LINQ Lambda，集团列表 [英] LINQ Lambda, Group by with list

问题描述

使用LINQ（Lambda Expression）到.GroupBy数据可以使用正确的语法，而不是使用通常的.Sum（）或.Count（）我希望生成的数据是一个Int的列表。

我定义了我自己的类名为Filter_IDs。它的构造函数需要两个参数：

  public int？类型; //表示数据库中的object_type列
 public List< int？>对象; //表示从我的数据库中的object_id列
  

我想将数据库中的数据加载到此对象中。以下LINQ查询应导致Filter_ID列表：

以下LINQ查询应导致Filter_ID列表：

 列表< Filter_IDs> filterids = ef.filterLine 
 .GroupBy（fl => fl.objectType）
 .Select（fl => new Filter_IDs {type = fl.Key，objects = fl.Select（x => x.object_id）.ToList（）}）
 .ToList（）; 
  

使用此查询不会导致构建错误，但在RunTime上提供NotSupportedException。

数据库看起来像这样可以更好地了解数据：

http://d.pr/i/mnhq+ （droplr image）

提前感谢，
Gerben

解决方案

我认为问题是DB无法在select中调用ToList，也不能创建一个新的Filter_ID。

尝试这样：

 列表< ; Filter_IDs> filterids = ef.filterLine.Select（o => new {objectType = o.objectType，object_id = o.object_id} 
 .GroupBy（fl => fl.objectType）.ToList（）
 。选择（fl => new Filter_IDs {type = fl.Key，objects = fl.Select（x => x.object_id）.ToList（）}）
 .ToList（）; 
  

I'm having some trouble with finding the right syntax to accomplish the following:

Is it possible with LINQ (Lambda Expression) to .GroupBy data and instead of using the usual .Sum() or .Count() I want the resulting data to be a List of Int.

I defined my own class named: Filter_IDs. Its constructor needs two parameters:

public int? type; // Represents the object_type column from my database
public List<int?> objects; // Represents the object_id column from my database

I want to load data from my database into this object. The following LINQ query should result in a List of Filter_IDs:

The following LINQ query should result in a List of Filter_IDs:

List<Filter_IDs> filterids = ef.filterLine
        .GroupBy(fl => fl.objectType)
    .Select(fl => new Filter_IDs { type = fl.Key, objects = fl.Select(x => x.object_id).ToList() })
    .ToList();

Using this query gives no building error but gives an 'NotSupportedException' on RunTime.

The database looks like this to give you a better understanding of the data:

http://d.pr/i/mnhq+ (droplr image)

Thanks in advance, Gerben

解决方案

I think the problem is the DB is not able to call ToList in the select, nor to create a new Filter_ID.

Try something like this :

List<Filter_IDs> filterids = ef.filterLine.Select(o => new { objectType = o.objectType, object_id=o.object_id})
    .GroupBy(fl => fl.objectType).ToList()
    .Select(fl => new Filter_IDs { type = fl.Key, objects = fl.Select(x => x.object_id).ToList() })
    .ToList();

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