LINQ按可空子级和父级分组

Question

everyone! I've just faced a problem with timing out in my LINQ query. I have 3 tables: Work, Projects and Subprojects.

    Projects:
    +--------+
    |  Id    |<--+<--+
    |  Name  |   |   |
    +--------+   |   |
    SubProjects: |   |
    +--------+   |   |
 +->|  Id    |   |   |
 |  |  Name  |   |   |
 |  | ProjId |---+   |
 |  +--------+       |
 |  Work:            |
 |  +------------+   |
 |  |  Id        |   |
 |  |  Type      |   |
 |  |  ProjId    |---+
 +--|  SubProjId | (nullable)
    +------------+

I need to create a report based on Subprojects:

• Group by subproject Id,
• if subproject Id is null -> group by project Id

I've solved it by making two queries and then merging them, but when sometimes it times out. I was doing it with

result1.AddRange(result2);

because

var temp = result1.Concat(result2);

is throwing an Exception:

Internal .NET Framework Data Provider error 1004, 0, Unresolvable Var used in Command: VarType=Computed, Id=2090.

Can somebody help me with creating it in one query?

Answer 1

I'm not sure what your code looks like so this might not be perfect but you could try something like this:

var result = from work in works
             group work by work.SubProjId ?? work.ProjId into groupedWorks
             select groupedWorks.ToList();

or

var result = works.GroupBy(work => work.SubProjId ?? work.ProjId).ToList();

Answer 2

试试这个查询

var itemlist =contex.Work.where(x=>x.SubProjId !=null).Groupby(x=>x.SubProjId).Concat(Contex.Work.where(x=>x.SubProjId ==null).Groupby(x=>x.ProjId)).ToList();    

Answer 3

I'm guessing this is what you need:

var groups = from work in ctx.Works // the work table
             group work // we want to group whole work "rows"
                // we are grouping by project id and subproject id
                by new { ProjId = work.ProjId, SubProjId = work.SubProjId } 
                into g // and we are calling the grouping 'g'
             select g; // select the group

// example of doing something with the groupings
foreach (var group in groups)
{
   var key = group.Key; // gets a { ProjId, SubProjId } tuple
   foreach (var work in group)
   {
      // each work is a row in the Work-table
   }
}