MongoDB的push和root的C#等效项是什么? [英] What is the C# equivalent of push and root for MongoDB?

问题描述

我有很多人.我正在尝试为每个名字找到年龄最大的人.我可以使用mongoDB控制台命令实现该结果

I have a collection of people. I am trying to find the oldest person for each name. I am able to achieve that result using the mongoDB console command

db.People.aggregate([
    { '$sort': { 'Name': 1, 'Age': -1 } }, 
    {       
        '$group': {
            '_id': '$Name',
            'docs': { '$push': '$$ROOT' },
        }
    },
    {
        '$project': {
            'top_one': { 
                '$slice': ['$docs', 1]
            }
        }
    } ])

对于C#驱动程序，这等效于什么?我特别遇到麻烦了

What is the equivalent of this for the C# driver? I'm specifically having trouble with

'docs': { '$push': '$$ROOT' },

这是我当前的C#查询:

Here is my current C# query:

collection.Aggregate(aggArgs)
   .SortByDescending(x => x.Age) 
   .Group(x => x.Name, x => new { 
       Name = x.First().Name, 
       FavoriteColor = x.First().FavoriteColor, 
       FavoriteFood = x.First().FavoriteFood
    }).ToListAsync().Result;

它的工作原理与我的mongo console命令差不多，但是我真的不喜欢构造匿名对象.我更愿意做Group(x => x.Name,x => x.First())，但是会抛出异常，并且不支持"First()".我相信部分问题是我的Person类型没有ID，因此_id放在实际的mongo文档中(插入时由mongo自动执行).当它尝试返回该类型时，无法进行直接映射.

It works close to what my mongo console command does, but I really don't like constructing an anonymous object. I would prefer to do Group(x => x.Name,x => x.First()), but that throws and exceptions that "First()" is not supported. I believe part of the problem is that is that my Person type doesn't have an ID, so _id is put on the actual mongo document (automatically by mongo on insert). When it trys to go back in to the type, it can't do a direct mapping.

因此，考虑到两个版本的查询，如何在不使用每个字段拼写的情况下将我的完整类型恢复为C#?

So, with the two versions of the query in mind, how do I get my full type back in C# without having to spell out EVERY field?

推荐答案

这是MongoDB驱动程序的功能.它不接受简单的First()，它后面需要一些东西.那就是我通过调试看到的.因此，您应该继续使用First()...，也可以直接查询json:

It's a feature of MongoDB driver. It doesn't accept simple First(), it need something behind it. That was what i have seen by debugging. So you should either continue to work with First()... or you could query your json directly:

var result = collection.Aggregate()                
        .Group(new JsonProjectionDefinition<People>(@" {
              '_id': '$Name',
               'docs': { '$push': '$$ROOT' },}"))
        .Project<TopOne>(new JsonProjectionDefinition<BsonDocument>(@"{
            'top_one': { 
            '$slice': ['$docs', 1]
        } }"))
       .ToList();

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