efcore: The LINQ expression 'CompareString' could not be translated VB.NET

@maumar @roji Is there an easy way to add this translation from outside?

CompareString([i].ViewModel, __$VB$Local_viewModelName_0, False) == 0)

It should be possible to add a visitor at the end of preprocessing that identifies CompareString with (a) third parameter equal to False, and (b) compared to 0 - this seems like what the VB compiler emits for the VB equality operator (docs). This visitor would simply convert that to an equality node. I can knock it up tomorrow.

See #10707. Without Re-linq we will have to translate these explicitly.

Hi @ajcvickers thank you very much for your help.

Could you give me an example of how to introduce this translate CompareString in EFCore?. Please!! I have this reference, but in EF Core 3.1 I don’t find this class: Here

@estyfen all new development such as this is going into 5.0, except for critical bugs with no workarounds (which this probably won’t qualify for). However, we will be regular previews for 5.0 starting soon that you can test and work on, and as a workaround you can also add the visitor yourself as described above.

@estyfen yeah, can you please open a new issue for that?

I was thinking of <OptionCompare>, but it just changes the argument passed–there’s no way to remove the call entirely. <RemoveIntegerChecks> will remove the overflow checking…

Note from team discussion: when doing this in the product consider using name matching rather than relying on the exact type, since Rosyln emits some VB types into the VB assembly.

@bricelam I haven’t been able to find any info on having the compiler spit out C#-like IL. Any ideas where this is documented?

I’ve written a visitor that takes care of normalizing VB.NET string comparison, see #19681.

It’s possible to make this work right now, by copying that visitor and inserting it at the beginning of preprocessing in the query pipeline, something like the following:

public class VisualBasicRelationalQueryTranslationPreprocessorFactory : IQueryTranslationPreprocessorFactory
{
    private readonly QueryTranslationPreprocessorDependencies _dependencies;
    private readonly RelationalQueryTranslationPreprocessorDependencies _relationalDependencies;

    public VisualBasicRelationalQueryTranslationPreprocessorFactory(
        [NotNull] QueryTranslationPreprocessorDependencies dependencies,
        [NotNull] RelationalQueryTranslationPreprocessorDependencies relationalDependencies)
    {
        _dependencies = dependencies;
        _relationalDependencies = relationalDependencies;
    }

    public virtual QueryTranslationPreprocessor Create(QueryCompilationContext queryCompilationContext)
        => new VisualBasicRelationalQueryTranslationPreprocessor(_dependencies, _relationalDependencies, queryCompilationContext);
}

public class VisualBasicRelationalQueryTranslationPreprocessor : RelationalQueryTranslationPreprocessor
{
    public VisualBasicRelationalQueryTranslationPreprocessor(
        [NotNull] QueryTranslationPreprocessorDependencies dependencies,
        [NotNull] RelationalQueryTranslationPreprocessorDependencies relationalDependencies,
        [NotNull] QueryCompilationContext queryCompilationContext)
        : base(dependencies, relationalDependencies, queryCompilationContext)
    {
    }

    public override Expression Process([NotNull] Expression query)
    {
        query = new LanguageNormalizingExpressionVisitor().Visit(query);
        return base.Process(query);
    }
}

public class BlogContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(@"...");
        optionsBuilder.ReplaceService<IQueryTranslationPreprocessorFactory, VisualBasicRelationalQueryTranslationPreprocessorFactory>();
    }
}

Of course, that’s all C# 😃 Can @bricelam help us translate all that to VB.NET?