Task 08 — Add Input Validation with JSON Schema

Difficulty: Intermediate–Advanced
Goal: Add structured JSON Schema validation to a POST endpoint so malformed requests are rejected early with clear error messages, before they reach the service layer.

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What you'll learn

• How app/validators/ works (schema.py, validator_util.py, schemas/)
• How to write a JSON Schema for a request body
• How the @validate_values() decorator and input_validator.py fit together
• How to write unit tests for the validator

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Your task: Validate a "Create Alert Rule" request

Assume you have (or will build) a POST /api/admin/alerts/rules endpoint.
The request body should look like:

{
  "industryId": "IND001",
  "unitId": "U001",
  "alertType": "HIGH_CONDUCTIVITY",
  "threshold": 1500,
  "channels": ["email", "sms"]
}

Write a JSON Schema that enforces:

• industryId, unitId, alertType — required strings, no empty values
• threshold — required number, minimum 0
• channels — required array, at least one item, items must be one of ["email", "sms", "chat"]

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Files to create / edit

File	What to do
app/validators/schemas/create_alert_rule.json	JSON Schema definition
app/validators/schema.py	Load and register the schema
app/routes/admin/alert_rules.py	Call the validator before the service

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Schema file

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "CreateAlertRule",
  "type": "object",
  "required": ["industryId", "unitId", "alertType", "threshold", "channels"],
  "properties": {
    "industryId": { "type": "string", "minLength": 1 },
    "unitId":     { "type": "string", "minLength": 1 },
    "alertType":  { "type": "string", "minLength": 1 },
    "threshold":  { "type": "number", "minimum": 0 },
    "channels": {
      "type": "array",
      "minItems": 1,
      "items": { "type": "string", "enum": ["email", "sms", "chat"] }
    }
  },
  "additionalProperties": false
}

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Using the validator in the route

from flask_restx import marshal
from app.validators.validator_util import validate_request_body
from app.models.error_models import GenericErrorModel

@alertRulesNamespace.route('')
class AlertRulesRoute(Resource):
    @jwt_required()
    @admin_required()
    def post(self):
        body = request.get_json()
        error = validate_request_body(body, 'create_alert_rule')
        if error:
            return marshal({'status': 'failed', 'status_code': 1403, 'message': error}, GenericErrorModel), 200

        # proceed to service

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Test cases to write

Input	Expected result
Valid body	200 success
Missing threshold	1403 with descriptive message
channels: []	1403 (minItems not met)
channels: ["fax"]	1403 (enum violation)
threshold: -5	1403 (minimum violation)
Extra field "foo": "bar"	1403 (additionalProperties)

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Done when

• Schema file exists and is registered
• Valid bodies pass through to the service
• Each invalid case returns 1403 with a message that names the failing field
• Tests cover all cases in the table above