I have an ASP .Net core application. I am simply trying to have my AutoMapper configure to convert a string comma delimited into a list of strings as per this configuration:
configuration.CreateMap<Job, JobDto>()
.ForMember(dto => dto.Keywords, options => options.MapFrom(entity => entity.Keywords.Split(',').ToList()))
For some reason it does not get compiled and give me the following error:
An expression tree may not contain a call or invocation that uses optional argument
I can't see why I am getting this error. I am pretty sure that I have done that in my other projects before without any such error.
This is completely true.
Error is raised because expression tree being created is about to contain some more complex logic, like .Split(',').ToList(), which is not an accessible property or method, only top-level reflected object properties and methods are supported (like in class MemberInfo).
Property chaining, deep-calls (.obj1property.obj2property), extension methods are not supported by the expression trees, like in this .ToList() call.
My solution was like this:
// Execute a custom function to the source and/or destination types after member mapping
configuration.CreateMap<Job, JobDto>()
.AfterMap((dto,jobDto)=>jobDto.Keywords = dto.Keywords.Split(',').ToList());