ProjectToType: Error while compiling when using extension methods.

[fretje]

When I update to the latest version that just came out, we get an "Error while compiling" when using ProjectToType:

Mapster.CompileException: Error while compiling
source=CloudConnector.Api.Domain.CommandRuns.CommandRun
destination=CloudConnector.Api.Application.CommandRuns.CommandRunDto
type=Projection
 ---> System.ArgumentNullException: Value cannot be null. (Parameter 'key')
   at System.Collections.Generic.Dictionary`2.FindValue(TKey key)
   at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
   at Mapster.Adapters.BaseClassAdapter.CreateClassConverter(Expression source, ClassModel classModel, CompileArgument arg, Expression destination, Boolean ctorMapping, ClassModel recordRestorMemberModel)
   at Mapster.Adapters.ClassAdapter.CreateInlineExpression(Expression source, CompileArgument arg, Boolean IsRequiredOnly)
   at Mapster.Adapters.BaseAdapter.CreateInlineExpressionBody(Expression source, CompileArgument arg)
   at Mapster.Adapters.BaseAdapter.CreateExpressionBody(Expression source, Expression destination, CompileArgument arg)
   at Mapster.Adapters.BaseAdapter.CreateAdaptFunc(CompileArgument arg)
   at Mapster.TypeAdapterConfig.CreateMapExpression(CompileArgument arg)
   --- End of inner exception stack trace ---
   at Mapster.TypeAdapterConfig.CreateMapExpression(CompileArgument arg)
   at Mapster.TypeAdapterConfig.CreateMapExpression(TypeTuple tuple, MapType mapType)
   at Mapster.TypeAdapterConfig.CreateProjectionCallExpression(TypeTuple tuple)
   at Mapster.TypeAdapterConfig.<>c__DisplayClass60_0`1.<AddToHash>b__0(TypeTuple types)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at Mapster.TypeAdapterConfig.AddToHash[T](ConcurrentDictionary`2 hash, TypeTuple key, Func`2 func)
   at Mapster.TypeAdapterConfig.GetProjectionCallExpression(Type sourceType, Type destinationType)
   at Mapster.Extensions.ProjectToType[TDestination](IQueryable source, TypeAdapterConfig config)
   ...

This is the mapperconfiguration. It does use extension methods... that might be the culprit.

public class MapperConfiguration : IMapperConfiguration
{
    public void Configure() =>
        TypeAdapterConfig<CommandRun, CommandRunDto>.NewConfig()
            .Map(
                dest => dest.CommandShortName,
                src => src.GetCommandShortName())
            .Map(
                dest => dest.CommandParameterDescription,
                src => src.GetCommandParameterDescription());
}

And indeed, when I re-write the expressions so they don't use extension methods, it works again:

        TypeAdapterConfig<CommandRun, CommandRunDto>.NewConfig()
            .Map(
                dest => dest.CommandShortName,
                src => CommandTypes.ShortNameFor(src.CommandType))
             .Map(
                dest => dest.CommandParameterDescription,
                src => ((ICommand)RequestFactory.Create(src.CommandType, src.CommandJson)).GetParameterDescription();

So there is a workaround...
But this is a regression, I'd say...

[DocSvartz]

Hi @fretje , this should be fixed in https://www.nuget.org/packages/Mapster/10.0.3

Thanks

update :
and https://www.nuget.org/packages/Mapster.EFCore/10.0.2

[frankyjquintero]

@DocSvartz
First of all, thank you for the latest release and the continuous improvements to Mapster.

Mapster ProjectToType fails with Mapping is invalid for projection

Description

When using ProjectToType<TResult>() over an IQueryable (EF Core), Mapster throws a CompileException indicating that the mapping is not valid for projection.

This occurs even when the mapping appears straightforward and no obvious custom logic is involved.

---

Exception

Mapster.CompileException: Error while compiling
source=WebApi.Example.Domain.Entities.Catalogos.Lugar
destination=WebApi.Example.Controllers.LugarDto
type=Projection
 ---> System.InvalidOperationException: Mapping is invalid for projection
   at Mapster.Adapters.BaseAdapter.CreateBlockExpressionBody(Expression source, Expression destination, CompileArgument arg)
   at Mapster.Adapters.BaseAdapter.CreateExpressionBody(Expression source, Expression destination, CompileArgument arg)
   at Mapster.Adapters.BaseAdapter.CreateAdaptFunc(CompileArgument arg)
   at Mapster.TypeAdapterConfig.CreateMapExpression(CompileArgument arg)
   --- End of inner exception stack trace ---
   at Mapster.TypeAdapterConfig.CreateMapExpression(CompileArgument arg)
   at Mapster.TypeAdapterConfig.CreateMapExpression(TypeTuple tuple, MapType mapType)
   at Mapster.TypeAdapterConfig.CreateProjectionCallExpression(TypeTuple tuple)
   at Mapster.TypeAdapterConfig.<>c__DisplayClass60_0`1.<AddToHash>b__0(TypeTuple types)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at Mapster.TypeAdapterConfig.AddToHash[T](ConcurrentDictionary`2 hash, TypeTuple key, Func`2 func)
   at Mapster.TypeAdapterConfig.GetProjectionCallExpression(Type sourceType, Type destinationType)
   at Mapster.Extensions.ProjectToType[TDestination](IQueryable source, TypeAdapterConfig config)
   at Infrastructure.Persistence.Repositories.ApplicationRepositoryBase`1.ApplySpecification[TResult](ISpecification`2 specification)

Code Context

    public class ApplicationRepositoryBase<T>(DbContext dbContext, ICacheService cache) : RepositoryBase<T>(dbContext), IAppRepositoryBase<T> where T : class, IBaseEntity
    {
        private readonly DbContext _dbContext = dbContext;
protected override IQueryable<TResult> ApplySpecification<TResult>(ISpecification<T, TResult> specification)
{
    if (specification.Selector is not null)
    {
        return base.ApplySpecification(specification);
    }

    var query = ApplySpecification(specification, false);
    return query.ProjectToType<TResult>();
}
......
}

Expected Behavior

ProjectToType() should generate a valid expression tree that can be translated by EF Core into SQL, as long as the mapping only involves simple property projections.

Actual Behavior

Mapster fails during expression compilation with:

Mapping is invalid for projection

There is no clear indication of which member or mapping rule is causing the issue.

Additional Context
Using Ardalis.Specification with EF Core
Projection is applied only when specification.Selector is null
The same mapping works correctly when executed in-memory using .Adapt()
Questions
Is there a way to get more detailed diagnostics about which part of the mapping is not translatable?
Are there known limitations or guidelines for using ProjectToType with EF Core?

using

We also tested EFCoreProjectToType, but encountered the same projection error.

[DocSvartz]

Hi @frankyjquintero it is work in 7.4.0?

[frankyjquintero]

@DocSvartz yes

[DocSvartz]

What specific types of TResult return error ? Record, class, or other

[frankyjquintero]

@DocSvartz
7.4.0

public class GetAllLocationSpecification : Specification<Lugar, LugarDto>
{
    public GetAllLocationSpecification(TipoLugar tipoLugar, string? lugarPadreID, bool esJurisdiccion = true)
    {
        if (lugarPadreID is not null)
        {
            Query.Where(p => p.TipoLugar == tipoLugar && p.IDLugarPadre == lugarPadreID);
        }
        else
        {
            if (tipoLugar == TipoLugar.Departamento)
                Query.Where(p => p.IDLugarPadre == "COL" && p.TipoLugar == tipoLugar);
            else
                Query.Where(p => p.TipoLugar == tipoLugar);
        }


        if (esJurisdiccion)
        {
            Query.Where(p => p.EsJurisdiccion);
        }
    }
}

TResult

public record LugarDto
{
    public string IDLugar { get; set; } = string.Empty;
    public string? IDLugarPadre { get; set; }
    public string Nombre { get; set; } = string.Empty;
}

[DocSvartz]

@frankyjquintero, Ok This seems to be related to the new handling of record types.
I'll move this to a separate issue.

[frankyjquintero]

@DocSvartz indeed, using class with version 10 works correctly. The issue is effectively caused when using record types.

public class LugarDto
{
    public string IDLugar { get; set; } = string.Empty;
    public string? IDLugarPadre { get; set; }
    public string Nombre { get; set; } = string.Empty;
}