
"bump_date" : "Sun Nov 20 2011 02:03:28 GMT-0800 (PST)"
},
{
"text" : "test 2",
"created" : "Sun Nov 18 2011 02:03:28 GMT-0800 (PST)",
"bump_date" : "Sun Nov 18 2011 02:03:28 GMT-0800 (PST)"
},
{
"text" : "test 3",
"created" : "Sun Nov 17 2011 02:03:28 GMT-0800 (PST)",
"bump_date: : "Sun Nov 19 2011 02:03:28 GMT-0800 (PST)"
}
You shall ensureIndexon bump_date field. Now you can query the required data easily.
你应该ensureIndex在bump_date 字段上。现在您可以轻松查询所需数据。
db.topics.find().sort({ bump_date: 1 })
