MyLittleSuite/dart_mapperdart_mapper

Collections

Map List, Set, Iterable, Map, and Built Collection fields automatically.

Collections

dart_mapper maps collection fields automatically. When element types need conversion (e.g., CustomSource → CustomTarget), the generator calls the appropriate mapper method for each element.

Primitive Collections

Collections of primitive types (int, String, bool, etc.) are passed through directly:

class Source {
  final List<int> integers;
  final Set<String> labels;
  final Map<String, int> metadata;
  final Iterable<int> counts;
  Source({required this.integers, required this.labels, required this.metadata, required this.counts});
}

class Target {
  final List<int> integers;
  final Set<String> labels;
  final Map<String, int> metadata;
  final Iterable<int> counts;
  Target({required this.integers, required this.labels, required this.metadata, required this.counts});
}

@Mapper()
abstract class DataMapper {
  Target toTarget(Source source);
}

Generated:

@override
Target toTarget(Source source) {
  return Target(
    integers: source.integers,
    labels: source.labels,
    metadata: source.metadata,
    counts: source.counts,
  );
}

Object Element Conversion

When element types differ, the generator looks for a mapper method converting the element type and calls it per element:

class ItemSource { final String name; const ItemSource(this.name); }
class ItemTarget { final String name; const ItemTarget(this.name); }

class Container {
  final List<ItemSource> items;
  const Container({required this.items});
}

class ContainerDto {
  final List<ItemTarget> items;
  const ContainerDto({required this.items});
}

@Mapper()
abstract class ContainerMapper {
  ContainerDto toDto(Container container);
  ItemTarget toItemTarget(ItemSource source);
}

Generated:

@override
ContainerDto toDto(Container container) {
  return ContainerDto(
    items: container.items.map(toItemTarget).toList(),
  );
}

Map Fields

Map fields with object value types also resolve element mapping automatically:

class ItemMap {
  final Map<String, ItemSource> catalog;
  const ItemMap({required this.catalog});
}

class ItemMapDto {
  final Map<String, ItemTarget> catalog;
  const ItemMapDto({required this.catalog});
}

@Mapper()
abstract class CatalogMapper {
  ItemMapDto toDto(ItemMap source);
  ItemTarget toItemTarget(ItemSource source);
}

Generated:

@override
ItemMapDto toDto(ItemMap source) {
  return ItemMapDto(
    catalog: source.catalog.map((k, v) => MapEntry(k, toItemTarget(v))),
  );
}

Built Collections (built_collection)

BuiltList<T>, BuiltSet<T>, and BuiltMap<K, V> are treated like their standard Dart equivalents. The generator converts between standard and built collections as needed:

// Standard → BuiltList
// source.members.toBuiltList()  (or via builder .members.addAll(...))

// BuiltList → Standard List
// source.members.toList()

See Built Value support guide for full setup instructions.

Collection Type Coercion

The generator handles mismatched but compatible collection types:

Source typeTarget typeGenerated conversion
List<T>Set<T>.toSet()
Set<T>List<T>.toList()
Iterable<T>List<T>.toList()
List<T>Iterable<T>direct assignment
List<T>BuiltList<T>.toBuiltList()
BuiltList<T>List<T>.toList()

See Also

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Built Value Support