Skip null values with custom resolver

Question

I want to use automapper to map between my public data contracts and my DB models. I have created a class which automatically goes through all the contracts are creates mappings. The only problem I have is that I only want to map values from the contract to the DB model if the value is not null. I have looked at other question on here but cant see examples that use custom resolvers.

Here is some of my code

var mapToTarget = AutoMapper.Mapper.CreateMap(contract, mappedTo);
foreach (var property in contract.GetProperties().Where(property => property.CustomAttributes.Any(a => a.AttributeType == typeof(MapsToProperty))))
{
  var attribute = property.GetCustomAttributes(typeof(MapsToProperty), true).FirstOrDefault() as MapsToProperty;

  if (attribute == null) continue;

  mapToTarget.ForMember(attribute.MappedToName,
                    opt => 
                        opt.ResolveUsing<ContractToSourceResolver>()
                            .ConstructedBy(() => new ContractToSourceResolver(new MapsToProperty(property.Name, attribute.SourceToContractMethod, attribute.ContractToSourceMethod))));
}


private class ContractToSourceResolver : ValueResolver<IDataContract, object>
{
  private MapsToProperty Property { get; set; }

  public ContractToSourceResolver(MapsToProperty property)
  {
     Property = property;
  }

  protected override object ResolveCore(IDataContract contract)
  {
     object result = null;
     if (Property.ContractToSourceMethod != null)
     {
         var method = contract.GetType()
                    .GetMethod(Property.ContractToSourceMethod, BindingFlags.Public | BindingFlags.Static);
          result = method != null ? method.Invoke(null, new object[] {contract}) : null;
      }
      else
      {
         var property =
                    contract.GetType().GetProperties().FirstOrDefault(p => p.Name == Property.MappedToName);
         if (property != null)
         {
             result = property.GetValue(contract);
         }
      }

      return result;
   }
}

And this is how I want to use it

AutoMapper.Mapper.Map(dataContract, dbModel)

This currently works great but if there is a NULL value in the dataContract then it will replace the existing value in the dbModel, this is not what I want. How do I make AutoMapper ignore null source values?

EDIT

As pointed out in one of the answers there is this

Mapper.CreateMap<SourceType, DestinationType>().ForAllMembers(opt => opt.Condition(srs => !srs.IsSourceValueNull));

This would be ideal except for the fact that .ForAllMembers is not accessible from

Mapper.CreateMap(SourceType, DestinationType)

Possible duplicate of AutoMapper.Map ignore all Null value properties from source object — Michael Freidgeim
– Michael Freidgeim, Commented Apr 10, 2018 at 13:24

Michael Freidgeim · Accepted Answer · 2018-04-10 13:49:39Z

30

UPDATE: IsSourceValueNull is not available starting from V5.

If you want all source properties with null values to be ignored you could use:

Mapper.CreateMap<SourceType, DestinationType>()
  .ForAllMembers(opt => opt.Condition(srs => !srs.IsSourceValueNull));

Otherwise, you can do something similar for each member.

Read this.

edited Apr 10, 2018 at 13:49

Michael Freidgeim

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answered Nov 17, 2013 at 0:50

Prasad Kanaparthi

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5 Comments

Mike Norgate Over a year ago

I've already looked at this and it does not work for the way I'm creating a map. The ForAllMembers is only available when creating a map using CreateMap<>() and you can see from my example I'm not using the generic method as I need to use variables to specify the types.

Neoqq Over a year ago

Hi, can we configure the condition for all classes automatically? Thanks.

Prasad Kanaparthi Over a year ago

@bounces, That is good idea. I am not sure about that. My guess you can use reflection and get all classes and foreach class you can do above logic.

Baama Over a year ago

Am using automapper 6.0.2. the extension IsSourceValueNull does not exist

Tim Over a year ago

I added an answer that works for my project which is using AutoMapper 6.0.2.

Marc Lopez · Accepted Answer · 2016-09-27 18:03:07Z

15

For newer versions that utilize the Instance API, use this instead:

var mappingConfig = new MapperConfiguration(cfg =>
{
    cfg.CreateMap<SourceType, DestinationType>().ForAllMembers(opt => opt.Condition(
        (source, destination, sourceMember, destMember) => (sourceMember != null)));
});

Note: This functionality works as of 5.0.2, breaking on later versions as of this writing. Waiting for the next 5.2.x release is recommended if upgrading from 5.0.2.

edited Sep 27, 2016 at 18:03

answered Sep 26, 2016 at 23:09

Marc Lopez

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2 Comments

Zac Faragher Over a year ago

This doesn't work on 6.1.1 if you're using Nullable<T> to non-nullable T. E.g. Nullable<int> => int - it thinks that the source value is 0 if it's null.

Tim Over a year ago

I added an answer that works for my project which is using AutoMapper 6.0.2.

Tim · Accepted Answer · 2017-07-08 13:15:13Z

The solution here works for my project, which is using AutoMapper 6.0.2. In previous projects using AutoMapper 4, I had used IsSourceValueNull to achieve similar behavior. I have nullable types mapped to non-nullable types in my project, this solution is able to handle that scenario.

I made a small change to the original solution. Instead of checking the type of the property to be mapped, I set the filter in ForAllPropertyMaps to check the type of the source object, so that the custom resolver only applies to maps from that source object. But the filter can be set to anything as needed.

var config = new MapperConfiguration(cfg =>
{
    cfg.ForAllPropertyMaps(
        pm => pm.TypeMap.SourceType == typeof(<class of source object>),
        (pm, c) => c.ResolveUsing<object, object, object, object>(new IgnoreNullResolver(), pm.SourceMember.Name));
});

class IgnoreNullResolver : IMemberValueResolver<object, object, object, object>
{
    public object Resolve(object source, object destination, object sourceMember, object destinationMember, ResolutionContext context)
    {
        return sourceMember ?? destinationMember;
    }
}

Chris Hynes · Accepted Answer · 2014-07-01 17:26:02Z

2

I've got the same exact issue with mapping up the conditionals to the non-generic types. Here's how I solved it.

Wire up:

foreach (PropertyInfo p in type.GetProperties().Where(x => x.GetCustomAttributes<SkipMapIfNullAttribute>().Any()))
    map.ForMember(p.Name, x => x.ResolveUsing(typeof(SkipMapIfNullResolver)).FromMember(p.Name));

The second .FromMember is required so the value for the member is passed to the value resolver, rather than the full model.

The resolver looks like this:

public class SkipMapIfNullResolver : IValueResolver
{
    public ResolutionResult Resolve(ResolutionResult source)
    {
        if (source.Value == null)
            source.ShouldIgnore = true;

        return source;
    }
}

answered Jul 1, 2014 at 17:26

Chris Hynes

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1 Comment

jsgoupil Over a year ago

This works great with a IValueResolver, it doesn't work if you try to use the Func<ResolutionResult, object>. Use source.New(...) if you need to change the resulting value.

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