AutoMapper Writing Null On Target Field When Source Field Does Not Exist

Question

I have the following objects:

public class DomainStudent {
    public long Id { get; set; }
    public string AdvisorId { get; set; }
}

public class ApiStudent {
    public long Id { get; set; }
    public long AdvisorName { get; set; }
}

When I run the following mapping:

ApiStudent api = new ApiStudent();
api.Id = 123;
api.AdvisorName = "Homer Simpson";

DomainStudent existing = service.load(api.Id); // 123
// at this point existing.AdvisorId = 555

existing = Mapper.Map<ApiStudent, DomainStudent>(api);
// at this point existing.AdvisorId = null

How can I configure AutoMapper such that when the property AdvisorId is missing from the source object, so that it does not get overwritten to null?

Could you please correct the code first? AdvisorName is declared as long but "Homer Simpson" is assigned to it. — peflorencio
– peflorencio, Commented Apr 10, 2013 at 16:09
Does this question: Merge two objects to produce third using AutoMapper help you at all? — Ryan Gates
– Ryan Gates, Commented Apr 10, 2013 at 16:15
This isn't quite what I want. ... what I want is to NOT overwrite a field to NULL if it didn't have a matching field on the source object. — Adam Levitt
– Adam Levitt, Commented Apr 10, 2013 at 18:13

peflorencio · Accepted Answer · 2013-04-16 10:47:05Z

3

You must change the Map() call to:

Mapper.Map(api, existing);

and then configure the mapping to:

 Mapper.CreateMap<ApiStudent, DomainStudent>()
            .ForMember(dest => dest.AdvisorId, opt => opt.Ignore());

edited Apr 16, 2013 at 10:47

answered Apr 10, 2013 at 18:41

peflorencio

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2 Comments

Ryan Gates Over a year ago

The second code snippet should be Mapper.CreateMap<ApiStudent, DomainStudent>()... instead of CreateMap<ApiStudent, DomainStudent>()... since CreateMap is a static method.

peflorencio Over a year ago

@RyanGates Fixed. I copied from my AutoMapper Profile classes and forgot to change it.

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