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Nested schemas requires all validations to pass #269

jomag opened this Issue Sep 1, 2015 · 3 comments


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jomag commented Sep 1, 2015

If the validation of a single field in a nested schema fails, then values of the entire nested schema are thrown away. Example:

import marshmallow as ma

class Child(ma. Schema):
    a = ma.fields.Integer()
    b = ma.fields.Integer()

class Parent(ma.Schema):
    x = ma.fields.Integer()
    y = ma.fields.Integer()
    z = ma.fields.Nested(Child)

p = Parent()

If I call p.load() with a dict that has 'x' set to a valid integer, and 'y' set to None, the returned data has one value, and the error list contains on error message for 'y'

But if I do the same thing with the child instance ('z') and set for example 'a' to None, and 'b' to a valid value, then the entire nested schema ('z') is absent from the data returned by p.load()

I'm trying to use marshmallow for saving settings to disk. I do not want the loading method to skip an entire nested object just because one of the values of it are invalid.

Any ideas?


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jomag commented Sep 2, 2015

I wrote a small test program:

import marshmallow as ma
from pprint import pprint

class SchemaA(ma.Schema):
    x = ma.fields.Integer()
    y = ma.fields.Integer()
    z = ma.fields.Integer()

class SchemaB(ma.Schema):
    w = ma.fields.Integer()
    n = ma.fields.Nested(SchemaA)

def test(schema_class, input_data):
    print('-' * 80)
    print("Input data:")

    sch = schema_class()
    data, errors = sch.load(input_data)

    print("Validated data:")

    print("Validation errors:")

test(SchemaA, { 'x': 50, 'y': 60, 'z': None })
test(SchemaB, { 'w': 90, 'n': { 'x': 90, 'y': 89, 'z': None} })
print('-' * 80)


Input data:
{'x': 50, 'y': 60, 'z': None}
Validated data:
{'x': 50, 'y': 60}
Validation errors:
{'z': [u'Field may not be null.']}
Input data:
{'n': {'x': 90, 'y': 89, 'z': None}, 'w': 90}
Validated data:
{'w': 90}
Validation errors:
{'n': {'z': [u'Field may not be null.']}}

As for the second test I would want the validated data to be:

{ 'w': 90, 'n': { 'x': 90, 'y': 89 } }

And the errors:

{ 'n': { 'z': [ u'Field may not be null' ] } }

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jomag commented Sep 2, 2015

The following patch fixes the problem, but I'm not familiar with the code base so it is a quite ugly hack ... It applies cleanly to tag 2.0.0b5.

diff --git a/marshmallow/ b/marshmallow/
index 706b28f..4ad51bd 100644
--- a/marshmallow/
+++ b/marshmallow/
@@ -39,6 +39,12 @@ class ValidationError(MarshmallowError):
         MarshmallowError.__init__(self, message)

+class NestedValidationError(ValidationError):
+    def __init__(self, message, value=None, field_names=None, fields=None):
+        super(NestedValidationError, self).__init__(message, field_names, fields)
+        self.value = value
 class RegistryError(NameError):
     """Raised when an invalid operation is performed on the serializer
     class registry.
diff --git a/marshmallow/ b/marshmallow/
index 0990f11..5f7a63a 100755
--- a/marshmallow/
+++ b/marshmallow/
@@ -13,7 +13,7 @@ from marshmallow import validate, utils, class_registry
 from marshmallow.base import FieldABC, SchemaABC
 from marshmallow.utils import missing as missing_
 from marshmallow.compat import text_type, basestring
-from marshmallow.exceptions import ValidationError
+from marshmallow.exceptions import ValidationError, NestedValidationError

 __all__ = [
@@ -385,7 +385,7 @@ class Nested(Field):

         data, errors = self.schema.load(value)
         if errors:
-            raise ValidationError(errors)
+            raise NestedValidationError(errors, data)
         return data

     def _validate_missing(self, value):
diff --git a/marshmallow/ b/marshmallow/
index 8bbb42d..b531a74 100644
--- a/marshmallow/
+++ b/marshmallow/
@@ -14,7 +14,7 @@ from marshmallow import utils
 from marshmallow.utils import missing
 from marshmallow.compat import text_type, iteritems
 from marshmallow.exceptions import (
-    ValidationError,
+    ValidationError, NestedValidationError

 __all__ = [
@@ -71,7 +71,10 @@ class ErrorStore(object):
                 errors[field_name] = err.messages
                 errors.setdefault(field_name, []).extend(err.messages)
-            value = missing
+            if isinstance(err, NestedValidationError):
+                value = err.value
+            else:
+                value = missing
         return value

 class Marshaller(ErrorStore):

@sloria sloria added this to the 2.0.0 (final) milestone Sep 6, 2015

@sloria sloria closed this in 02de91b Sep 11, 2015


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sloria commented Sep 11, 2015

This is now fixed. I used a similar solution to the one above, without adding a new Exception class. Thanks @jomag for the suggestion and your work on finding a solution!

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