Mason Mason - 3 years ago 101
C# Question

How to ignore property of property in AutoMapper mapping?

Image a

Person
and a
Group
class with a many-to-many relationship. A person has a list of groups and a group has a list of people.

When mapping
Person
to
PersonDTO
I have a
stack overflow exception
because AutoMapper can't handle the
Person
>
Groups
>
Members
>
Groups
>
Members
>...

So here's the example code:

public class Person
{
public string Name { get; set; }
public List<Group> Groups { get; set; }
}

public class Group
{
public string Name { get; set; }
public List<Person> Members { get; set; }
}

public class PersonDTO
{
public string Name { get; set; }
public List<GroupDTO> Groups { get; set; }
}

public class GroupDTO
{
public string Name { get; set; }
public List<PersonDTO> Members { get; set; }
}


When I use .ForMember in creating a mapper, the first mapper that gets executed throws a
null reference exception
.

Here's the code for the mapper:

CreateMap<Person, PersonDTO>()
.ForMember(x => x.Groups.Select(y => y.Members), opt => opt.Ignore())
.ReverseMap();

CreateMap<Group, GroupDTO>()
.ForMember(x => x.Members.Select(y => y.Groups), opt => opt.Ignore())
.ReverseMap();


So what am I missing or doing wrong? When I remove the .ForMember methods, the
null reference exception
is not thrown anymore.

UPDATE: I really want to emphasize the main point of my question is how to ignore a property of a property. This code is just a rather simple example.

UPDATE 2: This is how I fixed it, big thanks to Lucian-Bargaoanu

CreateMap<Person, PersonDTO>()
.ForMember(x => x.Groups.Select(y => y.Members), opt => opt.Ignore())
.PreserveReferences() // This is the solution!
.ReverseMap();

CreateMap<Group, GroupDTO>()
.ForMember(x => x.Members.Select(y => y.Groups), opt => opt.Ignore())
.PreserveReferences() // This is the solution!
.ReverseMap();


Thanks to
.PreserveReferences()
the circular references get fixed!

Answer Source
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