LINQ嵌套連接三個表

Question

我有以下代碼：

var configItems = new List<ConfigurableItem>(); 
var assemblies = new List<Assembly>(); 
var pcbas = new List<Pcba>(); 

configItems.Add(new ConfigurableItem() { CiCode = "TST001", AssemblyId = "ASS001" }); 
configItems.Add(new ConfigurableItem() { CiCode = "TST002", AssemblyId = "ASS001" }); 
configItems.Add(new ConfigurableItem() { CiCode = "TST003", AssemblyId = "ASS002" }); 
configItems.Add(new ConfigurableItem() { CiCode = "TST004", AssemblyId = "ASS003" }); 

assemblies.Add(new Assembly { AssemblyId = "ASS001", PcbaId = "PCBA001"}); 
assemblies.Add(new Assembly { AssemblyId = "ASS002", PcbaId = "PCBA002" }); 

pcbas.Add(new Pcba { PcbaId = "PCBA001", Pcb = "401"}); 

var query = from c in configItems 
      join ca in (from a in assemblies join p in pcbas on a.PcbaId equals p.PcbaId into ca from x in ca.DefaultIfEmpty() select a) 
      on c.AssemblyId equals ca.AssemblyId into cap 
      from ca in cap.DefaultIfEmpty() 
      select new { 
       CiCode = c.CiCode, 
       AssemblyId = (ca == null ? "-" : ca.AssemblyId), 
       Pcb = ??? 
      }; 

我怎樣才能讓LINQ查詢產生以下結果集：

TST001 | ASS001 | PCBA001 | 401 
TST002 | ASS001 | PCBA001 | 401 
TST003 | ASS002 | -  | - 
TST004 | - | -  | - 

Answer 1

這可能有助於

from c in configItems 
    join ca in (from a in assemblies join p in pcbas on a.PcbaId equals p.PcbaId into ca from x in ca.DefaultIfEmpty() select new {a,x}) 
      on c.AssemblyId equals ca.a.AssemblyId into cap 
      from ca in cap.DefaultIfEmpty() 
      select new { 
       CiCode = c.CiCode, 
       AssemblyId = (ca == null ? "-" : ca.a.AssemblyId), 
       Pcb = (ca != null && ca.x != null) ?ca.x.Pcb :"-", 

      } 

Here is working example