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();

Is there a way to combine the below Linq queries, and is that helpful as I want keep things maintainable. The above works in Linqpad with resultsInner being an Inner Join of the newly created results table.

Answer 1

You are almost there. Just add the extra left join that you are performing in the second query to the first query:

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 };

---

You can also use the other overload of DefaultIfEmpty to specify what to do in a case when the left join results with a 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

Have you looking for this:

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};

Related to maintainablity there is no impact. But in this case you have ommited extra projections.