AutoMapper.ExtendedConverters

AutoMapper.ExtendedConverters is a small set of useful AutoMapper (and Mapster) custom Type Converters

ListConverter and more general CollectionConverter are usefull for updating data in existing collections.

For example, we have list of entites from database and it's modified version from client. Then with ListConverter we can update all database entities from client objects with same Id.

using AutoMapper;
using AutoMapper.ExtendedConverters;

class Model
{
    public int Id { get; set; }
    public string Text { get; set; }
}

class Entity
{
    public int Id { get; set; }
    public string Text { get; set; }
}

class Program
{
    static IMapper Mapper;
    
    static void Configure()
    {
        var config = new MapperConfiguration(cfg =>
        {
            cfg.CreateMap<Model, Entity>();
            // create custom mapper for lists
            cfg.CreateMap<List<Model>, List<Entity>>()
                // configure 'Id' property selectors for Model and Entity
                .UsingListConverter(m => m.Id, e => e.Id);
        });
        
        Mapper = config.CreateMapper();
    }
    
    static void Main()
    {
        // values from Server
        var dest = new List<Entity>
        {
            new Entity { Id = 1, Text = "a" },
            new Entity { Id = 2, Text = "b" },
        };
        // values from Client
        var src = new List<Model>
        {
            new Model { Id = 1, Text = "A" },
            new Model { Id = 3, Text = "C" },
        };
        
        List<Entity> res = Mapper.Map(src, dest);
        
        // now res is equivalent to
        new List<Entity>
        {
            // Entity with Id == 1 is updated
            new Entity { Id = 1, Text = "A" },
            // Entity with Id == 2 is removed
            // ...
            // Entity with Id == 3 is added
            new Entity { Id = 3, Text = "C" },
        }
    }
}

Mapping collections other than List<T>

var config = new MapperConfiguration(cfg =>
{
    cfg.CreateMap<IEnumerable<Model>, ICollection<Entity>>()
        .UsingCollectionConverter((Model m) => m.Id, (Entity e) => e.Id);
});   

Using with Mapster

using Mapster;
using Mapster.CollectionChangeTracking;

class Model
{
    public int Id { get; set; }
    public string Text { get; set; }
}

class Entity
{
    public int Id { get; set; }
    public string Text { get; set; }
}

class Program
{
    static void Configure()
    {
        TypeAdapterConfig<List<Model>, List<Entity>>.NewConfig()
            .TrackListChanges(m => m.Id, e => e.Id);
        
        // for mapping collections other than lists
        TypeAdapterConfig<Model[], SortedSet<Entity>>.NewConfig()
            .TrackCollectionChanges((Model m) => m.Id, (Entity e) => e.Id);
    }
    
    static void Main()
    {
        // values from Server
        var dest = new List<Entity>
        {
            new Entity { Id = 1, Text = "a" },
            new Entity { Id = 2, Text = "b" },
        };
        // values from Client
        var src = new List<Model>
        {
            new Model { Id = 1, Text = "A" },
            new Model { Id = 3, Text = "C" },
        };
        
        List<Entity> res = TypeAdapter.Adapt(src, dest);
        
        // now res is equivalent to
        new List<Entity>
        {
            // Entity with Id == 1 is updated
            new Entity { Id = 1, Text = "A" },
            // Entity with Id == 2 is removed
            // ...
            // Entity with Id == 3 is added
            new Entity { Id = 3, Text = "C" },
        }
    }
}