HKEYS

Introduction and Use Case(s)

The HKEYS command in Redis is used to retrieve all the keys (fields) in a hash stored at a specified key. This command is particularly useful when you need to inspect the structure of a hash or iterate over its fields for further processing.

Syntax

  1. HKEYS key

Parameter Explanations

  • key: The name of the hash from which to retrieve the fields. If the hash does not exist, an empty list is returned.

Return Values

The HKEYS command returns a list of strings, each representing a field in the hash.

Example Outputs

  • If the hash contains fields: ["field1", "field2", "field3"]
  • If the hash is empty or does not exist: []

Code Examples

  1. dragonfly> HSET myhash field1 "value1" field2 "value2"
  2. (integer) 2
  3. dragonfly> HKEYS myhash
  4. 1) "field1"
  5. 2) "field2"
  6. dragonfly> HDEL myhash field1
  7. (integer) 1
  8. dragonfly> HKEYS myhash
  9. 1) "field2"
  10. dragonfly> DEL myhash
  11. (integer) 1
  12. dragonfly> HKEYS myhash
  13. (empty array)

Best Practices

  • Ensure that the key exists and is of type hash before calling HKEYS to avoid unnecessary operations.
  • Combine HKEYS with other hash commands like HGETALL or HVALS for more comprehensive data manipulations.

Common Mistakes

  • Attempting to use HKEYS on a key that is not a hash will result in an error. Always verify the data type if unsure.
  • Forgetting to check if the hash is empty can lead to assumptions that the key doesn’t exist.

FAQs

What happens if the key does not exist?

If the specified key does not exist, HKEYS returns an empty list.

Can I use HKEYS on non-hash data types?

No, using HKEYS on a key that holds a non-hash value results in an error.