Mappings and transformations

Learn how mappings relate source and destination identifiers and how destination members are transformed.

A Mapping is a unidirectional contract between source and destination identifiers. Create each direction explicitly:

createMap(mapper, User, UserDto);
createMap(mapper, UserDto, User);

Each source/destination pair is unique within a mapper. You can also create a self mapping by using one identifier.

Destination-member transformations

Mapping configuration defines how each destination path receives its value. Public member functions include:

Function	Purpose
`ignore()`	Leave a destination member unmapped
`mapFrom()`	Select or resolve a value from the source
`condition()`	Map only when a predicate succeeds
`fromValue()`	Assign a fixed value
`mapWith()`	Map a nested value with explicit model identifiers
`convertUsing()`	Convert a selected source value with a reusable converter
`nullSubstitution()`	Replace a `null` source value
`undefinedSubstitution()`	Replace an `undefined` source value
`mapWithArguments()`	Resolve a member using invocation-time arguments
`mapDefer()`	Choose a member function at mapping time

forMember() associates one of these functions with a selected destination path:

forMember(
  (destination) => destination.displayName,
  mapFrom((source) => `${source.firstName} ${source.lastName}`),
);

Use mapping profiles to organize related mapping declarations and share configuration across them.