How to Fix 500 Error in JSON Server DELETE Requests

When using JSON Server, many developers encounter unexpected 500 errors during DELETE requests, even when deletion is successful. These errors often arise due to issues with relationships in the db.json file, particularly null foreign keys. This guide explains the root cause and offers two potential fixes.

Scenario: Why the 500 Error Occurs

The 500 error is not always straightforward. JSON Server attempts to handle data relationships for each DELETE call. When invalid relations (e.g., null foreign keys) exist, it may still return a 500 error despite the deletion working as intended.

Example: Here’s a sample db.json file with invalid relations:

{
  "posts": [
    { "id": "1", "name": "Post 1", "photoId": "photo1" },
    { "id": "2", "name": "Post 2", "photoId": null }
  ],
  "photos": [
    { "id": "photo1", "url": "https://abc.com/1" }
  ]
}

Even when deleting Post 1, which has valid relations, you might still see a 500 error.

Solution 1: Remove Null Foreign Keys

To resolve the error, remove null foreign key properties (e.g., “photoId”: null) from the data file. This ensures that JSON Server processes only valid relationships during DELETE calls.

Downside: If your backend returns null values, removing them can make testing less realistic.

Solution 2: Use a Dummy Foreign Key Suffix

Run JSON Server with the —fks dummy parameter to bypass relation validation:

json-server db.json --fks dummy

Downside: Relations won’t be handled accurately anymore.

Conclusion

While JSON Server is a helpful mock API tool, its handling of relations during DELETE requests can be tricky. No foreign key with id in it’s name should be null. Adjust your data or server behavior depending on your use case to minimize errors.

For more details on the root cause you can refer here, the solution given by opami.