django postgresql json field schema validation - json

Question

I have a django model with a JSONField (django.contrib.postgres.fields.JSONField)
Is there any way that I can validate model data against a json schema file?
(pre-save)
Something like my_field = JSONField(schema_file=my_schema_file)

Answer 1

I wrote a custom validator using jsonschema in order to do this.
project/validators.py
import django
from django.core.validators import BaseValidator
import jsonschema
class JSONSchemaValidator(BaseValidator):
def compare(self, value, schema):
try:
jsonschema.validate(value, schema)
except jsonschema.exceptions.ValidationError:
raise django.core.exceptions.ValidationError(
'%(value)s failed JSON schema check', params={'value': value}
)
project/app/models.py
from django.db import models
from project.validators import JSONSchemaValidator
MY_JSON_FIELD_SCHEMA = {
'schema': 'http://json-schema.org/draft-07/schema#',
'type': 'object',
'properties': {
'my_key': {
'type': 'string'
}
},
'required': ['my_key']
}
class MyModel(models.Model):
my_json_field = models.JSONField(
default=dict,
validators=[JSONSchemaValidator(limit_value=MY_JSON_FIELD_SCHEMA)]
)

Answer 2

That's what the Model.clean() method is for (see docs). Example:
class MyData(models.Model):
some_json = JSONField()
...
def clean(self):
if not is_my_schema(self.some_json):
raise ValidationError('Invalid schema.')

Answer 3

you could use cerberus to validate your data against a schema
from cerberus import Validator
schema = {'name': {'type': 'string'}}
v = Validator(schema)
data = {'name': 'john doe'}
v.validate(data) # returns "True" (if passed)
v.errors # this would return the error dict (or on empty dict in case of no errors)
it's pretty straightforward to use (also due to it's good documentation -> validation rules: http://docs.python-cerberus.org/en/stable/validation-rules.html)

Answer 4

I wrote a custom JSONField that extends models.JSONField and validates attribute's value by using jsonschema (Django 3.1, Python 3.7).
I didn't use the validators parameter for one reason: I want to let users define the schema dynamically.So I use a schema parameter, that should be:
None (by default): the field will behave like its parent class (no JSON schema validation support).
A dict object. This option is suitable for a small schema definition (for example: {"type": "string"});
A str object that describes a path to the file where the schema code is contained. This option is suitable for a big schema definition (to preserve the beauty of the model class definition code). For searching I use all enabled finders: django.contrib.staticfiles.finders.find().
A function that takes a model instance as an argument and returns a schema as dict object. So you can build a schema based on the state of the given model instance. The function will be called every time when the validate() is called.
myapp/models/fields.py
import json
from jsonschema import validators as json_validators
from jsonschema import exceptions as json_exceptions
from django.contrib.staticfiles import finders
from django.core import checks, exceptions
from django.db import models
from django.utils.functional import cached_property
class SchemaMode:
STATIC = 'static'
DYNAMIC = 'dynamic'
class JSONField(models.JSONField):
"""
A models.JSONField subclass that supports the JSON schema validation.
"""
def __init__(self, *args, schema=None, **kwargs):
if schema is not None:
if not(isinstance(schema, (bool, dict, str)) or callable(schema)):
raise ValueError('The "schema" parameter must be bool, dict, str, or callable object.')
self.validate = self._validate
else:
self.__dict__['schema_mode'] = False
self.schema = schema
super().__init__(*args, **kwargs)
def check(self, **kwargs):
errors = super().check(**kwargs)
if self.schema_mode == SchemaMode.STATIC:
errors.extend(self._check_static_schema(**kwargs))
return errors
def _check_static_schema(self, **kwargs):
try:
schema = self.get_schema()
except (TypeError, OSError):
return [
checks.Error(
f"The file '{self.schema}' cannot be found.",
hint="Make sure that 'STATICFILES_DIRS' and 'STATICFILES_FINDERS' settings "
"are configured correctly.",
obj=self,
id='myapp.E001',
)
]
except json.JSONDecodeError:
return [
checks.Error(
f"The file '{self.schema}' contains an invalid JSON data.",
obj=self,
id='myapp.E002'
)
]
validator_cls = json_validators.validator_for(schema)
try:
validator_cls.check_schema(schema)
except json_exceptions.SchemaError:
return [
checks.Error(
f"{schema} must be a valid JSON Schema.",
obj=self,
id='myapp.E003'
)
]
else:
return []
def deconstruct(self):
name, path, args, kwargs = super().deconstruct()
if self.schema is not None:
kwargs['schema'] = self.schema
return name, path, args, kwargs
#cached_property
def schema_mode(self):
if callable(self.schema):
return SchemaMode.DYNAMIC
return SchemaMode.STATIC
#cached_property
def _get_schema(self):
if callable(self.schema):
return self.schema
elif isinstance(self.schema, str):
with open(finders.find(self.schema)) as fp:
schema = json.load(fp)
else:
schema = self.schema
return lambda obj: schema
def get_schema(self, obj=None):
"""
Return schema data for this field.
"""
return self._get_schema(obj)
def _validate(self, value, model_instance):
super(models.JSONField, self).validate(value, model_instance)
schema = self.get_schema(model_instance)
try:
json_validators.validate(value, schema)
except json_exceptions.ValidationError as e:
raise exceptions.ValidationError(e.message, code='invalid')
Usage:
myapp/models/__init__.py
def schema(instance):
schema = {}
# Here is your code that uses the other
# instance's fields to create a schema.
return schema
class JSONSchemaModel(models.Model):
dynamic = JSONField(schema=schema, default=dict)
from_dict = JSONField(schema={'type': 'object'}, default=dict)
# A static file: myapp/static/myapp/schema.json
from_file = JSONField(schema='myapp/schema.json', default=dict)

Answer 5

Another solution using jsonschema for simple cases.
class JSONValidatedField(models.JSONField):
def __init__(self, *args, **kwargs):
self.props = kwargs.pop('props')
self.required_props = kwargs.pop('required_props', [])
super().__init__(*args, **kwargs)
def validate(self, value, model_instance):
try:
jsonschema.validate(
value, {
'schema': 'http://json-schema.org/draft-07/schema#',
'type': 'object',
'properties': self.props,
'required': self.required_props
}
)
except jsonschema.exceptions.ValidationError:
raise ValidationError(
f'Value "{value}" failed schema validation.')
class SomeModel(models.Model):
my_json_field = JSONValidatedField(
props={
'foo': {'type': 'string'},
'bar': {'type': 'integer'}
},
required_props=['foo'])