在linq中分组后选择对象类型列表

Question

I have a table such as the following:

ProductId, CategoryId
123, Category1
123, Category2
123, Category1

My parameter is productId and I need to return a list of type Category based on distinct categories for the given productId in the above table.

Answer 1

You could leverage the .Distinct() function from LINQ to select all the distinct categories belonging to the specified productId.

var pList = (from p in context.Products 
where p.ProductId == productId 
select p.Category).Distinct().ToList();

Answer 2

var list = context.Products
  .Where(p=>p.ProductId==productId)
  .Distinct();