python-validate-json-schema

Validate JSON Schema using Python

This is a helper project for JSON Schema validation in Python, which uses Jsonschema the most complete and compliant JSON Schema validator.

Aim of the application

• Validate the necessary fields present in JSON file
• Validate JSON Field type. We need data of a JSON filed in a type that we want. For example, we want all numeric fields in the number format instead of number encoded in a string format like this Marks: "75" so we can use it directly instead of checking and converting it every time.
• To learn the implementation of Jsonschema in python.
• To implement,JSON Conversion to Python Object using json.load or json.loads methods.

JSON Schema

JSON Schema is a specification for JSON based format for defining the structure of JSON data. It was written under IETF draft which expired in 2011. JSON Schema.

• Describes your existing data format.
• Clear, human- and machine-readable documentation.
• Complete structural validation, useful for automated testing.
• Complete structural validation, validating client-submitted data.

Currently the most complete and compliant JSON Schema validator available for python is Jsonschema.

Given below is a basic JSON schema, which covers a basic user details.

{
   "$schema": "http://json-schema.org/draft-04/schema#",
   "title": "User",
   "description": "A user request json",
   "type": "object",
   "properties": {
      "id": {
         "description": "The unique identifier for a user",
         "type": "integer"
      },
      "name": {
         "description": "Name of the user",
         "type": "string"
      },
      "contact_number": {
         "type": "number",
      }
   },
   "required": ["id", "name", "contact_number"]
}

jsonschema is an implementation of JSON Schema for Python. Using jsonschema, we can create a schema of our choice, so every time we can validate the JSON document against this schema, if it passed, we could say that the JSON document is valid.

Keyword	Description
$schema	The $schema keyword states that this schema is written according to the draft v4 specification.
title	You will use this to give a title to your schema.
description	A little description of the schema.
type	The type keyword defines the first constraint on our JSON data: it has to be a JSON Object.
properties	Defines various keys and their value types, minimum and maximum values to be used in JSON file.
required	This keeps a list of required properties.
minimum	This is the constraint to be put on the value and represents minimum acceptable value.
exclusiveMinimum	If "exclusiveMinimum" is present and has boolean value true, the instance is valid if it is strictly greater than the value of "minimum".
maximum	This is the constraint to be put on the value and represents maximum acceptable value.
exclusiveMaximum	If "exclusiveMaximum" is present and has boolean value true, the instance is valid if it is strictly lower than the value of "maximum".
multipleOf	A numeric instance is valid against "multipleOf" if the result of the division of the instance by this keyword's value is an integer.
maxLength	The length of a string instance is defined as the maximum number of its characters.
minLength	The length of a string instance is defined as the minimum number of its characters.
pattern	A string instance is considered valid if the regular expression matches the instance successfully.

You can check a http://json-schema.org for the complete list of keywords that can be used in defining a JSON schema. The above schema can be used to test the validity of the following JSON code

How to Run the application

First, install jsonschema using pip command.

pip install jsonschema

Run the following, will validate the given json input against user_schema.json

python json_validate.py 

Input Json

{"id" : 10,"name": "DonOfDen","contact_number":1234567890}

Testing

Lets test with alternative json input, If you check json_validate.py The validate() method will raise an exception if given JSON is not what is described in the schema.

{"id" : "10","name": "DonOfDen","contact_number":1234567890}

In the above input json we have modified "id" : 10 from integer to "id" : "10" string.

'10' is not of type 'integer'

Failed validating 'type' in schema['properties']['id']:
    {'description': 'The unique identifier for a user', 'type': 'integer'}

On instance['id']:
    '10'
Given JSON data is InValid

Reference:

• https://json-schema.org/
• https://pynative.com/python-json-validation/
• https://www.tutorialspoint.com/json/json_schema.htm
• https://github.com/Julian/jsonschema