Automapper Expression 将一个属性映射到多个

Question

I'm running a WebAPI,

 Asp.Net Core 3.1 Automapper: 9.0 Automapper.Extensions.ExpressionMapping: 3.1

My LocaleDto PK is a composite key of 2 FK - LanguageCode and CountryCode

  public class LocaleDto 
    {
        [Key, ForeignKey(nameof(Language)), Column(Order = 0)]
        public string LanguageCode { get; set; }

        public LanguageDto Language { get; set; }

        [Key, ForeignKey(nameof(Country)), Column(Order = 1)]
        public string CountryCode { get; set; }

        public CountryDto Country { get; set; }
    }

I would like to map LocaleDto to LocaleViewModel, where Id is build based on the following pattern languageCode-CountryCode ie. en-GB

 public class LocaleViewModel 
    {
        public string Id {get;set;}
        public string LanguageCode { get; set; }
        public LanguageViewModel Language { get; set; }
        public string CountryCode { get; set; }
        public CountryViewModel Country { get; set; }
    }

The following mapping works just fine when I map one object to another using a static helper method:

  CreateMap<LocaleDto, LocaleViewModel>()
                    .ForMember(dest => dest.Id, opt => opt.MapFrom(src => LocalisationHelper.ToLocaleCode(src.LanguageCode, src.CountryCode)));

            CreateMap<LocaleViewModel, LocaleDto>()
                    .ForMember(dest => dest.LanguageCode, src => src.MapFrom(x => x.LanguageCode))
                    .ForMember(dest => dest.CountryCode, src => src.MapFrom(x => x.CountryCode));
...
  public static string ToLocaleCode(string languageCode, string countryCode)
        {
            if (!string.IsNullOrEmpty(languageCode) && !string.IsNullOrEmpty(countryCode))
            {
                return $"{languageCode}-{countryCode}";
            }
            return null;
        }

But when I map the expression, the result is not understandable in LINQ to SQL, cause it contains the helper LocalisationHelper.ToLocaleCode.

Expression<Func<LocaleViewModel, bool>> filter = x => x.Id == "en-GB";
var entityFilter = mapper.MapExpression<Expression<Func<LocaleDto, bool>>>(filter);

Inspect of entityFilter:

 {Param_0 => (ToLocaleCode(Param_0.LanguageCode, Param_0.CountryCode) == "en-GB")}

Exception

     The LINQ expression 'DbSet<LocaleDto>
         .Where(l => LocalisationHelper.ToLocaleCode(
             languageCode: l.LanguageCode, 
             countryCode: l.CountryCode) == "en-GB")' 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.

Is there a way to differently map those properties in Automapper so the result can be translated to SQL, without the need of switching to client evaluation?

Answer 1

What if you tried instead of using a static function evaluate the expression directly

CreateMap<LocaleDto, LocaleViewModel>()
   .ForMember(dest => dest.Id, opt => opt.MapFrom(src => src.LanguageCode + "-" + src.CountryCode));

Answer 2

The Where condition in your current linq is generated on the server , and your server does not define the LocalisationHelper.ToLocaleCode method, so this exception will occur.

To solve this problem, you only need to convert the DbSet<LocaleDto> to list or enumerable before the where condition(which has mentioned in the exception), so that the where condition can be guaranteed to run under the client condition .

Change your code as follow:

DbSet<LocaleDto>.ToList().Where(l => LocalisationHelper.ToLocaleCode(l.LanguageCode,l.CountryCode) == "en-GB")

Update

Here is the second method:

Func<LocaleDto, bool> IsMatch = (x) =>
            ((!string.IsNullOrEmpty(x.LanguageCode) && !string.IsNullOrEmpty(x.CountryCode))
            ? $"{x.LanguageCode}-{x.CountryCode}" : null) == "en-GB";

var query = DbSet<LocaleDto>.Where(IsMatch).ToList();

You can also refer to this .