Скачать или смотреть Resolving TypeScript to JavaScript Model Issues in Your API Development

Find out how to fix the `TypeScript` to `JavaScript` transpilation issues in your API, ensuring your models load correctly in a Postgres database.
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This video is based on the question https://stackoverflow.com/q/62919051/ asked by the user 'Wincenty Bertoni Lech' ( https://stackoverflow.com/u/5131473/ ) and on the answer https://stackoverflow.com/a/62966616/ provided by the user 'Sunny Goel' ( https://stackoverflow.com/u/10346580/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting Your API: Fixing Transpilation Issues with TypeScript Models

When developing an API with TypeScript, it’s common to encounter issues during the transpilation process—especially when it comes to loading models. If you're facing an error stating that your model can't be found once you've transpiled your TypeScript code to JavaScript, you're not alone.

The Problem in Detail

While using ts-node-dev, your API may run without issues, but once you transpile the files with Babel and attempt to run the built JavaScript files, you might run into errors. Specifically, you're likely to see syntax errors or issues regarding metadata for your models during HTTP requests.

Let's break this down:

Syntax Error During Import:

When transpiled, the TypeScript files are converted into JavaScript. If your import statements or TypeScript decorators are not correctly handled in the transpilation process, it can lead to syntax errors.

Metadata Not Found:

Upon trying to query the database, you may receive an error indicating that no metadata for a specific model (like your Student model) was found, showcasing that the model definitions may not be loaded properly.

The Solution: Fixing the Configuration

The root of the issue lies in your ormconfig.ts, which is responsible for determining how TypeORM interfaces with your models and database. Here's how we can fix it:

Step 1: Update Your ormconfig.ts

Your current ormconfig.ts specifies the path to the TypeScript files, which won't be valid after transpilation. Change your configuration to support both TypeScript and JavaScript by modifying the entities and migrations paths.

Original Configuration

[[See Video to Reveal this Text or Code Snippet]]

Updated Configuration

Replace the above line with:

[[See Video to Reveal this Text or Code Snippet]]

This change allows TypeORM to look for entity files in both TypeScript and JavaScript formats. The ${.ts,.js} allows matching files regardless of whether they were transpiled or not.

Step 2: Further Configuration (Optional)

If you need to specify migrations or any other files, ensure that similar logic is applied to those paths as well. Here’s how you can revise the migrations entry:

Original Migrations Configuration

[[See Video to Reveal this Text or Code Snippet]]

Updated Migrations Configuration

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Once these changes are implemented, you should be able to run your API after transpiling without encountering model loading issues. Both your TypeScript models and the JavaScript transpiled versions will be correctly recognized by TypeORM.

By addressing these configuration issues, you streamline the development process and avoid common pitfalls associated with using TypeScript and JavaScript interchangeably.

If you continue to face errors, double-check the paths and ensure that your transpilation process is correctly set up to produce the necessary files in the expected directory structure. With these adjustments, your API should function seamlessly across both development and production environments.

Happy coding!