CouchDb由用户按时间戳降序对帖子进行排序 [英] CouchDb sort posts by a user in descending timestamp order

问题描述

我的帖子中包含用户名（帖子的作者）和时间戳（上传时间）之类的字段。我正在努力创建一个视图，查询该视图时，该视图将按时间戳的降序抓住特定用户的帖子。

I have posts that have fields like username (author of the post) and timestamp (uploaded time). I am struggling to create a view, which when queried on, grabs posts by a particular user in descending order of the timestamp.

map: function(doc) {
    if (doc.type == 'post'){
        emit(doc.username, [doc._id, doc.timestamp]);
    };
},

我可以查询特定用户创作的文档，但如何应用降序= p仅在时间戳字段上为真？

I can query documents authored by a particular user but how do I apply descending = true only on the timestamp field?

推荐答案

对于CouchDB视图，只有键才能确定索引的排序顺序。该值根本不考虑排序/分组。

With CouchDB views, only the key can determine the sort order for the index. The value does not factor into sorting/grouping at all.

因此，如果要创建一个视图，该视图按创建顺序输出用户的帖子（升序或降序） ），您将发出一个数组作为一种复合键。我强烈建议您通读其中的视图指南 CouchDB文档。

Thus, if you want to have a view that outputs posts by a user in order of creation (ascending or descending), you'll emit an array as a sort of "composite key". I would highly recommend reading through the Guide to Views in the CouchDB documentation.

以您的示例为例，我将使地图功能如下：

For your example, I would make a map function like this:

function (doc) {
  if (doc.type === 'post') {
    emit([ doc.username, doc.timestamp ]);
  }
}

然后，您可以获取特定用户的帖子查询如下：

Then, you can get the posts for a specific user with a query like:

?start_key=["username"]&end_key=["username","\ufff0"]

这将找到按时间戳升序排列的给定用户名的帖子。要颠倒顺序，请改用以下查询：

Which will find the posts for the given "username" ordered by the timestamp ascending. To reverse the ordering, use the following query instead:

?start_key=["username","\ufff0"]&end_key=["username"]&descending=true

请注意， start_key 和 end_key 已互换，并添加了 descending = true 。

Note that the values for start_key and end_key have swapped, and descending=true has been added.

如前所述，请仔细阅读他们的文档，因为这是绕过使用CouchDB视图的最佳方法的好方法。

As mentioned before, read through their documentation as it's an excellent way to wrap your head around the best way to use CouchDB views.

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