Add option to drop nullable values in "toJson"

examples/file_generation_mode/data_class_plugin_options.yaml

@@ -1,6 +1,12 @@
 # default config
 auto_delete_code_from_annotation: false
 
+json:
+  to_json:
+    options_config:
+      drop_null_values:
+        default: true
+
 data_class:
   options_config:
     # default config

examples/file_generation_mode/lib/data_class/to_json/simple.gen.dart

@@ -30,7 +30,7 @@ class _$UserImpl extends User {
     return <String, dynamic>{
       'id': id,
       'username': username,
-      'email': email,
+      if (email != null) 'email': email,
       'isVerified': isVerified,
     };
   }

package/README.md

@@ -289,7 +289,7 @@ To create a custom configuration you need to add a file named `data_class_plugin
    ```
 
    When `auto_delete_code_from_annotation` is `true` => `toJson` will be removed because is set as `false` in the `@DataClass`.
-   
+
    When `auto_delete_code_from_annotation` is `false` => `toJson` will be kept as it is even when `toJson` is set as `false` in the `@DataClass`. This allows to create custom `fromJson/toJson` implementations.
 
 1. `json`
@@ -333,6 +333,19 @@ json:
       - "a/glob/here"
       - "another/glob/here"
 
+  # Allows to configure "toJson" code generation
+  # If no config is provided, null values will be dropped by default
+  to_json:
+    options_config:
+      drop_null_values:
+        default: boolean # default value is there is no match in enabled or disabled lists
+        enabled: # list of globs
+          - "a/glob/here"
+          - "another/glob/here"
+        disabled: # list of globs
+          - "a/glob/here"
+          - "another/glob/here"
+
 data_class:
   options_config:
     # For each of the provided methods you can provide a configuration

package/lib/src/backend/code_generator.dart

@@ -185,6 +185,7 @@ class DataClassPluginGenerator extends TachyonPluginCodeGenerator {
           jsonKeyNameConventionGetter: jsonKeyNameConventionGetter,
           classDeclarationFinder: declarationFinder.findClassOrEnum,
           logger: logger,
+          dropNullValues: pluginOptions.json.toJson.effectiveDropNullValues(targetFileRelativePath),
         ).execute();
       }
 
@@ -420,6 +421,8 @@ class DataClassPluginGenerator extends TachyonPluginCodeGenerator {
             toJsonUnionKey: unionAnnotationValueExtractor.getString('unionJsonKey'),
             classDeclarationFinder: declarationFinder.findClassOrEnum,
             logger: logger,
+            dropNullValues:
+                pluginOptions.json.toJson.effectiveDropNullValues(targetFileRelativePath),
           ).execute();
         }
 

package/lib/src/backend/core/generators/to_json.dart

@@ -10,12 +10,14 @@ class ToJsonGenerator implements Generator {
     required final List<DeclarationInfo> fields,
     required final JsonKeyNameConventionGetter jsonKeyNameConventionGetter,
     required final ClassOrEnumDeclarationFinder classDeclarationFinder,
+    required final bool dropNullValues,
     final String? toJsonUnionKey,
     required final Logger logger,
   })  : _codeWriter = codeWriter,
         _fields = fields,
         _jsonKeyNameConventionGetter = jsonKeyNameConventionGetter,
         _classDeclarationFinder = classDeclarationFinder,
+        _dropNullValues = dropNullValues,
         _toJsonUnionKey = toJsonUnionKey,
         _logger = logger;
 
@@ -24,6 +26,7 @@ class ToJsonGenerator implements Generator {
   final JsonKeyNameConventionGetter _jsonKeyNameConventionGetter;
   final ClassOrEnumDeclarationFinder _classDeclarationFinder;
   final String? _toJsonUnionKey;
+  final bool _dropNullValues;
   final Logger _logger;
 
   @override
@@ -82,6 +85,10 @@ class ToJsonGenerator implements Generator {
           jsonKeyNameConvention.transform(fieldName.escapeDollarSign());
       final TachyonDartType dartType = field.type?.customDartType ?? TachyonDartType.dynamic;
 
+      if (_dropNullValues && dartType.isNullable) {
+        _codeWriter.writeln('if ($fieldName != null)');
+      }
+
       _codeWriter.write("'$jsonFieldName': ");
 
       if (customJsonConverter != null) {
@@ -112,6 +119,9 @@ class ToJsonGenerator implements Generator {
   void _writeNullableParsingPrefix({
     required final String parentVariableName,
   }) {
+    if (_dropNullValues) {
+      return;
+    }
     _codeWriter.write('$parentVariableName == null ? null : ');
   }
 
@@ -174,7 +184,11 @@ class ToJsonGenerator implements Generator {
 
     if (typeDeclarationNode is ClassDeclaration && typeDeclarationNode.hasMethod('toJson') ||
         typeDeclarationNode is EnumDeclaration && typeDeclarationNode.hasMethod('toJson')) {
-      final String accessOperator = dartType.isNullable ? '?.' : '.';
+      final String accessOperator = switch (dartType.isNullable) {
+        true when _dropNullValues => '!.',
+        true => '?.',
+        false => '.',
+      };
       _codeWriter.writeln('$parentVariableName${accessOperator}toJson(),');
       return;
     }

package/lib/src/options/extensions.dart

@@ -49,6 +49,10 @@ extension OptionsGlobMatch on Map<String, OptionConfig> {
     return _effectiveValue('when', filePath, defaultValue);
   }
 
+  bool effectiveToJsonDropNullValues({required String filePath, required bool defaultValue}) {
+    return _effectiveValue('drop_null_values', filePath, defaultValue);
+  }
+
   bool _effectiveValue(
     String method,
     String filePath,

package/lib/src/options/json_options.dart

@@ -1,4 +1,7 @@
 import 'package:data_class_plugin/data_class_plugin.dart';
+import 'package:data_class_plugin/src/options/data_class_plugin_options.dart';
+import 'package:data_class_plugin/src/options/extensions.dart';
+import 'package:data_class_plugin/src/options/options_config.dart';
 
 part 'json_options.gen.dart';
 
@@ -10,6 +13,7 @@ abstract class JsonOptions {
   const factory JsonOptions({
     String? keyNameConvention,
     Map<String, List<String>> nameConventionGlobs,
+    ToJsonOptions toJson,
   }) = _$JsonOptionsImpl;
 
   /// Creates an instance of [JsonOptions] from [json]
@@ -20,4 +24,26 @@ abstract class JsonOptions {
   @JsonKey(name: 'key_name_conventions')
   @DefaultValue(<String, List<String>>{})
   Map<String, List<String>> get nameConventionGlobs;
+
+  @DefaultValue(ToJsonOptions())
+  ToJsonOptions get toJson;
+}
+
+@DataClass()
+abstract class ToJsonOptions {
+  const ToJsonOptions.ctor();
+
+  /// Creates an instance of [ToJsonOptions] from [json]
+  factory ToJsonOptions.fromJson(Map<dynamic, dynamic> json) = _$ToJsonOptionsImpl.fromJson;
+
+  /// Default constructor
+  const factory ToJsonOptions({
+    Map<String, OptionConfig> optionsConfig,
+  }) = _$ToJsonOptionsImpl;
+
+  @DefaultValue(<String, OptionConfig>{})
+  Map<String, OptionConfig> get optionsConfig;
+
+  bool effectiveDropNullValues(String filePath) =>
+      optionsConfig.effectiveToJsonDropNullValues(filePath: filePath, defaultValue: true);
 }

package/lib/src/options/json_options.gen.dart

@@ -9,6 +9,7 @@ class _$JsonOptionsImpl extends JsonOptions {
   const _$JsonOptionsImpl({
     this.keyNameConvention,
     Map<String, List<String>> nameConventionGlobs = const <String, List<String>>{},
+    this.toJson = const ToJsonOptions(),
   })  : _nameConventionGlobs = nameConventionGlobs,
         super.ctor();
 
@@ -20,6 +21,9 @@ class _$JsonOptionsImpl extends JsonOptions {
       Map<String, List<String>>.unmodifiable(_nameConventionGlobs);
   final Map<String, List<String>> _nameConventionGlobs;
 
+  @override
+  final ToJsonOptions toJson;
+
   factory _$JsonOptionsImpl.fromJson(Map<dynamic, dynamic> json) {
     return _$JsonOptionsImpl(
       keyNameConvention: json['key_name_convention'] as String?,
@@ -32,9 +36,38 @@ class _$JsonOptionsImpl extends JsonOptions {
                   for (final dynamic i1 in (e0.value as List<dynamic>)) i1 as String,
                 ],
             },
+      toJson:
+          json['to_json'] == null ? const ToJsonOptions() : ToJsonOptions.fromJson(json['to_json']),
     );
   }
 
   @override
   Type get runtimeType => JsonOptions;
 }
+
+class _$ToJsonOptionsImpl extends ToJsonOptions {
+  const _$ToJsonOptionsImpl({
+    Map<String, OptionConfig> optionsConfig = const <String, OptionConfig>{},
+  })  : _optionsConfig = optionsConfig,
+        super.ctor();
+
+  @override
+  Map<String, OptionConfig> get optionsConfig =>
+      Map<String, OptionConfig>.unmodifiable(_optionsConfig);
+  final Map<String, OptionConfig> _optionsConfig;
+
+  factory _$ToJsonOptionsImpl.fromJson(Map<dynamic, dynamic> json) {
+    return _$ToJsonOptionsImpl(
+      optionsConfig: json['options_config'] == null
+          ? const <String, OptionConfig>{}
+          : <String, OptionConfig>{
+              for (final MapEntry<dynamic, dynamic> e0
+                  in (json['options_config'] as Map<dynamic, dynamic>).entries)
+                e0.key as String: OptionConfig.fromJson(e0.value),
+            },
+    );
+  }
+
+  @override
+  Type get runtimeType => ToJsonOptions;
+}