Skip to main content

AfterMap

As the name suggests, afterMap() sets up a MapCallback to be called after the map operation.

Configure on Mapping​

Pass afterMap() in createMap() to sets up the MapCallback

createMap(
    mapper,
    User,
    UserDto,
    afterMap((source, destination) => {})
);

Configure on map()​

Pass afterMap in MapOptions when calling map() to sets up the MapCallback

mapper.map(user, User, UserDto, {
    afterMap: (source, destination) => {},
});
info
  • afterMap() on map() has precedence over Mapping
  • For mapArray (and its variants), afterMap() on Mapping is ignored because it would be bad for performance if we run afterMap for each and every item of the array. afterMap() on mapArray() will be invoked with (sourceArray, destinationArray) instead

Async Mapping​

One of the common use-cases of afterMap is to execute some asynchronous operation. Let's assume our Destination have some property whose value can only be computed from an asynchronous operation, we can leverage mapAsync() and afterMap() for it.

createMap(
    mapper,
    User,
    UserDto,
    //                  👇 We are fetching the "fullName" manually
    //                  👇          👇 so we need to ignore it
    forMember((d) => d.fullName, ignore()),
    afterMap(async (source, destination) => {
        const fullName = await fetchFullName(source);
        Object.assign(destination, { fullName });
    })
);

//                          👇 mapAsync is needed if we use the above "trick" with afterMap
const dto = await mapper.mapAsync(user, User, UserDto);
caution

Simple asynchronous operations should be fine with this approach. However due to Fake Async, we should NOT use AutoMapper for a particular pair of models if those models require some heavy and complex asynchronous operations.

What about postMap?​

When create the Mapper, we can customize the postMap function on the MappingStrategy. The differences between postMap and afterMap are:

  • postMap runs after every map operation
  • There is only one postMap per Mapper
  • postMap runs AFTER afterMap