Node Redis WRONGTYPE Operation Error: Causes & Fixes

Learn how to fix the WRONGTYPE Operation Error in Node Redis. Our Redis Support team is here to help you with your questions and concerns.

Node Redis WRONGTYPE Operation Error: Causes & Fixes

Redis is a powerful in-memory data structure store widely used in web applications for caching, session management, and real-time data handling. However, if you have worked with Redis in PHP, especially with frameworks like Laravel, you may have run into this error:

WRONGTYPE Operation against a key holding the wrong kind of value

In this blog, we’ll examine what causes this error, how to diagnose it, and how to fix it.

What Is the “WRONGTYPE” Error in Redis?

This error occurs when we try to execute a Redis command on a key whose stored data type doesn’t match the command’s expected type.

For example, imagine we want to get all fields of a hash using `HGETALL <key>`, but the key stores a string or a list. Redis throws the “WRONGTYPE” error because `HGETALL` only works on hashes.

If you’re interested in resolving similar Redis startup or runtime errors, you might also find our guide on Redis failed to start – Advanced key value store error helpful.

Common Causes of the Error

• Using the wrong Redis command on a key storing a different data type.
• Writing a string to a key previously storing a list, or vice versa.
• Keys that expired or were reused in different contexts without being cleared.
• Calling commands incompatible with the stored key’s data type, often due to inconsistent coding.

If you’re working on a large Redis dataset and need to reset keys with a common naming convention, refer to our tutorial on deleting all Redis keys with a specific prefix.

Redis Data Types and Their Commands

Redis supports six main data types, each requiring specific commands to retrieve their values correctly:

We can use the command `TYPE <key>` in the Redis CLI to check the actual data type stored for a key:

redis> TYPE persons

string

Knowing this is crucial because the error usually means we tried pushing or retrieving data with a command incompatible with the key’s existing data type.

Diagnosing and Fixing the Error: Real-Life Examples

1. PHP Laravel Redis Usage

Suppose we initially set a key `persons` as a string:

$redis->set('persons', $persons);

Later, we want to store multiple persons as a hash:

foreach ($persons as $person) {

$redis->hSet('persons', $person->id, $person);

}

This will trigger the `WRONGTYPE` error because the key `persons` was originally a string, and now we are trying to treat it as a hash.

We can fix this by deleting the existing key first using the Redis CLI:

redis-cli> DEL persons

Then rerun the hash commands. Redis does not allow mixing data types for the same key without deletion.

Then you can safely use hSet.

Our article on the correct usage of ActionCable with Redis covers related best practices for developers integrating Redis with ActionCable or WebSocket-based applications.

2. Node.js with JSON Stored in Redis

If we stored JSON data using a Redis module like RedisJSON (`JSON.SET`), trying to fetch it with a plain `GET` causes the error:

// Incorrect

await client.get(key);

// Correct

await client.json.get(key);

Make sure to use the right command consistent with how the data was stored.

3. Working with .NET Core and Redis

In some .NET Core applications using `IDistributedCache`, data may be stored as a hash even when you expect a string. Using `KeyTypeAsync` helps confirm this.

The fix is to read the hash properly, for example:

var entries = await redisConnection.GetDatabase().HashGetAllAsync("stringKey");

var data = entries.FirstOrDefault(e => e.Name == "data").Value.ToString();

Don’t rely on the order of hash fields, always select by field name.

While diagnosing Redis errors, you may sometimes encounter redirection or sharding-related issues, like the “Benchmark error from server: MOVED” error. If you do, check out our detailed guide on fixing Redis MOVED benchmark errors.

Additional Tips

• Sometimes the error happens because we are connected to the wrong Redis database index. Use `SELECT <db_number>` to switch databases in the Redis CLI.
• Use `KEYS *` to list all keys and `TYPE <key>` to check types before running commands.
• Use the correct Redis command matching the key’s data type.
• Avoid reusing keys for different data types without deleting them first.
• Ensure consistent use of Redis commands in the PHP or other language code.

[Need assistance with a different issue? Our team is available 24/7.]

Conclusion

By understanding Redis data types and carefully managing your keys, you can prevent these errors and make your PHP applications more robust and reliable.

In brief, our Support Experts demonstrated how to fix the WRONGTYPE Operation Error in Node Redis.