Automapper - does not recognize string.format method

Question

I met today with strange behavior of AutoMapper library. Why string.Format in the second case does not work? Are you able to explain to me why the first case works when the second throwing an exception?

Mapping configuration: (working)

config.CreateMap<Person, PersonView>().
    ForMember(dest => dest.FullName, opt => opt.
       MapFrom(src => src.Data.Code + " - " + src.Number));

Mapping configuration: (not working)

config.CreateMap<Person, PersonView>().
    ForMember(dest => dest.FullName, opt => opt.
        MapFrom(src => string.Format("{0} - {1}", src.Data.Code, src.Number)));

Projection:

using (var ctx = new MyDbContext())
{
    return ctx.Persons.Include(i => i.Data).Project().To<PersonView>().ToList();
}

Exception:

Possible duplicate of LINQ to Entities does not recognize the method 'System.String ToString()' method in MVC 4 — Andrew Savinykh
– Andrew Savinykh, Commented Oct 15, 2015 at 20:07
SO is literally full of questions like this one. Did you search? One Two Three Four — Andrew Savinykh
– Andrew Savinykh, Commented Oct 15, 2015 at 20:08
And Charles is right it does not appear to have anything to do with Automapper. — Andrew Savinykh
– Andrew Savinykh, Commented Oct 15, 2015 at 20:09

Charles Mager · Accepted Answer · 2015-10-15 14:11:18Z

4

It's not really anything to do with AutoMapper.

You're effectively asking Entity Framework to translate an expression that calls a method (string.Format in this case) into SQL. It can't do that.

The first works because it's a simple string concatenation, which is more readily translated.

answered Oct 15, 2015 at 14:11

Charles Mager

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