Linq内部联接复杂查询

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();

有没有一种方法可以组合下面的Linq查询，这对我保持可维护性很有帮助。 上面的代码在Linqpad中工作，并且resultsInner是新创建的结果表的内部联接。

Answer 1

你快到了。 只需将您在第二个查询中执行的额外left join联接添加到第一个查询中：

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 };

---

您还可以使用DefaultIfEmpty的其他重载来指定在left join结果为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

您在寻找这个吗？

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};

与可维护性没有关系。 但是在这种情况下，您将省略其他投影。