How to check if the json schema is valid without the data?

[kishaningithub]

I would like to check if a given json schema is valid as part of unit testing.

Is there a way to do just that without requiring data?

[Julian]

The check_schema classmethod should be what you need here.

[kishaningithub]

@Julian Thanks for the pointer :-) I am putting here a sample code in python3 for people who stumble upon this and are in a hurry to find out how to call that method

Sample code

Here i have deliberately put the type as <<INVALID TYPE>> to see what comes out in the exception

import json

from jsonschema.exceptions import SchemaError
from jsonschema.validators import validator_for

json_schema = json.loads("""
{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://example.com/product.schema.json",
  "title": "Product",
  "description": "A product from Acme's catalog",
  "type": "object",
  "properties": {
    "productId": {
      "description": "The unique identifier for a product",
      "type": "<<INVALID TYPE>>"
    }
  },
  "required": [ "productId" ]
}
""")


try:
    validator_for(json_schema).check_schema(json_schema)
    print("validation succeeded")
except SchemaError as e:
    print(f"validation failed {e}")

Result

validation failed '<<INVALID TYPE>>' is not valid under any of the given schemas

Failed validating 'anyOf' in metaschema['allOf'][1]['properties']['properties']['additionalProperties']['$dynamicRef']['allOf'][3]['properties']['type']:
    {'anyOf': [{'$ref': '#/$defs/simpleTypes'},
               {'items': {'$ref': '#/$defs/simpleTypes'},
                'minItems': 1,
                'type': 'array',
                'uniqueItems': True}]}

On schema['properties']['productId']['type']:
    '<<INVALID TYPE>>'

[kishaningithub]

@Julian Upon further analysis i figured this does not validate the "format". Is there a way to make that happen as well?

Code

Note that i have put the "format" field in the schema as <<INVALID FORMAT>>

import json

from jsonschema.exceptions import SchemaError
from jsonschema.validators import validator_for

json_schema = json.loads("""
{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://example.com/product.schema.json",
  "title": "Product",
  "description": "A product from Acme's catalog",
  "type": "object",
  "properties": {
    "productId": {
      "description": "The unique identifier for a product",
      "type": "string",
      "format": "<<INVALID FORMAT>>"
    }
  },
  "required": [ "productId" ]
}
""")


try:
    validator_for(json_schema).check_schema(json_schema)
    print("validation succeeded")
except SchemaError as e:
    print(f"validation failed {e}")

Output

validation succeeded

[redm123]

Same problem here. How can I validate wrong format identifier in a schema itself?

I tried adding a format checker (I used evolve(), not sure that is the correct way to do it. The documentation is a little confusing here..). But still it does not complain about wrong formats. Not sure, though, if a format checker is the right thing to use here in the first place? But what else?

import json
import jsonschema

schema_json = json.loads("""
{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "type": "object",
  "properties": {
    "foobar": {
      "type": "string",
      "format": "somerandomunknownformat"
    }
  },
  "required": [
    "foobar" 
  ]
}
""")

try:
    d4_validator = jsonschema.Draft4Validator({})
    d4_validator.evolve(format_checker=jsonschema.Draft4Validator.FORMAT_CHECKER)
    d4_validator.check_schema(schema_json)
    print("validation succeeded")
except jsonschema.exceptions.SchemaError as e:
    print(f"validation failed {e}")

[Gustutu]

I also need to validate a json schema, what is the prefered way to do it today ?

[Julian]

Making check_schema validate formats by default was done in v4.17.0 (even though the previous behavior was not strictly speaking incorrect according to the spec unfortunately.)