Now accepting as the required message anything that the ValidationErr…

…or constructor takes

docs/quickstart.rst

@@ -236,18 +236,23 @@ Required Fields
 
 You can make a field required by passing ``required=True``. An error will be stored if the the value is missing from the input to :meth:`Schema.load`.
 
-Alternatively, you can provide a custom error message by passing ``required='My custom message'`` (and the required validation will be enabled as if ``required=True``)
+Alternatively, you can provide a custom error message by passing ``required='My custom message'`` (and the required validation will be enabled when ``if required`` succeeds).
+Dictionaries or lists are also accepted as the custom error message, in case you want to provide more information with the error.
 
 .. code-block:: python
     :emphasize-lines: 2,6
 
     class UserSchema(Schema):
         name = fields.String(required=True)
         age = fields.Integer(required='Age is required.')
+        city = fields.String(required={'message': 'City required', 'code': 400})
         email = fields.Email()
 
     data, errors = UserSchema().load({'email': '[email protected]'})
-    errors  # {'name': ['Missing data for required field.'], 'age': ['Age is required.']}
+    errors
+    # {'name': ['Missing data for required field.'],
+    #  'age': ['Age is required.'],
+    #  'city': {'message': 'City required', 'code': 400}}
 
 Schema.validate
 +++++++++++++++

marshmallow/fields.py

@@ -324,9 +324,11 @@ class Field(FieldABC):
         its only parameter and returns a boolean.
         If it returns `False`, an :exc:`UnmarshallingError` is raised.
     :param required: Raise an :exc:`UnmarshallingError` if the field value
-        is not supplied during deserialization. If it is a string, this validation
-        will be enabled and the provided string will be used as the error message
-        instead of the built in one.
+        is not supplied during deserialization. If it is not a bool, this validation
+        will be enabled when `if required` succeeds, and the provided value will be
+        used as the message of the ValidationError instead of the built in one.
+        In this case, message can be anything that the ValidationError constructor
+        accepts (a string, list or dict)
     :param metadata: Extra arguments to be stored as metadata.
 
     .. versionchanged:: 1.0.0
@@ -459,8 +461,9 @@ def deserialize(self, value):
         def do_deserialization():
             if value is missing:
                 if hasattr(self, 'required') and self.required:
-                    message = (self.required if isinstance(self.required, basestring) else
-                               'Missing data for required field.')
+                    default_message = 'Missing data for required field.'
+                    message = (default_message if isinstance(self.required, bool) else
+                               self.required)
                     raise ValidationError(message)
             output = self._deserialize(value)
             self._validate(output)

tests/test_deserialization.py

@@ -7,7 +7,7 @@
 
 from marshmallow import fields, utils, Schema
 from marshmallow.exceptions import UnmarshallingError, ValidationError
-from marshmallow.compat import text_type, total_seconds
+from marshmallow.compat import text_type, total_seconds, basestring
 
 from tests.base import (
     assert_almost_equal,
@@ -1031,13 +1031,15 @@ class ColorSchema(Schema):
     assert data == {}
 
 
-def test_required_message_can_be_changed():
-    message = 'My custom required message'
-
+@pytest.mark.parametrize('message', ['My custom required message',
+                                     {'error': 'something', 'code': 400},
+                                     ['first error', 'second error']])
+def test_required_message_can_be_changed(message):
     class RequireSchema(Schema):
         age = fields.Integer(required=message)
 
     user_data = {"name": "Phil"}
     data, errs = RequireSchema().load(user_data)
-    assert message in errs['age']
+    expected = [message] if isinstance(message, basestring) else message
+    assert expected == errs['age']
     assert data == {}