Mapping:
.ForMember(dest => dest.DisplayName, opt => { opt.PreCondition(location => location.Parent != null); opt.MapFrom(src => src.Name + ", " + src.Parent.Name); }) .ForMember(dest => dest.DisplayName, opt => { opt.PreCondition((src, dest, context) => dest.DisplayName == null); opt.MapFrom(src => src.Name); }) Expected result:
If the first condition is met don't override the mapping.
What actually happens:
The second mapping is overriding the first mapping.
How can I solve this?
It doesn't work because you are overwriting previous mapping expressions calling another ForMember() for the same member, which is your case is DisplayName. Consider such case:
.ForMember(d => d.DisplayName, o => o.MapFrom(s => "1")) .ForMember(d => d.DisplayName, o => o.MapFrom(s => "2")) .ForMember(d => d.DisplayName, o => o.MapFrom(s => "3")); Which value will be mapped to DisplayName?
3
So in your case, your first conditional mapping expression is overwriten by the second one. To make it work, join the conditional mapping into one mapping expression:
.ForMember( dest => dest.DisplayName, opts => opts.MapFrom((src, dest) => { if (src.Parent != null) { return string.Join(", ", src.Name, src.Parent.Name); } else { if (dest.DisplayName is null) { return src.Name; } else { return "Some other value when no conditions were met."; } } })); 
if (dest.DisplayName is null). Also, you didn't mention you were looking for solutions "out of the box" in stated question. The core answer is still valid - you can't stack ForMember() methods for the same member.
It would be a cool feature to have but I don't see it anywhere in Automapper documentation.
This should however work in your case if the logic is not more complex.
.ForMember(dest => dest.DisplayName, opt => { opt.MapFrom(src => src.Name + (location.Parent != null ? ", " + src.Parent.Name : null)); }) 