luthor_generator

luthor_generator is a package allowing you to generate luthor schemas with code generation. It is a companion to the luthor package, and works with json_serializable, freezed, dart_mappable and hand-written fromJson factories.

Features

• Schema Generation - Automatically generate validation schemas from annotated classes
• Type-safe SchemaKeys - Generated constants for defining schemas with compile-time safety
• Type-safe ErrorKeys - Generated constants for accessing validation errors with dot-notation support
• Cross-field Validation - Support for @WithSchemaCustomValidator to validate fields against other fields

Generated Code

For each class annotated with @luthor, luthor_generator creates:

• $ClassNameSchema - The validation schema, a final SchemaValidator top-level variable named with withName('ClassName')
• ClassNameSchemaKeys - Type-safe keys for schema field access
• ClassNameErrorKeys - Type-safe keys for error handling. A nested model field is a record whose $key is the field's own key, for example UserErrorKeys.address.$key and UserErrorKeys.address.street
• $ClassNameValidate() - Validates any input, such as decoded JSON, and converts it with fromJson (or ClassNameMapper.fromMap for dart_mappable). It returns a ValidationResult<ClassName>
• validateSelf() - An extension method that validates an instance. It is generated only when the class has a toJson method (including the one freezed generates) or is a dart_mappable class

A model needs a fromJson factory, constructor or static method, or a @MappableClass annotation. The schema follows the constructor the serializer uses: the one named in @JsonSerializable(constructor: ...), the @MappableConstructor, the unnamed constructor, or else the first public constructor with parameters.

Classes used by a model's fields but not annotated with @luthor get a private schema (_$ClassNameSchema) in the library that uses them. Nested schemas are always referenced lazily, so recursive and mutually recursive models work without @luthorForwardRef, which is deprecated, still accepted, and has no effect.

No build.yaml is needed. The builder applies source_gen's combining builder itself, so you only need a part 'file.g.dart'; directive, even when you don't use json_serializable.

Field keys and annotations

Validation annotations can sit on the constructor parameter or on the field, including fields reached through super. parameters. Schema keys follow the serializer:

• @JsonKey(name: ...) and @JsonSerializable(fieldRename: ...), on the class or, for freezed, on the factory constructor
• @MappableField(key: ...) and @MappableClass(caseStyle: ...)

Fields excluded with @JsonKey(includeFromJson: false) are left out of the schema. Fields with a constructor default, a freezed @Default or a @JsonKey(defaultValue: ...) are optional.

For a @JsonSerializable class, public fields with a setter that are not constructor parameters are schema fields too, since json_serializable assigns them after calling the constructor. They are required unless they are nullable or have a @JsonKey(defaultValue: ...).

Unknown keys

A generated schema strips keys it doesn't declare before fromJson runs, so every key the serializer reads must be a schema field. When the generator cannot name every key the serializer may read, the schema keeps unknown keys with .passthrough() instead:

• A field with @JsonKey(readValue: ...), whose function receives the whole map. The field itself is validated as an optional l.any().
• A private field with @JsonKey(includeFromJson: true), since a record field in SchemaKeys cannot be private.
• A @MappableClass(hook: ...), whose hook may read the whole map.

A hand-written fromJson must read only the keys of its constructor parameters, or the settable fields above.

Global options in another builder's build.yaml, such as json_serializable's field_rename, are not read. Put them on the class.

An annotation on a field type it doesn't apply to, such as @IsEmail on an int or @HasLength on a List, fails generation. Validation annotations are applied in the order they are written.

Supported field types

Dart type	Validator
String, int, double, num, bool	l.string(), l.int(), l.double(), l.num(), l.bool()
DateTime	l.string().dateTime()
Uri	l.string()
Enums	l.oneOf([...]) with the serialized values, honouring @JsonValue, @JsonEnum(fieldRename:, valueField:), @MappableEnum and @MappableValue
List, Set, Iterable	l.list(element)
Map	l.map() with key and value validators
dynamic, Object, Object?	l.any()
File (dart:io), XFile (cross_file)	l.file()
A class with @luthor, a fromJson or @MappableClass	Its schema

JSON object keys are always strings, so Map keys of type int, double, num and BigInt are validated as strings that parse to that type, with l.string().custom((key) => int.tryParse(key) != null). DateTime, Uri, enum (l.oneOf() of the serialized values as strings) and String keys are also supported. A key that fails is reported as an invalid key of the map.

A json_serializable enum field with @JsonKey(unknownEnumValue: ...) generates l.string() instead of l.oneOf([...]), because json_serializable maps a value it does not know to the fallback instead of throwing. On a List, Set or Iterable of an enum, this applies to each element. An enum whose serialized values are integers generates l.int(). Non-nullable fields still get .required().

A double field generates l.double(), which rejects JSON integers. If your backend may send 1 instead of 1.0, type the field as num.

A field with a JsonConverter (on the field, on the class, or in @JsonSerializable(converters: ...)) or a @JsonKey(fromJson: ...) function is validated as l.any(), because luthor cannot know the shape of the raw JSON value. Only @WithCustomValidator and @WithSchemaCustomValidator apply to such fields.

Not supported yet

These fail generation with an error that names the class or field:

• freezed unions (classes with more than one redirecting factory)
• Generic models, and fields whose type is a generic class or a type parameter
• Records, function types and types without a luthor validator, such as Duration or BigInt values (give these a JsonConverter)
• Validators for list elements (#71)

See the documentation for more information.