使用linq进行分组，然后使用where条件运行select查询

Question

I have a class, OrderInfo shown below,

 class OrderInfo
 {
    string Product
    boolean NoIssues
 }

I have a list of OrderInfo. What I would like to do is to know for each product if there is an issue or not. So below is an example of my list.

 ProductList

 Product      NoIssues
 ABC          true
 ABC          true
 ABC          false
 ABC          true
 EFG          true
 EFG          true
 EFG          true
 EFG          true
 EFG          true

Below is the result I would like.

Result      
ABC       false
EFG       true

So I was going to use LINQ to group by product to get a unique list of products and then loop through this list to run a select query where I filter on NoIssues = false. However not sure how to do this or if this is the best way

 var res = (from ord in ProductList
            group ord by ord.Product).ToList()

So I believe the code above will give me a unique list of products that I can loop through. But not sure whats happens if I use a select statement with a where condition where nothing is returned?

Answer 1

You can use All :-

List<OrderInfo> result = list.GroupBy(x => x.Product)
                             .Select(x => new OrderInfo
                                       {
                                           Product = x.Key,
                                           NoIssues = x.All(z => z.NoIssues)
                                       }).ToList();

Or if you prefer query syntax:-

List<OrderInfo> result = (from ord in ProductList
                         group ord by ord.Product into g
                         select new OrderInfo
                               {
                                    Product = g.Key,
                                    NoIssues = g.All(x => x.NoIssues)
                               }).ToList();

Answer 2

If you don't want to create new Product objects for this, I would go with:

var result = from product in ProductList
             group product by product.Product into productGroup
             select productGroup.Where(p => !p.NoIssues)
                                .DefaultIfEmpty(productGroup.First())
                                .First();

Otherwise, @Rahul Singh's answer is more intuitive.