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

问题

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 documents such that they are accessible at an HTTP URI. As such, all references are relative. All documents live in a local folder structure.

How can I make python-jsonschema understand to properly use my local file system to load referenced documents?

For instance, if I have a document with filename defs.json containing some definitions. And I try to load a different document which references it, like:

{
  "allOf": [
    {"$ref":"defs.json#/definitions/basic_event"},
    {
      "type": "object",
      "properties": {
        "action": {
          "type": "string",
          "enum": ["page_load"]
        }
      },
      "required": ["action"]
    }
  ]
}

I get an error RefResolutionError: <urlopen error [Errno 2] No such file or directory: '/defs.json'>

It may be important that I'm on a linux box.

(I'm writing this as a Q&A because I had a hard time figuring this out and observed other folks having trouble too.)

回答1:

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)

回答2:

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:

Create the base schema:

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

Create the extension schema

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

Create your JSON file you want to test against the schema

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

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)

来源：https://stackoverflow.com/questions/53968770/how-to-set-up-local-file-references-in-python-jsonschema-document

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python

json

jsonschema

python-jsonschema