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.. _schema_validation:
Schema-level validation
=======================
You can register schema-level validation functions for a :class:`Schema` using the `marshmallow.validates_schema <marshmallow.decorators.validates_schema>` decorator. By default, schema-level validation errors will be stored on the ``_schema`` key of the errors dictionary.
.. code-block:: python
from marshmallow import Schema, fields, validates_schema, ValidationError
class NumberSchema(Schema):
field_a = fields.Integer()
field_b = fields.Integer()
@validates_schema
def validate_numbers(self, data, **kwargs):
if data["field_b"] >= data["field_a"]:
raise ValidationError("field_a must be greater than field_b")
schema = NumberSchema()
try:
schema.load({"field_a": 1, "field_b": 2})
except ValidationError as err:
err.messages["_schema"]
# => ["field_a must be greater than field_b"]
Storing errors on specific fields
---------------------------------
It is possible to report errors on fields and subfields using a `dict`.
When multiple schema-leval validator return errors, the error structures are merged together in the :exc:`ValidationError <marshmallow.exceptions.ValidationError>` raised at the end of the validation.
.. code-block:: python
from marshmallow import Schema, fields, validates_schema, ValidationError
class NumberSchema(Schema):
field_a = fields.Integer()
field_b = fields.Integer()
field_c = fields.Integer()
field_d = fields.Integer()
@validates_schema
def validate_lower_bound(self, data, **kwargs):
errors = {}
if data["field_b"] <= data["field_a"]:
errors["field_b"] = ["field_b must be greater than field_a"]
if data["field_c"] <= data["field_a"]:
errors["field_c"] = ["field_c must be greater than field_a"]
if errors:
raise ValidationError(errors)
@validates_schema
def validate_upper_bound(self, data, **kwargs):
errors = {}
if data["field_b"] >= data["field_d"]:
errors["field_b"] = ["field_b must be lower than field_d"]
if data["field_c"] >= data["field_d"]:
errors["field_c"] = ["field_c must be lower than field_d"]
if errors:
raise ValidationError(errors)
schema = NumberSchema()
try:
schema.load({"field_a": 3, "field_b": 2, "field_c": 1, "field_d": 0})
except ValidationError as err:
err.messages
# => {
# 'field_b': [
# 'field_b must be greater than field_a',
# 'field_b must be lower than field_d'
# ],
# 'field_c': [
# 'field_c must be greater than field_a',
# 'field_c must be lower than field_d'
# ]
# }
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