Validation

Input Validation

Jazzy includes a powerful validation engine. It allows you to define validation rules for incoming JSON data in a declarative way.

Basic Usage

The ctx.validate() helper automatically parses the request body and validates it against your rules. If validation fails, Jazzy will automatically return a 422 Unprocessable Entity response with detailed error messages.

import jazzy

proc register(ctx: Context) {.async.} =
  let data = ctx.validate(%*{
    "username": "required|min:3|max:20",
    "email":    "required|email",
    "age":      "int|min:18"
  })

  # If we reach here, validation PASSED.
  # 'data' is a JsonNode containing the validated input.

  let user = DB.table("users").insert(data)
  ctx.json(%*{"status": "success", "id": user})

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Available Validation Rules

• required: The field must be present and not empty.
• string, int, bool, float, json: Type checks.
• email: Validates basic email format.
• min:X: Minimum length (string/array) or minimum value (int/float).
• max:X: Maximum length (string/array) or maximum value (int/float).
• in:foo,bar,baz: The value must be one of the listed options.

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Advanced Usage

Automatic 422 Handling

By default, if ctx.validate() fails, it throws a ValidationError. Jazzy catches this automatically and returns a standardized JSON response:

{
  "errors": {
    "username": "Field 'username' is required",
    "age": "Field 'age' must be at least 18"
  }
}

Manual Validation

If you want to validate a JsonNode manually without the automatic 422 response, you can catch the error:

proc manualValidation(ctx: Context) {.async.} =
  try:
    let data = ctx.validate(%*{"title": "required"})
  except ValidationError as e:
    # Custom error handling logic
    ctx.status(400).json(%*{"my_custom_errors": e.errors})