Add helper class for reporting multiple errors

marshmallow/utils.py

@@ -15,6 +15,7 @@
 from pprint import pprint as py_pprint
 
 from marshmallow.compat import OrderedDict, binary_type, iteritems, text_type
+from marshmallow.exceptions import ValidationError
 
 
 # Key used for schema-level validation errors
@@ -407,3 +408,66 @@ def merge_errors(errors1, errors2):
             )
         else:
             return [text_type(errors1), text_type(errors2)]
+
+
+class ValidationErrorBuilder(object):
+    """Helper class to report multiple errors.
+
+    Example:
+
+        @marshmallow.validates_schema
+        def validate_all(self, data):
+            builder = marshmallow.utils.ValidationErrorBuilder()
+            if data['foo']['bar'] >= data['baz']['bam']:
+                builder.add_error('foo/bar', 'Should be less than bam')
+            if data['foo']['quux'] >= data['baz']['bam']:
+                builder.add_fields('foo/quux', 'Should be less than bam')
+            ...
+            builder.raise_errors()
+    """
+
+    def __init__(self):
+        self.errors = {}
+
+    def _make_error(self, path, error):
+        parts = path.split('.', 1)
+
+        if len(parts) == 1:
+            return {path: error}
+        else:
+            return {parts[0]: self._make_error(parts[1], error)}
+
+    def add_error(self, path, error):
+        """Add error message for given field path.
+
+        Example:
+
+            builder = ValidationErrorBuilder()
+            builder.add_error('foo.bar.baz', 'Some error')
+            print builder.errors
+            # => {'foo': {'bar': {'baz': 'Some error'}}}
+
+        :param str path: '/'-separated list of field names
+        :param str error: Error message
+        """
+        self.errors = merge_errors(self.errors, self._make_error(path, error))
+
+    def merge_errors(self, errors):
+        """Add errors in dict format.
+
+        Example:
+
+            builder = ValidationErrorBuilder()
+            builder.add_errors({'foo': {'bar': 'Error 1'}})
+            builder.add_errors({'foo': {'baz': 'Error 2'}, 'bam': 'Error 3'})
+            print builder.errors
+            # => {'foo': {'bar': 'Error 1', 'baz': 'Error 2'}, 'bam': 'Error 3'}
+
+        :param str, list or dict errors: Errors to merge
+        """
+        self.errors = merge_errors(self.errors, errors)
+
+    def raise_errors(self):
+        """Raise ValidationError if errors are not empty; do nothing otherwise."""
+        if self.errors:
+            raise ValidationError(self.errors)

tests/test_utils.py

@@ -5,6 +5,7 @@
 
 import pytest
 
+from marshmallow.exceptions import ValidationError
 from marshmallow import utils
 from tests.base import (
     assert_datetime_equal,
@@ -296,3 +297,54 @@ def test_deep_merging_dicts(self):
         assert {'field1': {'field2': ['error1', 'error2']}} == \
             utils.merge_errors({'field1': {'field2': 'error1'}},
                                {'field1': {'field2': 'error2'}})
+
+
+class TestValidationErrorBuilder:
+
+    def test_empty_errors(self):
+        builder = utils.ValidationErrorBuilder()
+        assert {} == builder.errors
+
+    def test_adding_field_error(self):
+        builder = utils.ValidationErrorBuilder()
+        builder.add_error('foo', 'error 1')
+        assert {'foo': 'error 1'} == builder.errors
+
+    def test_adding_multiple_errors(self):
+        builder = utils.ValidationErrorBuilder()
+        builder.add_error('foo', 'error 1')
+        builder.add_error('bar', 'error 2')
+        builder.add_error('bam', 'error 3')
+        assert {'foo': 'error 1', 'bar': 'error 2', 'bam': 'error 3'} == \
+            builder.errors
+
+    def test_adding_nested_errors(self):
+        builder = utils.ValidationErrorBuilder()
+        builder.add_error('foo.bar', 'error 1')
+        assert {'foo': {'bar': 'error 1'}} == builder.errors
+
+    def test_adding_multiple_nested_errors(self):
+        builder = utils.ValidationErrorBuilder()
+        builder.add_error('foo.bar', 'error 1')
+        builder.add_error('foo.baz.bam', 'error 2')
+        builder.add_error('quux', 'error 3')
+        assert {'foo': {'bar': 'error 1', 'baz': {'bam': 'error 2'}},
+                'quux': 'error 3'} == builder.errors
+
+    def test_adding_merging_errors(self):
+        builder = utils.ValidationErrorBuilder()
+        builder.merge_errors({'foo': {'bar': 'error 1'}})
+        builder.merge_errors({'foo': {'baz': 'error 2'}})
+        assert {'foo': {'bar': 'error 1', 'baz': 'error 2'}} == builder.errors
+
+    def test_raise_errors_on_empty_builder_does_nothing(self):
+        builder = utils.ValidationErrorBuilder()
+        builder.raise_errors()
+
+    def test_raise_errors_on_non_empty_builder_raises_ValidationError(self):
+        builder = utils.ValidationErrorBuilder()
+        builder.add_error('foo', 'error 1')
+        with pytest.raises(ValidationError) as excinfo:
+            builder.raise_errors()
+
+        assert excinfo.value.messages == builder.errors