c# - 将 VB Linq 转换为 C#

Question

我正在通过转换现有项目自学 C#，但在转换以下 vb linq 代码时遇到困难:

Dim outStuff = From tt In (From t In Products.SelectMany(Function(p) If(p.tags IsNot Nothing, p.tags, New ObservableCollection(Of TagModel)))
               Group By tagName = t.name,
                                  v = (Aggregate p In Products Where If(p.tags IsNot Nothing, p.tags.Contains(t), Nothing) Into Sum(p.views)),
                                  nl = (Aggregate p In Products Where If(p.tags IsNot Nothing, p.tags.Contains(t), Nothing) Into Sum(p.num_likes))
               Into g = Group, Count())
               Group By name = tt.tagName Into Count = Sum(tt.Count), viewsTotal = Sum(tt.v), num_likesTotal = Sum(tt.nl)
               Select name, Count, viewsTotal, num_likesTotal

其中 Products 作为 ObservableCollection(Of ProductModel)

到目前为止，我已经设法转换了这么多:

var x =  Products.SelectMany(p => (p.tags != null) ? p.tags : new ObservableCollection<TagModel>());
var tags = from t in x group t by t.name into g select new { tagname=g.First().name};

'Group By's 让我难住了。任何帮助都会很棒...

Answer 1

您的查询有点复杂且难以理解，但让我试着描述一下我认为您正在寻找的内容。你有一个产品列表，每个产品可能有一个或多个标签；你想要一个所有标签的列表，包括有多少产品有这个标签，有这个标签的产品的总浏览次数，以及有这个标签的产品的“喜欢”总数。如果是这种情况，以下应该可以解决问题:

// may want to add ToArray() here so that filter is not executed multiple times during subsequent query
var productsWithTags = Products.Where(p => p.tags != null);
var outStuff = from t in (from p in productsWithTags
               from t in p.tags
               select t).Distinct()
               let matchingProducts = productsWithTags.Where(p => p.tags.Contains(t))
               select new { name = t.name,
                            Count = matchingProducts.Count(),
                            viewsTotal = matchingProducts.Sum(p => p.views),  
                            num_likesTotal = matchingProducts.Sum(p => p.num_likes)
                          };