Automapper - Don't map when a source object has a property with a value

Question

Our entities have a field called "DateDeleted". At times we might have these loaded into entities and we want to filter them out before sending them to the client.

Our Entities also have child entities which have child entities, all who have a DateDeleted.

What's the best practice to implement this with Automapper - Specifically - how can I map a Null value to the destination (for the entire object) when the source has a Date Deleted property with a value?

Robert Petz · Accepted Answer · 2017-06-09 18:38:05Z

3

You can ignore a specific property when you configure your mappings

CreateMap<srcType, destType>.ForMember(x => x.DateDeleted, opt => opt.Ignore());

EDIT: To do custom conditional logic during the mapping you will need to implement a custom resolver:

public class NullCheckResolver : IValueResolver<TSrc, TDest, TProp>
{
    public TProp Resolve(TSrc source, TDest destination, TProp member, ResolutionContext context)
    {
        if (member.DateDeleted == null)
            return member;
        return null;
    }
}

CreateMap<TSrc, TDest>().ForMember(dest => dest.MyOptionalProperty, opt => opt.ResolveUsing<NullCheckResolver>());

For more details on custom resolvers, see the AutoMapper documentation

edited Jun 9, 2017 at 18:38

answered Jun 8, 2017 at 21:22

Robert Petz

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8 Comments

Ryan Ternier Over a year ago

I don't want to ignore the property, I don't want to map the object if the objects property is a certain value

Robert Petz Over a year ago

I see what you are saying, give me a second I'll update my answer

David Libido Over a year ago

Why would you want to do this using automapper instead of filtering the result set before mapping?

Robert Petz Over a year ago

@DavidLibido 1. efficiency - if you filter the result set before hand then you loop over the collection once to filter the values and again to do the mapping, whereas with this route you only loop over the collection once. 2. configuration - if you have a lot of different places that need to perform this mapping (say between a Model and a ViewModel on a bunch of different controllers) then you can configure this in one location and it would apply to all places that perform that mapping. That being said, there is a time and a place for AutoMapper and it needs to be justified.

Robert Petz Over a year ago

@RyanTernier apologies - I had a typo. The resolver should return TProp in my example. TProp should be the object type of the property you want to conditionally return null on

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