diff --git a/modules/openapi-generator/src/main/resources/dart2/class.mustache b/modules/openapi-generator/src/main/resources/dart2/class.mustache
index a7ddbb4ae17..4e6bcfcfd08 100644
--- a/modules/openapi-generator/src/main/resources/dart2/class.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/class.mustache
@@ -107,6 +107,12 @@ class {{classname}} {
     {{/complexType}}
   {{/isDate}}
   {{/isDateTime}}
+    {{#required}}
+        {{^isNullable}}
+    if ({{name}} == null)
+      throw ArgumentError("$json has no {{name}} field which is required for {{classname}}");
+        {{/isNullable}}
+    {{/required}}
   {{/vars}}
   }
 
diff --git a/modules/openapi-generator/src/main/resources/dart2/class_oneof.mustache b/modules/openapi-generator/src/main/resources/dart2/class_oneof.mustache
index cc944f11263..25fd98563fa 100644
--- a/modules/openapi-generator/src/main/resources/dart2/class_oneof.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/class_oneof.mustache
@@ -1,24 +1,36 @@
 class {{classname}} {
-  dynamic instance;
+  /// Can be {{#oneOf}}[{{{.}}}], {{/oneOf}}
+  dynamic _instance;
 
   // default constructor
-  {{classname}}({
-  });
+  {{classname}}();
+
+  set instance(dynamic instance) {
+    if (!(instance == null{{#oneOf}} || instance is {{{.}}}{{/oneOf}}))
+      throw ArgumentError("${instance.runtimeType} is not a valid type for {{classname}}");
+    _instance = instance;
+  }
+
+  dynamic get instance => _instance;
 
   @override
   String toString() {
-    // TODO
+    return _instance.toString();
   }
 
   {{classname}}.fromJson(Map<String, dynamic> json) {
-    // TODO
-    // loop through models/primitive types defined in {{#oneOf}} {{{.}}} {{/oneOf}}
-    // and make sure the payload `json` deserializes to one and only one schema defined in oneOf
+    if (json == null) return;
+    // TODO primitives, lists, maps
+    {{#oneOf}}
+    try {
+      _instance = {{{.}}}.fromJson(json);
+    } on ArgumentError {
+    }
+    {{/oneOf}}
   }
 
   Map<String, dynamic> toJson() {
-    // TOOD there should be a class member/property called "instance"
-    // which is dynamic type and it stores the actual instance of the schema defined in oneOf
-    // if oneOf is [Dog, Cat], then the instance can store either an instance of Dog or Cat
+    // TODO primitives, lists, maps
+    return _instance.toJson();
   }
 }
diff --git a/samples/client/petstore/dart2/petstore_client_lib/lib/model/one_of_test.dart b/samples/client/petstore/dart2/petstore_client_lib/lib/model/one_of_test.dart
index ff8c884f4fe..3a30c1f52d2 100644
--- a/samples/client/petstore/dart2/petstore_client_lib/lib/model/one_of_test.dart
+++ b/samples/client/petstore/dart2/petstore_client_lib/lib/model/one_of_test.dart
@@ -1,27 +1,41 @@
 part of openapi.api;
 
 class OneOfTest {
-  dynamic instance;
+  /// Can be [Pet], [User], 
+  dynamic _instance;
 
   // default constructor
-  OneOfTest({
-  });
+  OneOfTest();
+
+  set instance(dynamic instance) {
+    if (!(instance == null || instance is Pet || instance is User))
+      throw ArgumentError("${instance.runtimeType} is not a valid type for OneOfTest");
+    _instance = instance;
+  }
+
+  dynamic get instance => _instance;
 
   @override
   String toString() {
-    // TODO
+    return _instance.toString();
   }
 
   OneOfTest.fromJson(Map<String, dynamic> json) {
-    // TODO
-    // loop through models/primitive types defined in  Pet  User 
-    // and make sure the payload `json` deserializes to one and only one schema defined in oneOf
+    if (json == null) return;
+    // TODO primitives, lists, maps
+    try {
+      _instance = Pet.fromJson(json);
+    } on ArgumentError {
+    }
+    try {
+      _instance = User.fromJson(json);
+    } on ArgumentError {
+    }
   }
 
   Map<String, dynamic> toJson() {
-    // TOOD there should be a class member/property called "instance"
-    // which is dynamic type and it stores the actual instance of the schema defined in oneOf
-    // if oneOf is [Dog, Cat], then the instance can store either an instance of Dog or Cat
+    // TODO primitives, lists, maps
+    return _instance.toJson();
   }
 }
 
diff --git a/samples/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart b/samples/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart
index b6ba8476356..5e94a8e387b 100644
--- a/samples/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart
+++ b/samples/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart
@@ -35,9 +35,13 @@ class Pet {
       null :
       Category.fromJson(json['category']);
     name = json['name'];
+    if (name == null)
+      throw ArgumentError("$json has no name field which is required for Pet");
     photoUrls = (json['photoUrls'] == null) ?
       null :
       (json['photoUrls'] as List).cast<String>();
+    if (photoUrls == null)
+      throw ArgumentError("$json has no photoUrls field which is required for Pet");
     tags = (json['tags'] == null) ?
       null :
       Tag.listFromJson(json['tags']);