fix: README.md dataclass payload option

Author: Vlad

README.md

@@ -7,6 +7,7 @@ Object-oriented rest framework based on starlette, marshmallow and apispec.
 * [Starlette] 0.12.0+
 * [Marshmallow] 3.0.0rc8+
 * [APISpec] 2.0.2+
+* [python-multipart] 0.0.5+
 
 ## Installation
 
@@ -17,32 +18,49 @@ $ pip install star_resty
 ## Example
 
 ```python
-from marshmallow import Schema, fields, ValidationError
+from marshmallow import Schema, fields, ValidationError, post_load
 from starlette.applications import Starlette
 from starlette.datastructures import UploadFile
 from starlette.responses import JSONResponse
 
-from star_resty import Method, Operation, endpoint, json_payload, form_payload, query, setup_spec
+from dataclasses import dataclass
 
+from star_resty import Method, Operation, endpoint, json_schema, json_payload, form_payload, query, setup_spec
+from typing import Optional
 
 class EchoInput(Schema):
     a = fields.Int()
 
 
-# Json Payload
+# Json Payload (by schema)
 class JsonPayloadSchema(Schema):
     a = fields.Int(required=True)
     s = fields.String()
 
 
+# Json Payload (by dataclass)
+@dataclass
+class Payload:
+    a: int
+    s: Optional[str] = None
+
+class JsonPayloadDataclass(Schema):
+    a=fields.Int(required=True)
+    s=fields.Str()
+
+    @post_load
+    def create_payload(self, data, **kwargs):
+        return Payload(**data)
+
+
 # Form Payload
 class FormFile(fields.Field):
     def _validate(self, value):
         if not isinstance(value, UploadFile):
             raise ValidationError('Not a file')
 
 
-class FormSchema(Schema):
+class FormPayload(Schema):
     id = fields.Int(required=True)
     file = FormFile()
 
@@ -65,20 +83,29 @@ class Echo(Method):
         return query_params
 
 
-@app.route('/post', methods=['POST'])
+@app.route('/post/schema', methods=['POST'])
 @endpoint
-class Post(Method):
-    meta = Operation(tag='default', description='post json')
+class PostSchema(Method):
+    meta = Operation(tag='default', description='post json (by schema)')
 
     async def execute(self, item: json_payload(JsonPayloadSchema)):
         return {'a': item.get('a') * 2, 's': item.get('s')}
 
+
+@app.route('/post/dataclass', methods=['POST'])
+@endpoint
+class PostDataclass(Method):
+    meta = Operation(tag='default', description='post json (by dataclass)')
+
+    async def execute(self, item: json_schema(JsonPayloadDataclass, Payload)):
+        return {'a': item.a * 3, 's': item.s}
+
 @app.route('/form', methods=['POST'])
 @endpoint
 class PostForm(Method):
     meta = Operation(tag='default', description='post form')
 
-    async def execute(self, form_data: form_payload(FormSchema)):
+    async def execute(self, form_data: form_payload(FormPayload)):
         file_name = form_data.get('file').filename
         id = form_data.get('id')
         return {'message': f"file {file_name} with id {id} received"}