Linq GroupBy并选择其他属性作为列表

问题描述

如何使用LINQ按属性分组并选择其他属性作为列表?

How to group by Properties and select other properties as lists using LINQ?

我不擅长解释，所以这里有一个例子:

I'm bad at explaining it so here's an example:

让我们说我有一个C#对象列表，可以像这样用JSON表示:

Lets say I have a list of C# objects that can be represented in JSON like this:

[
    { "id":123, "name":"John", "carId":1, "carAge":3 },
    { "id":123, "name":"John", "carId":2, "carAge":4 },
    { "id":4, "name":"Mary", "carId":3, "carAge":3 },
    { "id":4, "name":"Mary", "carId":4, "carAge":3 },
    { "id":123, "name":"John", "carId":5, "carAge":3 }
]

在所有这些对象中，只有 carId 是唯一的.

Among all those objects only carId is unique.

我想按人员详细信息对它们进行分组，并将这些详细信息与相连的汽车详细信息合并.

I would like to group them by person details and join those details with connected car details.

最终结果如下所示，但作为c#对象:

The end result would look like this but as c# objects:

[
    {"id":123, "name":"John",
        [
            {"carId":1, "carAge":3},
            {"carId":2, "carAge":4},
            {"carId":5, "carAge":3}
        ]
    },
    {"id":4, "name":"Mary",
        [
            {"carId":3, "carAge":3},
            {"carId":4, "carAge":3}
        ]
    }
]

我被困在

list.GroupBy(x => new { x.Id, x.Name })

因为我不需要任何聚合函数，而只需要选择即可.

because I don't need any aggregate functions but only selection.

很抱歉没有发布更多代码，这是一个简化的版本，真实内容具有更多过滤和复杂的领域特定术语.

I apologize for not posting more code, this is a simplified version, the real thing has more filtering and convoluted domain specific terminology.

一切都在内存中完成-无需担心DB.

Everything is done in memory - without DB to worry about.

推荐答案

为 group _ by _ 表达式的每个部分创建一个具有所需字段的匿名对象.

for each section of the group _ by _ expression create an anonymous object with the fields you want.

通过以下任何一种方式，您将为每个键构造一个嵌套集合-使用 GroupBy 时，它不仅涉及聚合，而且还涉及对特定数据组的操作.一种情况是聚合方法.

With any of the following ways you will construct a nested collection for each of your keys - when using a GroupBy it is not just about aggregations but about operations on specific groups of data. One case of it is aggregation methods.

var result = from item in data
             group new { item.carId, item.carAge }  by new {item.id, item.name} into g
             select g;

另一种方法是

var result = from item in data
             group  by new {item.id, item.name} into g
             select new {
                 g.Key,
                 Data = g.Select(i => new {i.carId, i.carAge})
             };

---

使用您尝试使用的方法语法，可以使用以下重载:

---

Using method syntax as you tried you can use the following overload:

var result = data.Group(k => new {k.id, k.name},
                        e => new {e.carId, e.carAge});

或者如果不是，只需添加一个 Select 进行投影:

Or if not the just add a Select for projection:

var result = data.Group(k => new {k.id, k.name})
                 .Select(g => new {
                     g.Key,
                     Data = g.Select(i => new {i.carId, i.carAge})
                 });

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