auto_mappr 1.6.0 | Dart package

Developed with 💚 by netglade

A mapper that maps between different objects with ease. Heavily inspired by C# AutoMapper.

👀 What is this?
- Why should you use it?
🚀 Getting started
✨ Features
⚙ Customizing the build
- Builder options
- Default dependencies
  - Drift integration
👏 Contributing

👀 What is this? #

AutoMappr is a code-generation package that helps with writing object-to-object mappings, so you don't have to write code by hand.

These mappings work by analyzing source and target objects and creating mapping to selected constructor and setter fields. That is done by code generation, which moves mapping overload from runtime to pre-compile time, so your code is as fast, predictable, and debuggable as if you write it yourself.

The only thing you have to do to make it work is create a mappr class and annotate it with a @AutoMappr annotation. Then for each object mapping, set up a mapping between a source and a target type of those objects like this: MapType<Source, Target>(). This set up the automatic mapping of matching fields. Check the getting started section to learn more about the technical details. While AutoMappr has a lot of customizations, it should work in most cases automatically for you. Despite that, you can still configure default values and custom mappings for both objects and fields, ignoring unwanted fields, setting a rename, forcing a selected constructor etc.

Why should you use it? #

Mapping objects to other objects can be for sure done by hand. While it works, it's incredibly boring. Most of the time, object mapping can occur in places like mapping network DTOs from/to domain layer's models, domain layer's models from/to UI models, etc. In other words: if you care about code segregation and single responsibility, you do a lot of mappings. Tools like AutoMappr can help you with reducing boilerplate code and reduce the time you would spend on mapping objects or updating the mappings.

🚀 Getting started #

How to use #

Create a mapping class with @AutoMappr annotation. You will also need to import the annotation. Then use MapType<Source, Target>() for each mapping.

import 'package:auto_mappr_annotation/auto_mappr_annotation.dart';

part 'my_file.g.dart';

@AutoMappr([
  MapType<UserDto, User>(),
])
class Mappr extends $Mappr {}

Depending on your needs, it can also be heavily customized. Below you can see just some of its options. See features for a complete list.

import 'package:auto_mappr_annotation/auto_mappr_annotation.dart';

part 'my_file.g.dart';

@AutoMappr([
  MapType<UserDto, User>(
    fields: [
      Field('address', from: 'userAddress'),
      Field('fullName', custom: Mappr.mapFullName),
      Field('age', custom: 42),
      Field('tag', ignore: true)
    ],
  ),
])
class Mappr extends $Mappr {
  static String mapFullName(UserDto dto) => '${dto.firstName} ${dto.lastName}';
}

To actually use the mappr in your code, call the convert method on it's instance. Note that the convert function has two generic parameters — source and target. AutoMappr uses type inference to determine which mapping to use, therefore you should care about a strict type inference. Either assign the result of converting to an explicitly typed variable or explicitly state generics. The function cannot infer the generic parameters just from the source parameter.

It should look like this:

void main() {
  final mappr = Mappr();

  // convert like this
  User user = mappr.convert(UserDto(...));

  // or like this
  final user2 = mappr.convert<UserDto, User>(UserDto(...));
}

To make the Dart analyzer help you with inference failures, you can set up the analyzer in the analysis_options.yaml file. I would also suggest to use some predefined list of lints and analysis settings such as very_good_analysis or our netglade_analysis.

analyzer:
  language:
    strict-casts: true
    strict-inference: true
    strict-raw-types: true

`convert` vs `tryConvert`

The convert and tryConvert works the same. The only difference is that if a null value is passed inside as the argument, and whenSourceIsNull is not set for the mapping, convert will throw an exception while tryConvert will return null. Therefore, convert has a return type TARGET and tryConvert has a return type TARGET?. It is an analogy with parse and tryParse methods on int.

`try/convert{Iterable, List, Set}`

If you have an iterable of source objects and need to transfer them into an iterable of target objects, use either convertIterable, convertList, or convertSet. What to choose depends on what iterable type you need as an output:

If you need the output as Iterable<Target>, use convertIterable.
If you need the output as List<Target>, use convertList.
If you need the output as Set<Target>, use convertSet.

All of these function also have generics as <SOURCE, TARGET>, where the source and the target are the types of those inner objects.

If you need output of nullable objects in an iterable, use tryConvert{Iterable, List, Set} versions.

Install #

To use AutoMappr, install these three packages:

build_runner -- the tool to run code-generators
auto_mappr -- the AutoMappr code generator
auto_mappr_annotation -- the AutoMappr annotation

For a Flutter project:

flutter pub add auto_mappr_annotation
flutter pub add --dev build_runner
flutter pub add --dev auto_mappr

For a Dart project:

dart pub add auto_mappr_annotation
dart pub add --dev build_runner
dart pub add --dev auto_mappr

Run the generator #

For a Flutter project:

flutter pub run build_runner build

For a Dart project:

dart run build_runner build

✨ Features #

Primitive objects mapping #

Primitive objects like num, int, double, String, bool, Symbol, Type, and null are copied to target object with no additional processing.

Complex objects mapping #

Complex (or nested) objects are mapped according to their MapType<SOURCE, TARGET>() mapping setup. The generator generates mapping methods for each MapType. These mapping methods are used in nested objects.

Field mapping #

When target and source fields' name do not match, you can change source field by using the from argument in a Field() mapping. Alternatively, you can use the Field.from() constructor which hides other then-invalid parameters.

@AutoMappr([
  MapType<UserDto, User>(
    fields: [
      Field('name', from: 'myName'),
      Field.from('age', from: 'myAge'),
    ],
  ),
])
class Mappr extends $Mappr {}

Custom mapping #

When you need to assign a custom function or a const value as a value for given target field, you can use the custom argument in a Field mapping. Alternatively, you can use the Field.custom() constructor which hides other then-invalid parameters.

You can set up Target Function(Source dto) function or const Target value.

@AutoMappr([
  MapType<UserDto, User>(
    fields: [
      Field('name', custom: Mappr.mapName), // Static Mappr method.
      Field('age', custom: mapAge), // Global method.
      Field.custom('note', custom: 'constant value'), // Constant value.
    ],
  ),
])
class Mappr extends $Mappr {
  static String mapName(UserDto dto) => dto.name.toUpperCase();
}

int mapAge(UserDto _) => 42;

Ignore mapping #

To completely ignore some target field, so it is not mapped into a constructor or into a setter, you can use the ignore argument in a Field mapping. Alternatively, you can use the Field.ignore() constructor which hides other then-invalid parameters.

@AutoMappr([
  MapType<UserDto, User>(
    fields: [
      Field('name', ignore: true),
      Field.ignore('age', ignore: true),
    ],
  ),
])
class Mappr extends $Mappr {}

Iterable objects mapping #

Values in iterables like List, Set, or Iterable are mapped using the .map() method when the values are complex types. When needed, mostly after mapping, .toList() or .toSet() methods are called to cast an Iterable into a List/Set.

Specialized variants of `List<int>`

AutoMappr will automatically convert between List<int> and its specialized variants Uint8List, Uint16List, Uint32List and Uint64List.

Convesion between these specialized variants are not handled and its developer responsibility to configure mapping.

Map objects mapping #

Maps are a specific case of Iterables, that has to be handled a bit differently. For example, we must make sure that both keys and values of MapEntry are mapped correctly based on whether they are primitive or complex types.

Default field value #

To make sure that a default value is assigned to a target field when a source field is null you can set up a whenNull property on Field which takes a constant value of target field type.

You can set up default field value by using Target Function() function or const Target value on Field, Field.from, and Field.custom, constructors but not on Field.ignore constructor.

@AutoMappr([
  MapType<UserDto, User>(
    fields: [
      Field('name', whenNull: 'John Smith'),
    ],
  ),
])
class Mappr extends $Mappr {}

Default object value #

When the whole source object is null, you can set up a default value for it using the whenSourceIsNull property on MapType. It can also take a constant value of target object type.

You can set up Target Function() function or const Target value.

@AutoMappr([
  MapType<UserDto, User>(
    whenSourceIsNull: User(name: 'Neo', age: 28),
  ),
])
class Mappr extends $Mappr {}

Constructor selection #

When you want to specifically select a certain constructor, set the constructor property on MapType. Otherwise the mapping automatically selects a constructor with the most parameters. It prioritizes non factory constructors over factory ones and never selects fromJson factory constructor.

Imagine that you have a User(String name, int age, String note) and User.fromDto(String name, int age) constructors. Default algorithm selects the default constructor because it has the most parameters. To change the selected constructor, do:

@AutoMappr([
  MapType<UserDto, User>(
    constructor: 'fromDto',
  ),
])
class Mappr extends $Mappr {}

Enum mapping #

AutoMappr also supports mapping of enums. You register them as usual with MapType<SourceEnum, TargetEnum> and AutoMappr will convert enum options based on name.

The target enum can either be a superset of the source or has to define whenSourceIsNull which will be used for unknown enum values. If the target is not a superset of the source enum the generator will throw.

E.g. in the example below, RemotePerson.alien will be mapped to LocalPerson.unknown.

enum RemotePerson { student, employee, alien }
enum LocalPerson { student, employee, unknown }

@AutoMappr([
  MapType<RemotePerson, LocalPerson>(
    whenSourceIsNull: LocalPerson.unknown,
  ),
])
class Mappr extends $Mappr {}

Mapping works for both simple and enhanced enums.

Positional and named constructor parameters #

The mapping automatically assigns source getters to constructor parameters no matter if they are positional or named.

Mapping to target #

Mapping into a target object can be done in two places. First, the mapping tries to map all the fields to selected constructor. And for the target fields that have not been mapped, it tries to set them using public setters (both explicit ones or implicit ones created by fields), if they have any.

Mapping from source #

Mapping from a source object can be done from either public getters or static getters. Getters can be both explicit ones or implicit ones created by fields.

Nullability handling #

For each MapType<SOURCE, TARGET>() mapping the generator generates at most two mapping methods. First method is a method with non-nullable return type TARGET. Second method is a method with nullable return type TARGET? that is being generated only when other methods use it. If the object mapping has whenSourceIsNull parameter set, the nullable method is not generated.

Note that convert cannot return null. The value null can only be returned for nested object mappings.

Forced non-nullable field for nullable source

It is possible to configure automappr use bang operator (!) in cases where SOURCE's field is nullable but TARGET's field not. In that case mappr will generate

sourceField: targetField!

By default mappr would generate invalid code

sourceField: targetField

This is by design and it is up to developer decide if bang operator is appropiate. This behavior can be configured

Globally, via build.yaml with option ignoreNullableSourceField

 $default:
  builders:
    :auto_mappr:
      options:
        ignoreNullableSourceField: true

On MapType with ignoreFieldNull
On Field level with ignoreNull

Precedense is global configuration -> MapType -> Field -> defaults to false.

Generics #

AutoMappr can handle generics, so you can map objects with type arguments with ease.

@AutoMappr([
  MapType<SomeObjectDto<num>, SomeObject<num>>(),
  MapType<SomeObjectDto<int>, SomeObject<int>>(),
  MapType<SomeObjectDto<String>, SomeObject<String>>(),
])
class Mappr extends $Mappr {}

Type parameters are not limited. You can use them as a direct type, in a nested object types, in collections, ... AutoMappr will automatically handles them for you.

class Something<A, B, C> {
  final A first;
  final Nested<A, B> second;
  final List<C> third;
  final List<Nested<A, C>> fourth;
// ...
}

class Nested<X, Y> {
  final X alpha;
  final Y beta;
// ...
}

Library import aliases #

In cases when you have two libraries with classes with the same name, mapping works as expected by using import aliases.

import 'my_api.dart' as api;
import 'my_domain.dart' as entity;

@AutoMappr([
  MapType<api.User, entity.User>(),
])
class Mappr extends $Mappr {}

Note that importing a list of MapType from another library and putting it inside @AutoMappr annotation is not possible, since we cannot generate the type correctly (it can overlap with something else) while using shared part builder.

Modules #

Each AutoMappr class can be used as a module. That means a mappr used inside of another mappr. Each AutoMappr class can include a list of modules that can be used to nest modules and use all of its underlying mappings.

Note that modules work as disjunctive units and their mappings cannot be internally used by by mappr that imported it. They only work for grouping at the moment.

Applications are often split into independent parts (we will call them features). Each feature should probably have its own independent mappr, that is used as a module.

Imagine that in a feature you have a local mappr UserMappr.

// file: user_mappr.dart
@AutoMappr([
  MapType<UserDto, User>(),
])
class UserMappr extends $UserMappr {
  const UserMappr(); // must implement const constructor
}

And in some global place, you can have a main mappr that unifies all smaller mapprs (UserMappr in this case). As usual, it can also set it's own mappings (MapType<GroupDto, Group>()).

// file: main_mappr.dart
@AutoMappr(
  [
    MapType<GroupDto, Group>(),
  ],
  modules: [
    UserMappr(), // use module
  ],
)
class MainMappr extends $MainMappr {}

Then you can use this main mappr to map between objects specified from every included mappr.

final mappr = MainMappr();

final Group user = mappr.convert(GroupDto(...)); // from this mappr
final User user = mappr.convert(UserDto(...)); // from included mappr

That can be handy for example with dependency injection, so you can only provide one grouping/main mappr that can handle everything. Each feature in your app can return an instance of const AutoMapprInterface, that each mappr internally implements.

Works with `equatable` #

Mapping works with the Equatable package. Some mapping tools tries to map the props getter, but since AutoMappr maps only to public explicit or implicit setters, Equatable and other packages with similar conditions implicitly works.

Works with `json_serializable` #

AutoMappr uses a SharedPartBuilder. That means it can share the .g.dart file with packages like JSON Serializable to generate other code to the generated super class.

Works with generated source and target classes #

Mapping can be set up for source or target classes which are generated by another package, like Drift. For that, you have to customize a builder to set custom dependencies on the other package's outputs.

You can also use this package as an output for another package's builder. Disable the default auto_mappr builder and enable the auto_mappr:not_shared builder. Check the customizing the build chapter to learn more.

⚙ Customizing the build #

By default, AutoMappr uses the auto_mappr:auto_mappr builder that works with SharedPartBuilder, which generates combined .g.dart files. If you need to use PartBuilder to generate not-shared .auto_mappr.dart part files, you can use the auto_mappr:not_shared builder.

Modify your build.yaml file:

targets:
  $default:
    # You can disable all default builders.
    auto_apply_builders: false
    builders:
      # Or disable specific ones.
      auto_mappr:
        enabled: false
      # And enable the not_shared builder.
      auto_mappr:not_shared:
        enabled: true

Builder options #

ignoreNullableSourceField - Force bang operator on non-nullable target's field if source's field is nullable

Default dependencies #

By default both auto_mappr builders has defined required inputs for freezed and drift classes.

 required_inputs: [".freezed.dart", ".drift.dart"]

This allows to depend on generated classes from these packages without need to modify project's build.yaml.

Drift integration

If you are using packages like Drift which generates classes you need to use as a source or a target in your mappings, use their not-shared builder, if they have any. With that, the builder can generate files like .drift.dart which you can add a input dependency to. Specify the required_inputs dependency on your local AutoMappr builder and disable the builders provided by AutoMappr.

Shared builder:

targets:
  $default:
    auto_apply_builders: true
    builders:
      # Enable their generators according to their documentation.
      drift_dev:not_shared:
        enabled: true
      drift_dev:preparing_builder:
        enabled: true
      # Disable Drift's shared builder
      drift_dev:drift_dev:
        enabled: false

Not shared builder:

targets:
  $default:
    auto_apply_builders: true
    builders:
      # Enable their generators according to their documentation.
      drift_dev:not_shared:
        enabled: true
      drift_dev:preparing_builder:
        enabled: true
      # Disable Drift's shared builder
      drift_dev:drift_dev:
        enabled: false

      auto_mappr:
        enabled: false
      # Enable the not_shared builder.
      auto_mappr:not_shared:
        enabled: true

👏 Contributing #

Your contributions are always welcome! Feel free to open pull request.

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