Fix “WRONGTYPE Operation against a key holding the wrong kind of value” when using ZINTER in Redis

If you get an error that reads “WRONGTYPE Operation against a key holding the wrong kind of value” when using the ZINTER command in Redis, it’s probably because you’re passing a key with the wrong data type.

To fix this issue, be sure that each key you pass to the ZINTER command is either a set or a sorted set.

Example of Error

Here’s an example of code that causes the error:

ZINTER 2 cats country

Result:

(error) WRONGTYPE Operation against a key holding the wrong kind of value

In my case, the cats key holds a sorted set but the country key holds a string, which is why I got the error.

We can use the TYPE command to check a key’s type:

TYPE country

Result:

string

As suspected, the key holds a string, which is the wrong data type for the ZINTER command.

The cats key is fine though:

TYPE cats

Result:

zset

This means that it’s a sorted set, which is the correct data type.

Solution

The solution is to make sure the keys we pass contain the correct data type. The ZINTER command is designed to be used on sorted sets, but it can also work on (non-sorted) sets, so we should make sure the keys contain one of those data types.

In our above example, the cats key is fine (because it holds a sorted set) but the country key is what caused the error. This is because it doesn’t hold a sorted set (it holds a string).

Let’s replace the country key with another key that holds a sorted set:

ZINTER 2 cats dogs

Result:

1) "fluffy"
2) "scratch"

This time we didn’t get the error. That’s because both keys hold a sorted set.

As mentioned non-sorted sets are also fine:

ZINTER 2 cats users

Result:

1) "fluffy"
2) "scratch"

Here, I replaced the dogs key with one called users. The users key actually holds a (non-sorted) set. We can verify this with the TYPE command:

TYPE users

Result:

set

As suspected, it’s a set, but it doesn’t cause any issues with the ZINTER command.