schemaValidationMiddleware function

Middleware schemaValidationMiddleware(RouteSchema schema)

Creates a middleware that automatically validates incoming request data against a RouteSchema's validation rules.

This middleware inspects the route's RouteSchema.validationRules and, if present, validates the request body/query parameters using the framework's existing validation pipeline (which selects the appropriate binding — JSON, form, query — based on the HTTP method and content type).

On validation failure, a ValidationError is thrown and caught by the engine's global error handler, which returns a 422 Unprocessable Entity response with detailed field-level error messages.

This middleware is intended to be injected automatically by EngineRoute when a route has a schema with validation rules. It runs just before the route handler in the middleware chain.

Example:

engine.post('/users', createUser, schema: RouteSchema.fromRules({
  'name': 'required|string|min:2',
  'email': 'required|email',
}));

Implementation

Middleware schemaValidationMiddleware(RouteSchema schema) {
  final rules = schema.validationRules;

  return (EngineContext ctx, Next next) async {
    if (rules != null && rules.isNotEmpty) {
      // ctx.validate() delegates to the appropriate binding (JSON, form,
      // query) based on the HTTP method and content type. It throws
      // ValidationError on failure, which the engine's global error handler
      // converts to a 422 response.
      await ctx.validate(rules);
    }
    return next();
  };
}