c# - 具有动态列组的 LINQ GroupBy

Question

我有一个这样的表:

 variety category  quantity
----------------------------------------------
  rg      pm         10
  gs      pm          5
  rg      com         8

我想根据这些 bool 参数创建一个 GroupBy:

• IncludeVariety
• IncludeCategory

例如:

IncludeVariety = true;
IncludeCategory = true;

会返回这个:

 variety category  quantity
----------------------------------------------
  rg      pm         10
  gs      pm          5
  rg      com         8

还有这个:

IncludeVariety = true;
IncludeCategory = false;

会返回这个:

  variety category  quantity
----------------------------------------------
    rg      -         18
    gs      -          5

还有这个:

IncludeVariety = false;
IncludeCategory = true;

会返回这个:

  variety category  quantity
----------------------------------------------
     -      pm         15
     -      com         8

你明白了......

问题:如何使用 LINQ 实现此目的？

重要:我已将问题简化为两个 bool 变量(IncludeVariety 和IncludeCategory)但在实际上我会有更多专栏(比如五个)

我不知道如何动态生成查询(.GroupBy 和 .Select):

 rows.GroupBy(r => new { r.Variety, r.Category })
 .Select(g => new 
  {
        Variety = g.Key.Variety,
        Category = g.Key.Category,
        Quantity = g.Sum(a => a.Quantity),
  });

 rows.GroupBy(r => new { r.Category })
 .Select(g => new 
  {
        Variety = new {},
        Category = g.Key.Category,
        Quantity = g.Sum(a => a.Quantity),
  });

 rows.GroupBy(r => new { r.Variety })
 .Select(g => new 
  {
        Variety = g.Key.Variety,
        Category = new {},
        Quantity = g.Sum(a => a.Quantity),
  });

我过去做过的类似事情是连接Where，例如:

  var query = ...

  if (foo) {
       query = query.Where(...)
  }

  if (bar) {
       query = query.Where(...)
  }

  var result = query.Select(...)

我可以在这里做类似的事情吗？

Answer 1

var results=items
  .Select(i=>
    new {
      variety=includevariety?t.variety:null,
      category=includecategory?t.category:null,
      ...
    })
  .GroupBy(g=>
    new { variety, category, ... }, g=>g.quantity)
  .Select(i=>new {
    variety=i.Key.variety,
    category=i.Key.category,
    ...
    quantity=i.Sum()
  });

缩短:

var results=items
  .GroupBy(g=>
    new {
      variety=includevariety?t.variety:null,
      category=includecategory?t.category:null,
      ... 
    }, g=>g.quantity)
  .Select(i=>new {
    variety=i.Key.variety,
    category=i.Key.category,
    ...
    quantity=i.Sum()
  });