“LINQ 表达式‘DbSet’...”-EF Core + AutoMapper

Question

当我尝试通过 AutoMapper 将数据转换为另一种类型时，我得到以下函数：

System.InvalidOperationException: The LINQ expression 'DbSet<UserMaterial>()

System.InvalidOperationException
The LINQ expression 'DbSet<UserMaterial>()
    .Where(cm => cm.UserId == u.Outer.Outer.UserId)
    .Where(cm => DbSet<CourseMaterial>()
        .Where(courseMaterial => courseMaterial.CourseId == u.Outer.Outer.CourseId)
        .Select(courseMaterial => courseMaterial.MaterialId)
        .Any(materialId => materialId == cm.MaterialId)

)

    .Select(um => um.Grade)
    .OrderByDescending(grade => grade)
    .LastOrDefault(0)' 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 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.

代码（IPractiflyContext为接口（原类型为PractiflyContext(DbContext））：

public class PractiFlyProfile : Profile
{
    private readonly PractiFlyContext _context;

    public PractiFlyProfile(IPractiflyContext context)
    {
        _context = context;

        CreateProjection<UserCourse, UserCourseStatusDto>()
            .ForMember(e => e.CourseId, par => par.MapFrom(e => e.CourseId))
            .ForMember(e => e.Language, par => par.MapFrom(e => e.Course.Language.Code))
            // TODO: можливо оцінки беруться із тем та з матеріалів
            .ForMember(
                e => e.GradeAverage,
                par => par.MapFrom(
                    e => (
                        (float)_context
                            .Set<UserMaterial>()
                            .Where(cm => cm.UserId == e.UserId)
                            .Where(cm => _context.Set<CourseMaterial>()
                                .Where(courseMaterial => courseMaterial.CourseId == e.CourseId)
                                .Select(courseMaterial => courseMaterial.MaterialId)
                                .Any(materialId => materialId == cm.MaterialId))
                            .Select(um => um.Grade)
                            .DefaultIfEmpty()
                            .Average()
                        )
                    )
                )
            .ForMember(
                e => e.Grade,
                par => par.MapFrom(
                    e => _context
                        .UserMaterials
                        .Where(cm => cm.UserId == e.UserId)
                        .Where(cm => _context.CourseMaterials
                            .Where(courseMaterial => courseMaterial.CourseId == e.CourseId)
                            .Select(courseMaterial => courseMaterial.MaterialId)
                            .Any(materialId => materialId == cm.MaterialId)
                        )
                        .Select(um => um.Grade)
                        .OrderByDescending(grade => grade)
                        .LastOrDefault(0)
                )
            )
            .ForMember(
                e => e.Description,
                par => par.MapFrom(e => e.Course.Description)
            )
            .ForMember(
                e => e.Name,
                e => e.MapFrom(e => e.Course.Name)
            )
            .ForMember(
                e => e.Language,
                e => e.MapFrom(e => e.Course.Language.Code)
            )
            .ForMember(
                e => e.CourseId,
                e => e.MapFrom(e => e.CourseId)
            );
    }
}

我想尝试转换为另一种数据类型，但我一直出错。我认为原因在于上下文