How To Manage Hashes in Redis

To create a hash, run the hset command. This command accepts the name of the hash key, the field string, and the corresponding value string as arguments:

hset poet:Verlaine nationality French

hset returns (integer) 1 if the field specified is a new field and the value was set correctly:

Output
(integer) 1

If, however, you fail to include a value, field, or name for the hash key, hset will return an error.

Also, note that hset will overwrite the contents of the hash if it already exists:

hset poet:Verlaine nationality Francais

If the field already exists and its value was updated successfully, hset will return (integer) 0:

Output
(integer) 0

You can also use hsetnx to add fields to hashes, but it will only work if the field does not yet exist. If the specified field does already exist, the hsetnx won’t have any effect and will return (integer) 0:

hsetnx poet:Verlaine nationality French

Output
(integer) 0

To set multiple field/value pairs to a given set, use the hmset command followed by the corresponding field/value strings:

hmset poet:Verlaine born 1844 died 1896 genre Decadent

hmset will return OK if it is successful.

You can determine if a field exists for a given hash with the hexists command:

hexists poet:Verlaine nationality

hexists will return (integer) 1 if the field does exist, and (integer) 0 if it doesn’t.

To return a field’s value, run the hget command followed by the hash key and the field whose value you want to retrieve:

hget poet:Verlaine nationality

Output
"Francais"

hmget uses the same syntax, but can return the values of multiple fields:

hmget poet:Verlaine born died

Output
1) "1844"
2) "1896"

If the hash you pass to hget or hmget does not exist, both commands will return (nil):

hmget poet:Dickinson born died

Output
1) (nil)
2) (nil)

To obtain a list of all the fields held within a certain hash, run the hkeys command:

hkeys poet:Verlaine

Output
1) "nationality"
2) "born"
3) "died"
4) "genre"

Conversely, run hvals to retrieve a list of values held within a hash:

hvals poet:Verlaine

Output
1) "French"
2) "1844"
3) "1896"
4) "Decadent"

To return a list of every field held by a hash and their associated values, run hgetall:

hgetall poet:Verlaine

Output
1) "nationality"
2) "French"
3) "born"
4) "1844"
5) "died"
6) "1896"
7) "genre"
8) "Decadent"

You can find the number of fields in a hash by running hlen, which stands for “hash length”:

hlen poet:Verlaine

Output
(integer) 4

You can find the length of the value string associated with a field with hstrlen, which stands for “hash string length”:

hstrlen poet:Verlaine nationality

Output
(integer) 8

hlen will return (integer) 0 if the hash does not exist.

To delete a field from a hash, run the hdel command. hdel can accept multiple fields as arguments, and will return an integer indicating how many fields were removed from the hash:

hdel poet:Verlaine born died

Output
(integer) 2

If you pass a field that does not exist to hdel, it will ignore that field but delete any other existing fields you specify.

This guide details a number of commands used to create and manage hashes in Redis. If there are other related commands, arguments, or procedures you’d like to learn about in this guide, please ask or make suggestions in the comments.

For more information on Redis commands, check out our tutorial series on How to Manage a Redis Database.