Linq內部聯接復雜查詢

Question

var workbasketitems = new[] { //workbasketitems
    new { TaskId = 10, WorkGroupId = 100, ActionUserId =1000, Work = "item 0" },
    new { TaskId = 11, WorkGroupId = 101, ActionUserId =1001, Work = "item 1" },
    new { TaskId = 12, WorkGroupId = 102, ActionUserId =1002, Work = "item 2" }
};
var workflowtasks = new[] { //workflowtasks
    new { TaskId = 10, TaskDesc  = "TaskDesc 0" },
    new { TaskId = 11, TaskDesc  = "TaskDesc 1" },
    new { TaskId = 12, TaskDesc  = "TaskDesc 2" }
};
var workgroup = new[] { //workgroup
    new { WorkGroupId = 100, WGDesc  = "WGDesc 0" },
    new { WorkGroupId = 101, WGDesc  = "WGDesc 1" },
    new { WorkGroupId = 102, WGDesc  = "WGDesc 2" }
};
var applicationuser = new[] { //applicationuser
    new { AUId = 1000, AUDesc  = "AUId 0" },
    new { AUId = 1001, AUDesc  = "AUId 1" }
};
    var results = from wb in workbasketitems 
        join wft in workflowtasks on wb.TaskId equals wft.TaskId
        join wg in workgroup on wb.WorkGroupId equals wg.WorkGroupId        
        select new { wft.TaskDesc, wg.WGDesc, wb.ActionUserId, wb.Work};
    results.Dump();

    var resultsInner = from wb in results 
        join au in applicationuser on wb.ActionUserId equals au.AUId into wbl
        from auList in wbl.DefaultIfEmpty()
        select new { wb.TaskDesc, wb.WGDesc, Desc = (auList == null? "BlAnk": auList.AUDesc), wb.Work};     
    resultsInner.Dump();

有沒有一種方法可以組合下面的Linq查詢，這對我保持可維護性很有幫助。 上面的代碼在Linqpad中工作，並且resultsInner是新創建的結果表的內部聯接。

Answer 1

你快到了。 只需將您在第二個查詢中執行的額外left join聯接添加到第一個查詢中：

var results = from wb in workbasketitems
              join wft in workflowtasks on wb.TaskId equals wft.TaskId
              join wg in workgroup on wb.WorkGroupId equals wg.WorkGroupId
              join au in applicationuser on wb.ActionUserId equals au.AUId into wbl
              from auList in wbl.DefaultIfEmpty()
              select new { wft.TaskDesc, wg.WGDesc, Desc = (auList == null ? "BlAnk" : auList.AUDesc), wb.Work };

---

您還可以使用DefaultIfEmpty的其他重載來指定在left join結果為null ：

var results = from wb in workbasketitems
              join wft in workflowtasks on wb.TaskId equals wft.TaskId
              join wg in workgroup on wb.WorkGroupId equals wg.WorkGroupId
              join au in applicationuser on wb.ActionUserId equals au.AUId into wbl
              from auList in wbl.DefaultIfEmpty(new { AUId = wb.ActionUserId, AUDesc = "Blank" } )
              select new { wft.TaskDesc, wg.WGDesc, Desc = auList.AUDesc, wb.Work };

Answer 2

您在尋找這個嗎？

var results = from wb in workbasketitems 
    join wft in workflowtasks on wb.TaskId equals wft.TaskId
    join wg in workgroup on wb.WorkGroupId equals wg.WorkGroupId
    join au in applicationuser on wb.ActionUserId equals au.AUId into wbl
    from auList in wbl.DefaultIfEmpty()
    select new { wft.TaskDesc, wg.WGDesc, Desc = (auList == null? "Blank": auList.AUDesc), wb.Work};

與可維護性沒有關系。 但是在這種情況下，您將省略其他投影。