如何用两个联接表a和B的列表编写linq查询，然后按a的ID分组，并从B联接行数

Question

How to write Linq query with list of two joined tables A and B, then grouped by id of A, and with amount of joined rows from B

For example

class A{
   int Id,
   int BId,
   string AName
};

class B{
   int Id,
   string description
};

And to display as follows (after joins of A with B) A.Bid = B.Id

A Id |  count(Id) | AName

Frankly, I have to implement following query from PHP to LINQ. All dependencies are written in query below:

select("asset.id as Id,asset.AssetBundleID as AssetBundleID,asset.GUID as GUID,asset.Name as Id,asset.Name as Id, asset.DisplayName as DisplayName,asset.Description as Description, asset.Category as Category,asset.TexturesSize as TexturesSize, asset.TexturesFileSize as TexturesFileSize, asset.OthersSize as OthersSize, asset.id as Id, asset.OthersFileSize as OthersFileSize, count(*) as InstancesCount")
->from("asset")
->join('Left Join',"assetinstance"," assetinstance . AssetId = asset . Id ")
->groupBy("asset.Id")

Answer 1

Did you mean something like this?

using System;
using System.Collections.Generic;
using System.Linq;

public class A 
{
    public int Id {get; set;}
    public int BId {get; set;}
    public string AName {get; set;}
}

public class B{
    public int Id {get; set;}
    public string description{get; set;}
}


public class Program
{
    private static List<A> _aList = new List<A>();  
    private static List<B> _bList = new List<B>();  

    public static void Main()
    {
        Seed();

        var query =
            from b in _bList
            group b by b.Id into g
            join a in _aList on g.FirstOrDefault().Id equals a.BId         
            select new { A_ID = a.Id, Cnt = g.Count(), AName = a.AName};

        Console.WriteLine("A_ID | count(Id) | AName");
        foreach(var row in query) 
        {
            Console.WriteLine(string.Join(" | ", new string[]{row.A_ID.ToString(), row.Cnt.ToString(), row.AName}));
        }
    }

    public static void Seed() 
    {       
        _aList.Add(new A{Id=1, BId=1, AName="A1"});
        _aList.Add(new A{Id=2, BId=1, AName="A2"});
        _aList.Add(new A{Id=3, BId=1, AName="A3"});
        _aList.Add(new A{Id=4, BId=2, AName="A4"});

        _bList.Add(new B{Id=1, description="B1"});
        _bList.Add(new B{Id=2, description="B2"});
    }
}

See my fiddle https://dotnetfiddle.net/NlAX5V

Answer 2

var result= (from A in ListA
             join B in List B
             on A.ID equals B.ID
             select new {A,B})
             .GroupBy(x=>x.A.Id)
             .Select(x=>new
              {
                ID=x.Key
                count=x.Count(),
                AName=x.Select(z=>z.A.AName)
              }).ToList();