IQueryable ProjectTo + other ideas

[CaptTwigg]

Hello, thank you for a great tool!
I'm in the process of replacing AutoMapper with Mapperly, and in that process I have some ideas to new features, that you maybe already have thought about, but anyway.

Not sure if you would like a new discussion for every idea, so I will start with one here.
Generate a "ProjectTo" IQueryable like AutoMapper Queryable-Extensions and preferable with some recursion with a limit [RecursionDepth(<some number>)]?

[ziaulhasanhamim]

ProjectTo is very essential for ef core mappings. Also there can be a method like GetMappingExpression which will return an expression which can be passed into Select method of ef core or even mongodb.

[Thundarr1974]

Hello. Just wanted to pass along a library I found to accomplish using Mapperly functions in LINQ expressions (for DSL translations like SQL, COSMOS, etc.)

https://github.com/hazzik/DelegateDecompiler

It allows for decompiling the generated function into expression trees. Here's a sample for how we're using it:

[Mapper]
public partial class ModelViewMapper
{
    public ModelViewMapper()
    {
        CustomerViewProjection = GetProjection((Func<Customer, CustomerView>)CustomerToCustomerView);
    }

    [MapProperty($"{nameof(Customer.CustomerSubscription)}.{nameof(Customer.CustomerSubscription.Subscription)}.{nameof(Customer.CustomerSubscription.Subscription.Name)}", nameof(CustomerView.Subscription))]
    public partial CustomerView CustomerToCustomerView(Customer customer);

    public Expression<Func<Customer, CustomerView>> CustomerViewProjection { get; }

    private static Expression<Func<TIn, TOut>> GetProjection<TIn, TOut>(Func<TIn, TOut> func) => (Expression<Func<TIn, TOut>>)func.Decompile();
}
....

        var db = ServiceProvider.GetRequiredService<SomeDbContext>();
        var mapper = ServiceProvider.GetRequiredService<ModelViewMapper>();

        return await db.Customers
            .AsNoTracking()
            .Include(c => c.CustomerSubscription.Subscription)
            .Select(mapper.CustomerViewProjection)
            .GetPaged(request, c => c.Id, cancellationToken);

[latonz]

@CaptTwigg ProjectTo should now be supported in 2.8.0-next.1 (see next docs) and #214. Any feedback is welcome 😊 Note that these API's are still in an early preview and could break again until 2.8.0 is released.
Closing for now, as the main issue should be resolved. Feel free to open a new discussion for further improvements (eg. regarding the recursion limit).

A recursion limit is not yet supported, could you add a sample for your use case including how the configuration and the generated code could look like?

[KuraiAndras]

Hey, @latonz I just checked out the 2.8.0-next.1 and the documentation states, that user implemented mappings are not supported. Are there any plans for supporting those?

[Yutsa]

Okay I'm very sorry, forget everything I've said. The mapping method was incomplete and graphql was requesting a field that wasn't mapped. It does work correctly if I request the right fields !

I'm glad that it works and sorry for the inconvenience.

I have the following mapper :

[Mapper]
public static partial class WorkHeaderDtoMapperly
{

    public static WorkHeaderDto WorkToWorkHeaderDto(this WorkHeader workHeader)
    {
        var dto = workHeader.MapInternal();
        dto.StartDate = workHeader.Works.Min(w => w.StartDate);
        dto.EndDate = workHeader.Works.Min(w => w.EndDate);
        dto.Parcelles = workHeader.Works.SelectMany(w => w.Parcelles).Distinct();
        // dto.Tools = workHeader.Works.SelectMany(w => w.Tools).Select(t => t.Tool).Distinct();
        dto.Persons = workHeader.Works.SelectMany(w => w.Persons).Select(w => w.Person).Distinct();
        dto.TypeTravail = workHeader.Works.First().CategorieTravail.TypeTravail.TypeTravailId;
        dto.Travail = workHeader.Works.First().CategorieTravail.CategorieTravailId;
        dto.CategoryId = workHeader.Works.First().CategorieTravail.Category?.Id;
        dto.WorkArea = workHeader.Works.Sum(w => w.Quantity) ?? 0;
        return dto;
    }
    
    public static partial IQueryable<WorkHeaderDto> ProjectToDto(this IQueryable<WorkHeader> workHeader);
    
    private static partial WorkHeaderDto MapInternal(this WorkHeader workHeader);
}

And now I only need a way to reuse the custom mappings inside the IQueryable mapping method.

[latonz]

How does the generated code look like and how do you expect it to look like?

[Yutsa]

Basically I have some custom mapping logic that you can see inside my WorkToWorkHeaderDto. I managed to make it work in "classic" mapping using Before/After.

However I need the same mapping done for the IQueryable. Unfortunately I haven't found a way to make it work.

The best I've came up with is this :

    public static IQueryable<WorkHeaderDto> ProjectToDtoCustom(this IQueryable<WorkHeader> workHeader)
    {
        if (workHeader == null)
            return default;
        return workHeader.Select(workHeader => new WorkHeaderDto
        {
            StartDate = workHeader.Works.Min(w => w.StartDate),
            EndDate = workHeader.Works.Min(w => w.EndDate),
            Parcelles = workHeader.Works.SelectMany(w => w.Parcelles).Distinct(),
            Persons = workHeader.Works.SelectMany(w => w.Persons).Select(w => w.Person).Distinct(),
            TypeTravail = workHeader.Works.First().CategorieTravail.TypeTravail.TypeTravailId,
            Travail = workHeader.Works.First().CategorieTravail.CategorieTravailId,
            CategoryId = workHeader.Works.First().CategorieTravail.Category.Id,
            WorkArea = workHeader.Works.Sum(w => w.Quantity) ?? 0,
        });
    }

But it lacks the mapping done inside the generated MapInternal. I'm not an expert on Expression and its limitations. I tried calling the WorkToWorkHeaderDto method inside the Select but it selects all fields if I do that because it doesn't convert to an Expression by LINQ I guess.

[Yutsa]

By the way here was the generated code I I tried generating the IQueryable method

// <auto-generated />
#nullable enable
namespace ApiIdViniteca.Dto.Mappers
{
    public static partial class WorkHeaderDtoMapperly
    {
        public static partial global::System.Linq.IQueryable<global::ApiIdViniteca.Dto.WorkHeaderDto>? ProjectToDto(this global::System.Linq.IQueryable<global::Viniteca.Core.Metier.WorkHeader>? workHeader)
        {
            if (workHeader == null)
                return default;
#nullable disable
            return System.Linq.Queryable.Select(workHeader, x => x == null ? default : new global::ApiIdViniteca.Dto.WorkHeaderDto()
            {
                Id = x.Id,
                EntityCode = x.EntityCode,
                Comment = x.Comment,
                ModifiedBy = x.ModifiedBy,
            });
#nullable enable
        }

        private static partial global::ApiIdViniteca.Dto.WorkHeaderDto? MapInternal(this global::Viniteca.Core.Metier.WorkHeader? workHeader)
        {
            if (workHeader == null)
                return default;
            var target = new global::ApiIdViniteca.Dto.WorkHeaderDto();
            target.Id = workHeader.Id;
            target.EntityCode = workHeader.EntityCode;
            target.Comment = workHeader.Comment;
            target.ModifiedBy = workHeader.ModifiedBy;
            return target;
        }
    }
}

The IQueryable method doesn't call the basic one

[latonz]

The basic one is not called because the nullable types differ... Does it work if you remove the nullable annotations on the MapInternal types?