Fix flask example and add schema_example

Demonstrates an implementation of use_schema

examples/flask_example.py

@@ -61,7 +61,7 @@ def dateadd(value, addend, unit):
     return jsonify({'result': result.isoformat()})
 
 # Return validation errors as JSON
-@app.errorhandler(400)
+@app.errorhandler(422)
 def handle_validation_error(err):
     exc = err.data['exc']
     return jsonify({'errors': exc.messages}), 400

examples/schema_example.py

@@ -0,0 +1,119 @@
+"""Example implementation of using a marshmallow Schema for both request input
+and output with a `use_schema` decorator.
+Run the app:
+
+    $ python examples/schema_example.py
+
+Try the following with httpie (a cURL-like utility, http://httpie.org):
+
+    $ pip install httpie
+    $ http GET :5001/users/
+    $ http GET :5001/users/42
+    $ http POST :5001/users/ usename=brian first_name=Brian last_name=May
+    $ http PATCH :5001/users/42 username=freddie
+"""
+import functools
+from flask import Flask, request, jsonify
+import random
+
+from marshmallow import Schema, fields, post_dump
+from webargs.flaskparser import parser
+
+app = Flask(__name__)
+
+##### Fake database and models #####
+
+class Model:
+    def __init__(self, **kwargs):
+        self.__dict__.update(kwargs)
+
+    def update(self, **kwargs):
+        self.__dict__.update(kwargs)
+
+    @classmethod
+    def insert(cls, db, **kwargs):
+        collection = db[cls.collection]
+        new_id = None
+        if 'id' in kwargs:  # for setting up fixtures
+            new_id = kwargs.pop('id')
+        else:  # find a new id
+            found_id = False
+            while not found_id:
+                new_id = random.randint(1, 9999)
+                if new_id not in collection:
+                    found_id = True
+        new_record = cls(id=new_id, **kwargs)
+        collection[new_id] = new_record
+        return new_record
+
+class User(Model):
+    collection = 'users'
+
+db = {'users': {}}
+
+
+##### use_schema #####
+
+def use_schema(schema, list_view=False, locations=None):
+    """Decorator for using a marshmallow schema for
+        (1) parsing a request's input and
+        (2) serializing its output to a JSON response.
+    """
+    def decorator(func):
+        @functools.wraps(func)
+        def wrapped(*args, **kwargs):
+            use_args_wrapper = parser.use_args(schema, locations=locations)
+            # Function wrapped with use_args
+            func_with_args = use_args_wrapper(func)
+            ret = func_with_args(*args, **kwargs)
+            # Serialize and jsonify the return value
+            return jsonify(schema.dump(ret, many=list_view).data)
+        return wrapped
+    return decorator
+
+##### Schemas #####
+
+class UserSchema(Schema):
+    id = fields.Int(dump_only=True)
+    username = fields.Str()
+    first_name = fields.Str()
+    last_name = fields.Str()
+
+    class Meta:
+        strict = True
+
+    @post_dump(pass_many=True)
+    def wrap_with_envelope(self, data, many):
+        return {'data': data}
+
+
+##### Routes #####
+
+@app.route('/users/', methods=['GET', 'POST'])
+@use_schema(UserSchema(), list_view=True)
+def user_list(reqargs):
+    users = db['users'].values()
+    if request.method == 'POST':
+        User.insert(db=db, **reqargs)
+    return users
+
+
+@app.route('/users/<int:user_id>', methods=['GET', 'PATCH'])
+@use_schema(UserSchema())
+def user_detail(reqargs, user_id):
+    user = db['users'].get(user_id)
+    if not user:
+        return jsonify({'message': 'User not found'}), 404
+    if request.method == 'PATCH' and reqargs:
+        user.update(**reqargs)
+    return user
+
+# Return validation errors as JSON
+@app.errorhandler(422)
+def handle_validation_error(err):
+    exc = err.data['exc']
+    return jsonify({'errors': exc.messages}), 422
+
+if __name__ == "__main__":
+    User.insert(db=db, id=42, username='fred', first_name='Freddie', last_name='Mercury')
+    app.run(port=5001, debug=True)