c# - parent 和 child 的 Linq 订单

Question

我有两个表:反馈和评论。一个反馈可以有很多评论。基本上是一个简单的父子关系。

我有一个页面可以列出所有反馈和相关评论，如下所示:

Feedback AComment A1Comment A2Feedback BComment B1Feedback C (note: no comments)

Each feedback and comments have a created date. At the moment I order by feedback date and then comment date so I always have the newest feedback in the top and then all comments after that.

What I'm trying to achieve is: when a new comment is added to a feedback this feedback should be displayed in the top, no matter how old the feedback is or if a feedback is added without comments this feedback should now be the first item in the list. Let's say a comment is added to Feedback B and after that a new feedback with no comments is added, then my list would look like this:

Feedback D (this is the new feedback)Feedback BComment B1Comment B2 (this is the new comment)Feedback AComment A1Comment A2Feedback C (note: no comments)

Now Feedback D would be in the top of the list because it has the newest date of all feedback and comments and Feedback B would be second as it has Comment B2 which would have the second newest date.

This is my code so far:

_repositories.Feedback
.Include(f => f.Comments)
.OrderByDescending(f => f.PublishedDate);

我想修改

.OrderByDescending(f => f.PublishedDate)

得到正确的顺序。这可能吗？

Answer 1

为每个反馈选择最后评论日期并按它们排序:

_repositories.Feedback
.Include(f => f.Comments)
.OrderByDescending(f => 
    f.Comments
    .Select(c => (DateTime?)c.PublishedDate)
    .OrderByDescending(c => c)
    .FirstOrDefault() ?? f.PublishedDate
)
.ThenByDescending(f => f.PublishedDate);