advanced: type converters

Advanced topic: type converters

Standard mapping is very useful in many situations. However, there are some scenarios in which mapping will not provide the expected result. That is where custom type converters come to play.

The createMap.convertUsing function specifies a custom type converter to be used when mapping a source to a destination. Using this function means skipping normal member mapping and converting using a custom type converter. This type converter will be instantiated (when using a class) or executed (when using a function) during mapping.

The actual function used (whether using a class or a function) has to specify one resolutionContext parameter of interface type AutoMapperJs.IResolutionContext. Failing this condition will cause mapping to fail.

Usage samples

Specified as a function

var objA = { propA: 'propA' };

var fromKey = '{D1534A0F-6120-475E-B7E2-BF2489C58571}';
var toKey = '{1896FF99-1A28-4FE6-800B-072D5616B02D}';

automapper
	.createMap(fromKey, toKey)
	.convertUsing(function (resolutionContext : AutoMapperJs.IResolutionContext) {
		return { propA: resolutionContext.sourceValue.propA + ' (custom mapped with resolution context)' }
	});

// act
var objB = automapper.map(fromKey, toKey, objA);

// assert
expect(objB.propA).toEqual(objA.propA + ' (custom mapped with resolution context)');

Specified as a class

Class definition sample:

class CustomTypeConverter extends AutoMapperJs.TypeConverter {
    public convert(resolutionContext: AutoMapperJs.IResolutionContext): any {
        return { propA: resolutionContext.sourceValue.propA + ' (convertUsing with a class definition)' };
    }
}

Usage:

// arrange
var objA = { propA: 'propA' };

var fromKey = '{6E7F5757-1E55-4B55-BB86-44FF5B33DE2F}';
var toKey = '{8521AE41-C3AF-4FCD-B7C7-A915C037D69E}';

automapper
	.createMap(fromKey, toKey)
	.convertUsing(CustomTypeConverter);

// act
var objB = automapper.map(fromKey, toKey, objA);

// assert
expect(objB.propA).toEqual(objA.propA + ' (convertUsing with a class definition)');