LINQ Group By to project into a non-anonymous type?

问题

I have the following LINQ example:

var colorDistribution = 
    from product in ctx.Products
    group product by product.Color
    into productColors

    select
       new 
    {
       Color = productColors.Key,
       Count = productColors.Count()
    };

All this works and makes perfect sense.

What I'm trying to achieve is to group by into a strong type instead of anonymous type.

For example I have a ProductColour class and I would like to Group into a List<ProductColour>

Is this possible?

Thank you

回答1:

EDIT: Okay, I'd completely misread your post. By the looks of it, you're not wanting to group by a different type - you're wanting to project each element of the group into a different type. Here's what I'd do:

var colorDistributionSql = 
    from product in ctx.Products
    group product by product.Color
    into productColors

    select
       new 
    {
       Color = productColors.Key,
       Count = productColors.Count()
    };

var colorDistributionList = colorDistributionSql
      .AsEnumerable()
      .Select(x => new ProductColour(x.Color, x.Count))
      .ToList();

回答2:

LinqToSql does allow direct projection of the group into a type (after all, the group is just an IGrouping<T, U>, a type). What LinqToSql can't do, is translate a constructor into SQL.

IQueryable<ProductColour> colorDistributionSql =  
    from product in ctx.Products 
    group product by product.Color 
    into productColors 
    select new ProductColour()
    { 
       Color = productColors.Key, 
       Count = productColors.Count() 
    };

来源：https://stackoverflow.com/questions/2927618/linq-group-by-to-project-into-a-non-anonymous-type

标签

sql

linq

group-by

anonymous-types