LINQ 表达式无法翻译

Question

I have the following database query where I am trying to check if there exists an item with a particular barcode that is linked to a particular mailbag. The query is as follows:

var exists = await dbcontext.Items
                .Include(t => t.MailBagItems)
                .ThenInclude(mt => mt.MailBag)
                .AnyAsync(t => t.Barcode.Equals(barcode) &&
                t.MailBagItems.FirstOrDefault() != null && 
t.MailBagItems.FirstOrDefault().MailBag.Number.ToLower().Equals(mailbagNumber.ToLower()));

For some reason, I'm getting the following exception:

System.InvalidOperationException: The LINQ expression could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync().

I know for a fact from removing parts of the boolean expression that the issue is in the last boolean condition where I'm checking the mailbag number. However, I get the same error if I remove the calls to ToLower(). Can someone indicate what is wrong with my expression and how to fix it? Please note I'm using .NET core 3 and SQL Server.

Answer 1

Managed to make the query work by changing it to the following:

var exists = dbcontext.Items
                .AnyAsync(t => t.Barcode.Equals(barcode) &&
                            t.MailBagItems.Any(t => t.MailBag.Number.ToLower().Equals(mailbagNumber.ToLower())));

Seems it wasn't enjoying the.FirstOrDefault().MailBag before.

Answer 2

Your AnyAsync is to complex for EF to transform to SQL, if you want to still use that query you will have to materialize the entities first, like this:

var exists = dbcontext.Items
                .Include(t => t.MailBagItems)
                .ThenInclude(mt => mt.MailBag)
                .ToListAsync()
                .AnyAsync(t => t.Barcode.Equals(barcode) &&
                t.MailBagItems.FirstOrDefault() != null && 
t.MailBagItems.FirstOrDefault().MailBag.Number.ToLower().Equals(mailbagNumber.ToLower()));

Also you are missing the await keyword, or was that intended?