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Dict(values=Nested()) doesn't collect complete validation errors #730

shabble opened this Issue Jan 29, 2018 · 1 comment


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shabble commented Jan 29, 2018

Using the new structured Dict support from #483 / #700, the error handling/collection logic seems unable to provide access to the original/detailed failures due to how it aggregates multiple errors.

  • marshmallow.version = '3.0.0b6'
  • Python 2.7.14

Simple test is something like:

from marshmallow import Schema, pprint, fields
from marshmallow.validate import OneOf

class InnerSchema(Schema):
    inner = fields.String(validate=OneOf(['a','b'], error='inner validation fail on {input}'))

class OuterSchema(Schema):
    outer = fields.Dict(values=fields.Nested(InnerSchema))

foo = {
    'outer': {
        'x': {'inner': 'a'},
foo2 = {
    'outer': {
        'x': {'inner': 'xxx'},

# This works (no validation failures)
outer_sch = OuterSchema()
ret = outer_sch.load(foo)
# >>> UnmarshalResult(data={'outer': {'x': {'inner': u'a'}}}, errors={})

# Fails to validate Inner.inner
outer_sch2 = OuterSchema()
ret2 = outer_sch.load(foo2)
# >>> UnmarshalResult(data={}, errors={'outer': {'x': [u'Invalid value: inner']}})
# Note: the custom error message on outer.x.inner is not present.

# validation + custom message is working as expected on the inner String field.
inner_sch = InnerSchema()
inner2 = inner_sch.load(foo2['outer']['x'])
# >>> UnmarshalResult(data={}, errors={'inner': ['inner validation fail on xxx']})

I don't think it's possible to extract the actual failure message ('inner validation fail on xxx) with any of hte existing error handling overrides, because it's getting dropped (I think) here:

(since e.messages is a dict but the loop is only taking its keys).

Not sure exactly what an appropriate result would be. Any access to the inner validation structures would be fine for what I need.


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lafrech commented Jan 29, 2018

If possible, we should have the same structure as what the List field generates, except it would have "keys" rather than "indexes".

From List:

errors.update({idx: e.messages})

Maybe errors[key] should be a dict rather than a list, with at most two keys: key for the list of key errors and value for the list of value errors.

errors[key] = {
    'key': [],
    'value': [],

We could do (untested):

                    key = keys[idx]
                    if key not in errors:  # Avoid this test by using a defaultdict?
                        errors[key] = {}
                    errors[key]['value'] = e.messages

and likewise for key errors.

To be closer to List, errors itself could be a list rather than a dict. But I don't see any benefit to this apart from having similar structures for both. And it makes sense that List has an error list and Dict an error dict.

@lafrech lafrech added this to the 3.0 milestone Feb 3, 2018

lafrech added a commit to Nobatek/marshmallow that referenced this issue Feb 7, 2018

lafrech added a commit to Nobatek/marshmallow that referenced this issue Mar 18, 2018

@sloria sloria closed this in #734 Mar 24, 2018

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