EF Core 2 GroupBy Count predicate ignored

问题

I currently have the following code:

var result = query<Items>()
            .Where(x => x.Id == someId)
            .SelectMany(x => x.SubItems)
            .GroupBy(x => x.SubItemId)
            .Select(x => new ItemModel
            {   
                SubItemId = x.Key,
                SpecialItemCount = x.Where(y => y.IsSpecial == false).Count(),
            })
            .ToList()...

When I call "Count()" it queries all subitem count ignoring my predicate "y.IsSpecial". I tried that on EF Core 2.0.X and EF Core 2.1 preview 2, is that possibly a bug?

回答1:

You need to upgrade to EF Core 2.1 where GroupBy is supported : https://docs.microsoft.com/en-us/ef/core/what-is-new/ef-core-2.1

回答2:

Same problem here with EF Core 3.0. Seems to be bug in EF - you can workaround by using

SpecialItemCount = x.Sum(y => y.IsSpecial ? 0 : 1)

instead of

SpecialItemCount = x.Count(y => y.IsSpecial == false)

来源：https://stackoverflow.com/questions/50160399/ef-core-2-groupby-count-predicate-ignored