In Redis, the MSETNX command allows us to set multiple keys at once, but only if none of them exist.

This allows us to set multiple keys representing different fields of a single logical object in a way that ensures that either all the fields are set, or none are set.

Syntax

The syntax goes like this:

MSETNX key value [ key value ...]

Which basically means we can set multiple key/value pairs at once.

Example

Here’s a simple example to demonstrate:

MSETNX name "Woof" type "Dog" age "10"

Result:

(integer) 1

In this case, the MSET operation was successful, and so we got an integer reply of 1.

We can now use the MGET command to return the values of each of those keys. Here’s an example of doing just that:

MGET name type age

Result:

1) "Woof"
2) "Dog"
3) "10"

When a Key Already Exists

As mentioned, if any of the keys already exist, nothing is set. Here’s an example:

MSETNX name "Big Woof" age "11"

Result:

(integer) 0

We get an integer reply of 0, which means nothing was set.

Now let’s get the values again:

MGET name type age

Result:

1) "Woof"
2) "Dog"
3) "10"

As expected, the values haven’t changed since the first example.

If this is a problem for you, use MSET instead. The MSET command overwrites any existing values with the new value.