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)

Answer 1

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.

Answer 2

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.