How to ignore mapping source null values globally?

Question

Is there a way to ignore mapping null values to destination globally (for all mapping configurations)?

Something that goes in here:

    //Automapper config
    Mapper.Initialize(cfg =>
    {
        //Initializes all mapping profiles in the assembly
        cfg.AddProfiles(Assembly.GetExecutingAssembly().GetName().Name);

        //If map is called without a profile creates default map
        cfg.CreateMissingTypeMaps = true;
    });

This is for instance mapping. Here is one example of what i'm trying to accomplish.

//Models
    class User {
      public string Name {get; set;}
      public string Email {get; set;}
      public string Password {get; set;}
    }

    class UserDto {
      public string Name {get; set;}
      public string Email {get; set;}
    }

//Start instances
     var user = new User { Name = "John", Email = "[email protected]", Password = "123"};

     var userDto = new UserDto { Name = "Tim" };
//Notice that we left the Email null on the DTO


//Mapping
    Mapper.Map(userDto, user);

The result ends up with the user having a null email. I want the user email to not be changed unless a new email is provided on the source (userDto). In other words ignore all null properties of all types on the source object from overwriting destination (User)

UPDATE: None of the answers below solve the problem. They simply do not work for collections. While the Autommaper figures out this bug I was able to get around my problem by using an ExpandoObject to filter out all null properties before mapping as below:

var patchInput = new ExpandoObject() as IDictionary<string, object>;

foreach (var property in userDto.GetType().GetProperties())
    if (property.GetValue(userDto) is var propertyValue && propertyValue != null)
        patchInput.Add(property.Name, propertyValue);

Mapper.Map(patchInput, user);

Possible duplicate of Automapper skip null values with custom resolver — xenteros
– xenteros, Commented Sep 26, 2017 at 14:24
@Valerii Added the part where the config should go above. not sure if thats what you wanted. — DonO
– DonO, Commented Sep 26, 2017 at 17:25
@DonO Thanks. Can you also explain phrase "ignore mapping null values to destination". What behavior do you expect? — Valerii
– Valerii, Commented Sep 26, 2017 at 17:29

Valerii · Accepted Answer · 2017-09-26 20:25:03Z

1

It should work

Mapper.Initialize(cfg =>
        {
            cfg.AddProfiles(Assembly.GetExecutingAssembly().GetName().Name);
            cfg.CreateMissingTypeMaps = true;
            cfg.ForAllMaps((typeMap, map) =>
                map.ForAllMembers(option => option.Condition((source, destination, sourceMember) => sourceMember != null)));
        });

answered Sep 26, 2017 at 20:25

Valerii

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8 Comments

DonO Over a year ago

This answers my question but it seems that the other conditions defined on individual mapping profiles no longer work. :\

Valerii Over a year ago

@DonO It works for Nulable numbers like int?, for value types like int it won't work because value cannot be null.

Valerii Over a year ago

@DonO For collections it is a defect in AutoMapper. For collections you can use my alternative solution. cfg.CreateMap<IEnumerable, IEnumerable>().ConvertUsing(new IgnoringNullValuesTypeConverter<IEnumerable>());

Valerii Over a year ago

@DonO Why unaccepted? It works for example you provided.

DonO Over a year ago

@Valerri CreateMap<IEnumerable, IEnumerable>().ConvertUsing(new IgnoringNullValuesTypeConverter<IEnumerable>()); wont work because it needs to be IEnumerable<T> but the problem is the types of collections aren't the same.

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