A Smart Way to Write Code in NestJS When a Single Endpoint Can Return Both 200 and 201 Status Codes

When building a RESTful API with NestJS, you may encounter a situation where a single endpoint can return both 200 and 201 status codes, depending on the request payload or specific business logic. This can get tricky, but fear not, dear developer! In this article, we’ll explore a smart way to write code in NestJS to handle this scenario with ease and elegance.

Understanding the Challenge

Imagine you have a `CREATE` endpoint that accepts a new resource payload. In some cases, you might want to return a 200 OK status code when the resource is created successfully, and in other cases, you might need to return a 201 Created status code with a `Location` header pointing to the newly created resource. How do you approach this challenge?

The Naive Approach

A simple solution might be to use an `if-else` statement to determine which status code to return based on the request payload or business logic. However, this approach can lead to cumbersome and hard-to-read code, especially when dealing with multiple possible scenarios.

@Post()
async createResource(@Body() resource: any) {
  if (someCondition) {
    // Return 201 Created
    return res.status(201).json({ message: 'Resource created successfully' });
  } else {
    // Return 200 OK
    return res.status(200).json({ message: 'Resource updated successfully' });
  }
}

A Better Way: Using a Custom Enum

A more elegant solution is to create a custom enum that defines the possible response types for your endpoint. This enum can have values for both 200 and 201 status codes, along with any additional metadata or information you need to include in the response.

enum ResponseType {
  CREATED = 'CREATED',
  UPDATED = 'UPDATED',
}

interface Response {
  type: ResponseType;
  message: string;
  location?: string;
}

@Post()
async createResource(@Body() resource: any) {
  const responseType = someCondition ? ResponseType.CREATED : ResponseType.UPDATED;
  const response: Response = {
    type: responseType,
    message: responseType === ResponseType.CREATED ? 'Resource created successfully' : 'Resource updated successfully',
  };

  if (responseType === ResponseType.CREATED) {
    response.location = '/resources/' + resourceId;
  }

  return res.status(responseType === ResponseType.CREATED ? 201 : 200).json(response);
}

Benefits of Using a Custom Enum

Using a custom enum provides several benefits, including:

• Improved code readability: The enum makes it clear what each response type represents, making the code easier to understand and maintain.
• Reduced code duplication: By defining the response types and metadata in a single place, you can avoid duplicating code for each possible scenario.
• Flexibility: You can easily add or remove response types as needed, without affecting the underlying logic.

Taking it to the Next Level: Using a Response Factory

A response factory is a class or function that takes care of generating the response object based on the request payload and business logic. This approach takes the enum-based solution to the next level, providing even more flexibility and reusability.

class ResponseFactory {
  createResponse(resource: any, responseType: ResponseType) {
    const response: Response = {
      type: responseType,
      message: responseType === ResponseType.CREATED ? 'Resource created successfully' : 'Resource updated successfully',
    };

    if (responseType === ResponseType.CREATED) {
      response.location = '/resources/' + resourceId;
    }

    return response;
  }
}

@Post()
async createResource(@Body() resource: any) {
  const responseType = someCondition ? ResponseType.CREATED : ResponseType.UPDATED;
  const responseFactory = new ResponseFactory();
  const response = responseFactory.createResponse(resource, responseType);

  return res.status(responseType === ResponseType.CREATED ? 201 : 200).json(response);
}

Benefits of Using a Response Factory

Using a response factory provides several benefits, including:

• Decoupling: The response factory decouples the response generation logic from the endpoint logic, making it easier to test and maintain.
• Reusability: You can reuse the response factory across multiple endpoints, reducing code duplication and increasing consistency.
• Customizability: You can easily customize the response factory to generate different types of responses based on specific business logic or requirements.

Conclusion

When dealing with a single endpoint that can return both 200 and 201 status codes, a smart way to write code in NestJS is to use a custom enum and response factory. This approach provides improved code readability, reduced code duplication, and increased flexibility. By following these best practices, you can build robust, maintainable, and scalable APIs that meet the needs of your users.

Best Practices and Additional Tips

Here are some additional best practices and tips to keep in mind when implementing this approach:

1. Use meaningful enum values: Choose enum values that are descriptive and easy to understand, such as `CREATED`, `UPDATED`, or `DELETED`.
2. Keep the response factory lean: Avoid putting too much logic in the response factory. Instead, focus on generating the response object based on the input parameters.
3. Use dependency injection: Consider using dependency injection to inject the response factory into your endpoint, making it easier to test and maintain.
4. Document your API: Don’t forget to document your API using tools like Swagger or API documentation generators, to ensure that your API is easily consumable by clients.

Common Pitfalls to Avoid

Here are some common pitfalls to avoid when implementing this approach:

• Over-engineering: Avoid over-engineering the response factory or enum, keeping it simple and focused on the task at hand.
• Inconsistent response formats: Ensure that the response formats are consistent across different endpoints and scenarios, to avoid confusion and errors.
• Not handling errors properly: Make sure to handle errors and exceptions properly, including logging and error handling mechanisms.

Sidebar: Testing Your API

When testing your API, make sure to cover different scenarios and edge cases, including:

• Happy path testing: Test the happy path where the endpoint returns a 200 or 201 status code successfully.
• Error path testing: Test error scenarios, such as invalid input or internal server errors.
• : Test edge cases, such as large payloads or concurrent requests.

Scenario	Status Code	Response Body
Resource created successfully	201	{ “type”: “CREATED”, “message”: “Resource created successfully”, “location”: “/resources/123” }
Resource updated successfully	200	{ “type”: “UPDATED”, “message”: “Resource updated successfully” }
Invalid input	400	{ “error”: “Invalid input”, “message”: “Please provide valid input” }

By following these best practices and avoiding common pitfalls, you can build a robust and scalable API that meets the needs of your users. Remember to test your API thoroughly and document it properly to ensure a smooth development experience.

Frequently Asked Question

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