Constructor mapping

Custom Destination Object Creation

You can provide a function call to create your destination objects instead of using the default object creation (which expects an empty constructor). To do so, use the ConstructUsing method when configuring. This method expects a function that will provide the destination instance. You can call your own constructor, a factory method, or anything else that provides an object of the expected type.

//Example using a non-default constructor
TypeAdapterConfig<TSource, TDestination>.NewConfig()
    .ConstructUsing(src => new TDestination(src.Id, src.Name));

//Example using an object initializer
TypeAdapterConfig<TSource, TDestination>.NewConfig()
    .ConstructUsing(src => new TDestination{Unmapped = "unmapped"});

//Example using an overload with `destination` parameter
TypeAdapterConfig<TSource, TDestination>.NewConfig()
    .ConstructUsing((src, destination) => new TDestination(src.Id, destination?.Name ?? src.Name));

Map to constructor

By default, Mapster will only map to fields and properties. You can configure to map to constructors by MapToConstructor.

//global level
TypeAdapterConfig.GlobalSettings.Default.MapToConstructor(true);

//type pair
TypeAdapterConfig<Poco, Dto>.NewConfig().MapToConstructor(true);

To define custom mapping, you need to use Pascal case.

class Poco {
    public string Id { get; set; }
    ...
}
class Dto {
    public Dto(string code, ...) {
        ...
    }
}

TypeAdapterConfig<Poco, Dto>.NewConfig()
    .MapToConstructor(true)
    .Map('Code', 'Id'); //use Pascal case

If a class has 2 or more constructors, Mapster will automatically select largest number of parameters that satisfy mapping.

class Poco {
    public int Foo { get; set; }
    public int Bar { get; set; }
}
class Dto {
    public Dto(int foo) { ... }
    public Dto(int foo, int bar) { ...} //<-- Mapster will use this constructor
    public Dto(int foo, int bar, int baz) { ... }
}

Or you can also explicitly pass ConstructorInfo to the method.

var ctor = typeof(Dto).GetConstructor(new[] { typeof(int), typeof(int) });
TypeAdapterConfig<Poco, Dto>.NewConfig()
    .MapToConstructor(ctor);