how to map only if destination object doesn't have a value in Automapper

Question

I have a mapper in place and I need to perform a conditional mapping, Condition is, map the value from source to destination only if the destination property value is null. How would I do that?

.ForMember(o => o.EmployeeId, opt => opt.MapFrom(u => u.EmployeeId))

I want to assign value to EmployeeId only if it does't have a value already.

Thanks Lucian for response, I did go through this documentation before posting here, in documentation and all the other places I only found a way to put condition on source property not on destination property. — Gan3i
– Gan3i, Commented Nov 24, 2019 at 16:22
There are many Condition/PreCondition overloads. You just have to find the right one. — Lucian Bargaoanu
– Lucian Bargaoanu, Commented Nov 24, 2019 at 16:43
Yes and all those methods work only on source object property. I did find a way of writing it on destination object property. — Gan3i
– Gan3i, Commented Nov 24, 2019 at 17:19

Caleb Krise · Accepted Answer · 2022-12-12 20:05:31Z

2

The method of IMemberConfigurationExpression .MapFrom() has the overload that takes an IDestination void MapFrom<TResult>(Func<TSource, TDestination, TResult> mappingFunction); In your mapping function you can check the destination object.

Example:

.ForMember(dest => dest.EmployeeId, opt => opt.MapFrom((src, dest) => dest ?? src.EmployeeId))

edited Dec 12, 2022 at 20:05

answered Apr 27, 2020 at 21:42

Caleb Krise

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Allen Rufolo · Accepted Answer · 2024-11-15 16:02:44Z

0

Late answer but may help someone. This is what ended up working for me in ASP Net 6

//Only add email address if email is null or empty on the destination user object
CreateMap<UserProfile, User>()
            .ForMember(dest => dest.Email, opt => opt.PreCondition((src, dest, ctx) => string.IsNullOrEmpty(dest.Email)));

answered Nov 15, 2024 at 16:02

Allen Rufolo

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