java - Spring 数据 MongoDB : aggregation framework - sort with nested property throws invalid reference

Question

我找到了 this article in Spring Forum这显然部分讨论了相同的问题，但没有回答我的问题。

给定以下文档...

{
    "_id": { "$oid": "5214b5d529ee12460939e2ba"},
    "title": "this is my title",
    "tags": [ "fun", "sport" ],
    "comments": [
        {
            "author": "alex",
            "text": "this is cool",
            "createdAt": 1
        },
        {
            "author": "sam",
            "text": "this is bad",
            "createdAt": 2
        },
        {
            "author": "jenny",
            "text": "this is bad",
            "createdAt": 3
        }
    ]
}

...我想做这个聚合(Javascript)...

//This is as concise as possible to focus on the actual problem which is the sort operation when ported to Spring!  
db.articles.aggregate( 
    {$unwind:"$comments"},
    //do more like match, group, etc...
    {$sort:{"comments.createdAt":-1}} //Sort descending -> here the problem occurs in Spring (works in Javascript!)
);

...但是使用 Spring -> 抛出无效引用!

Aggregation agg = newAggregation(
       unwind("comments"),
       sort(Direction.DESC, "comments.createdAt") //Throws invalid reference 'comments.createdAt'!
       //How can I make this work? 
);

当然，我可以使用 native Java 驱动程序而不使用 Spring 的 MongoTemplate 来完成它，但我不太喜欢这种方法。我该怎么做才能使这种精确聚合与 Spring 一起工作？

我使用的是当前版本 1.4.0.RELEASE。

Answer 1

发布的代码确实可以成功运行 - 我遇到的问题是其他问题。

我做了这样的事情:

Aggregation agg = newAggregation(
       project("comments"), //This was the problem! Without this it works as desired!
       unwind("comments"),
       sort(Direction.DESC, "comments.createdAt") 
);

正如我在代码中所写的那样，我只想投影评论 - 字段以节省一些开销 - 但这实际上导致了我的问题!

非常感谢您的提示!