带有布尔异步调用的 EF Core 3.1 客户端评估问题

Question

I am migrating form .Net 2.1 to 3.1 and this is including EF Core upgrade.

Now I had LINQ query as following, that worked with no issues:

var application = await _db.CustomerApplications
                .AsNoTracking()
                .Include(i => i.CustomerApplicationFields)
                .Include(i => i.Customer)
                .Where(x => x.Customer.PublicId == formId && x.IsPublished) // Also tried with &
                .OrderByDescending(o => o.Version)
                .FirstOrDefaultAsync();

With EF Core 3.1 I get error:

The LINQ expression 'DbSet<CustomerApplication>
    .Where(c => !(c.Deleted))
    .Join(
        outer: DbSet<Customer>
            .Where(c0 => !(c0.Deleted)), 
        inner: c => EF.Property<Nullable<long>>(c, "CustomerId"), 
        outerKeySelector: c0 => EF.Property<Nullable<long>>(c0, "Id"), 
        innerKeySelector: (o, i) => new TransparentIdentifier<CustomerApplication, Customer>(
            Outer = o, 
            Inner = i
        ))
    .Where(c => c.Inner.PublicId == __formId_0 && c.Outer.IsPublished)' 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(). See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.

When I convert this query as following, then it works (moving bool evaluation outside):

var application = await _db.CustomerApplications
                .AsNoTracking()
                .Include(i => i.CustomerApplicationFields)
                .Include(i => i.Customer)
                .Where(x => x.Customer.PublicId == formId)
                .OrderByDescending(o => o.Version)
                .ToListAsync();

var result = application.FirstOrDefault(x => x.IsPublished);

Could someone explain to me, why this is an issue? I also tried x.IsPublished == true , which had no effect. This seems to be quite random.

I also tried with AsTracking() .

Answer 1

Before EF Core 3.0, queries that could not be translated into SQL queries were evaluated on the client side. This behaviour was dismissed and an exception is thrown instead of evaluating non-translatable queries on the client side, now.

Also I think the new behaviour should not lead to any big performance issues when you write var result = application.FirstOrDefault(x => x.IsPublished); separately, because the same thing happened before. It was just not visible before. (Please correct me if this assumption is wrong!)

Also you can try following if you want to have one query (did not test this):

var application = await _db.CustomerApplications
            .AsNoTracking()
            .Include(i => i.CustomerApplicationFields)
            .Include(i => i.Customer)
            .Where(x => x.Customer.PublicId == formId)
            .OrderByDescending(o => o.Version)
            .FirstOrDefaultAsync(x => x.IsPublished);

You can read about it in detail here: https://docs.microsoft.com/en-us/ef/core/what-is-new/ef-core-3.0/breaking-changes#linq-queries-are-no-longer-evaluated-on-the-client

Answer 2

您应该使用 && 而不是 & 或者您可以添加另一个 where 子句。