How to set up local file references in python-jsonschema document?

Question

I have a set of jsonschema compliant documents. Some documents contain references to other documents (via the $ref attribute). I do not wish to host these docum

Answer 1

Following up on the answer @chris-w provided, I wanted to do this same thing with jsonschema 3.2.0 but his answer didn't quite cover it I hope this answer helps those who are still coming to this question for help but are using a more recent version of the package.

To extend a JSON schema using the library, do the following:

1. Create the base schema:

base.schema.json
{
  "$id": "base.schema.json",
  "type": "object",
  "properties": {
    "prop": {
      "type": "string"
    }
  },
  "required": ["prop"]
}

2. Create the extension schema

extend.schema.json
{
  "allOf": [
    {"$ref": "base.schema.json"},
    {
      "properties": {
        "extra": {
          "type": "boolean"
        }
      },
      "required": ["extra"]
    }
  ]
}

3. Create your JSON file you want to test against the schema

data.json
{
  "prop": "This is the property",
  "extra": true
}

4. Create your RefResolver and Validator for the base Schema and use it to check the data

#Set up schema, resolver, and validator on the base schema
baseSchema = json.loads(baseSchemaJSON) # Create a schema dictionary from the base JSON file
relativeSchema = json.loads(relativeJSON) # Create a schema dictionary from the relative JSON file
resolver = RefResolver.from_schema(baseSchema) # Creates your resolver, uses the "$id" element
validator = Draft7Validator(relativeSchema, resolver=resolver) # Create a validator against the extended schema (but resolving to the base schema!)

# Check validation!
data = json.loads(dataJSON) # Create a dictionary from the data JSON file
validator.validate(data)

You may need to make a few adjustments to the above entries, such as not using the Draft7Validator. This should work for single-level references (children extending a base), you will need to be careful with your schemas and how you set up the RefResolver and Validator objects.

P.S. Here is a snipped that exercises the above. Try modifying the data string to remove one of the required attributes:

import json

from jsonschema import RefResolver, Draft7Validator

base = """
{
  "$id": "base.schema.json",
  "type": "object",
  "properties": {
    "prop": {
      "type": "string"
    }
  },
  "required": ["prop"]
}
"""

extend = """
{
  "allOf": [
    {"$ref": "base.schema.json"},
    {
      "properties": {
        "extra": {
          "type": "boolean"
        }
      },
      "required": ["extra"]
    }
  ]
}
"""

data = """
{
"prop": "This is the property string",
"extra": true
}
"""

schema = json.loads(base)
extendedSchema = json.loads(extend)
resolver = RefResolver.from_schema(schema)
validator = Draft7Validator(extendedSchema, resolver=resolver)

jsonData = json.loads(data)
validator.validate(jsonData)

Answer 2

You must build a custom jsonschema.RefResolver for each schema which uses a relative reference and ensure that your resolver knows where on the filesystem the given schema lives.

Such as...

import os
import json
from jsonschema import Draft4Validator, RefResolver # We prefer Draft7, but jsonschema 3.0 is still in alpha as of this writing 


abs_path_to_schema = '/path/to/schema-doc-foobar.json'
with open(abs_path_to_schema, 'r') as fp:
  schema = json.load(fp)

resolver = RefResolver(
  # The key part is here where we build a custom RefResolver 
  # and tell it where *this* schema lives in the filesystem
  # Note that `file:` is for unix systems
  schema_path='file:{}'.format(abs_path_to_schema),
  schema=schema
)
Draft4Validator.check_schema(schema) # Unnecessary but a good idea
validator = Draft4Validator(schema, resolver=resolver, format_checker=None)

# Then you can...
data_to_validate = `{...}`
validator.validate(data_to_validate)

Answer 3

EDIT

Fixed a wrong reference ($ref) to base schema. Updated the example to use the one from the docs: https://json-schema.org/understanding-json-schema/structuring.html

This is just another version of @Daniel's answer -- which was the one correct for me. Basically, I decided to define the $schema in a base schema. Which then release the other schemas and makes for a clear call when instantiating the resolver.

• The fact that RefResolver.from_schema() gets (1) some schema and also (2) a schema-store was not very clear to me whether the order and which "some" schema were relevant here. And so the structure you see below.

I have the following:

base.schema.json:

{
  "$schema": "http://json-schema.org/draft-07/schema#"
}

definitions.schema.json:

{
  "type": "object",
  "properties": {
    "street_address": { "type": "string" },
    "city":           { "type": "string" },
    "state":          { "type": "string" }
  },
  "required": ["street_address", "city", "state"]
}

address.schema.json:

{
  "type": "object",

  "properties": {
    "billing_address": { "$ref": "definitions.schema.json#" },
    "shipping_address": { "$ref": "definitions.schema.json#" }
  }
}

I like this setup for two reasons:

1. Is a cleaner call on RefResolver.from_schema():

   base = json.loads(open('base.schema.json').read())
   definitions = json.loads(open('definitions.schema.json').read())
   schema = json.loads(open('address.schema.json').read())
   
   schema_store = {
     base.get('$id','base.schema.json') : base,
     definitions.get('$id','definitions.schema.json') : definitions,
     schema.get('$id','address.schema.json') : schema,
   }
   
   resolver = RefResolver.from_schema(base, store=schema_store)
   

2. Then I profit from the handy tool the library provides give you the best validator_for your schema (according to your $schema key):

   Validator = validator_for(base)
   

3. And then just put them together to instantiate validator:

   validator = Validator(schema, resolver=resolver)
   

Finally, you validate your data:

data = {
  "shipping_address": {
    "street_address": "1600 Pennsylvania Avenue NW",
    "city": "Washington",
    "state": "DC"   
  },
  "billing_address": {
    "street_address": "1st Street SE",
    "city": "Washington",
    "state": 32
  }
}

• This one will crash since "state": 32:

>>> validator.validate(data)

ValidationError: 32 is not of type 'string'

Failed validating 'type' in schema['properties']['billing_address']['properties']['state']:
    {'type': 'string'}

On instance['billing_address']['state']:
    32

Change that to "DC", and will validate.

Answer 4

I had the hardest time figuring out how to do resolve against a set of schemas that $ref each other (I am new to JSON Schemas). It turns out the key is to create the RefResolver with a store that is a dict which maps from url to schema. Building on @devin-p's answer:

import json

from jsonschema import RefResolver, Draft7Validator

base = """
{
  "$id": "base.schema.json",
  "type": "object",
  "properties": {
    "prop": {
      "type": "string"
    }
  },
  "required": ["prop"]
}
"""

extend = """
{  
  "$id": "extend.schema.json",
  "allOf": [
    {"$ref": "base.schema.json#"},
    {
      "properties": {
        "extra": {
          "type": "boolean"
        }
      },
    "required": ["extra"]
    }
  ]
}
"""

extend_extend = """
{
  "$id": "extend_extend.schema.json",
  "allOf": [
    {"$ref": "extend.schema.json#"},
    {
      "properties": {
        "extra2": {
          "type": "boolean"
        }
      },
    "required": ["extra2"]
    }
  ]
}
"""

data = """
{
"prop": "This is the property string",
"extra": true,
"extra2": false
}
"""

schema = json.loads(base)
extendedSchema = json.loads(extend)
extendedExtendSchema = json.loads(extend_extend)
schema_store = {
    schema['$id'] : schema,
    extendedSchema['$id'] : extendedSchema,
    extendedExtendSchema['$id'] : extendedExtendSchema,
}


resolver = RefResolver.from_schema(schema, store=schema_store)
validator = Draft7Validator(extendedExtendSchema, resolver=resolver)

jsonData = json.loads(data)
validator.validate(jsonData)

The above was built with jsonschema==3.2.0.

Answer 5

My approach is to preload all schema fragments to RefResolver cache. I created a gist that illustrates this: https://gist.github.com/mrtj/d59812a981da17fbaa67b7de98ac3d4b