AutoMapper中用户自定义转换

Posted 2020-09-19 漫思

Custom Type Converters

Sometimes, you need to take complete control over the conversion of one type to another. This is typically when one type looks nothing like the other, a conversion function already exists, and you would like to go from a "looser" type to a stronger type, such as a source type of string to a destination type of Int32.

For example, suppose we have a source type of:

public class Source
{
    public string Value1 { get; set; }
    public string Value2 { get; set; }
    public string Value3 { get; set; }
}

 

But you would like to map it to:

public class Destination
{
    public int Value1 { get; set; }
    public DateTime Value2 { get; set; }
    public Type Value3 { get; set; }
}

 

If we were to try and map these two types as-is, AutoMapper would throw an exception (at map time and configuration-checking time), as AutoMapper does not know about any mapping from string to int, DateTime or Type. To create maps for these types, we must supply a custom type converter, and we have three ways of doing so:

void ConvertUsing(Func<TSource, TDestination> mappingFunction);
void ConvertUsing(ITypeConverter<TSource, TDestination> converter);
void ConvertUsing<TTypeConverter>() where TTypeConverter : ITypeConverter<TSource, TDestination>;

The first option is simply any function that takes a source and returns a destination. This works for simple cases, but becomes unwieldy for larger ones. In more difficult cases, we can create a custom ITypeConverter<TSource, TDestination>:

public interface ITypeConverter<TSource, TDestination>
{
    TDestination Convert(TSource source);
}

 

And supply AutoMapper with either an instance of a custom type converter, or simply the type, which AutoMapper will instantiate at run time. The mapping configuration for our above source/destination types then becomes:

[Test]
public void Example()
{
    Mapper.CreateMap<string, int>().ConvertUsing(Convert.ToInt32);
    Mapper.CreateMap<string, DateTime>().ConvertUsing(new DateTimeTypeConverter());
    Mapper.CreateMap<string, Type>().ConvertUsing<TypeTypeConverter>();
    Mapper.CreateMap<Source, Destination>();
    Mapper.AssertConfigurationIsValid();

    var source = new Source
    {
        Value1 = "5",
        Value2 = "01/01/2000",
        Value3 = "AutoMapperSamples.GlobalTypeConverters.GlobalTypeConverters+Destination"
    };

    Destination result = Mapper.Map<Source, Destination>(source);
    result.Value3.ShouldEqual(typeof (Destination));
}

public class DateTimeTypeConverter : ITypeConverter<string, DateTime>
{
    public DateTime Convert(string source)
    {
        return System.Convert.ToDateTime(source);
    }
}

public class TypeTypeConverter : ITypeConverter<string, Type>
{
    public Type Convert(string source)
    {
        Type type = Assembly.GetExecutingAssembly().GetType(source);
        return type;
    }
}