HVALS

Introduction and Use Case(s)

The HVALS command in Redis is used to retrieve all the values stored in a hash. This command is particularly useful when you need to access all the values without knowing their corresponding fields. Typical use cases include aggregating data for reporting, extracting information for processing, or simply displaying all associated values of a particular key.

Syntax

  1. HVALS key

Parameter Explanations

  • key: The name of the hash from which you want to retrieve all values. It must be an existing hash key; otherwise, an empty list is returned.

Return Values

The HVALS command returns a list of values contained in the hash. If the hash does not exist, it returns an empty list.

Example Outputs:

  1. When the hash exists:

    1. 1) "value1"
    2. 2) "value2"
    3. 3) "value3"

  2. When the hash does not exist:

    1. (empty list or set)

Code Examples

  1. dragonfly> HSET myhash field1 "Hello"
  2. (integer) 1
  3. dragonfly> HSET myhash field2 "World"
  4. (integer) 1
  5. dragonfly> HVALS myhash
  6. 1) "Hello"
  7. 2) "World"

Best Practices

  • Ensure that the key provided is indeed a hash type to avoid unexpected results.
  • Utilize the HEXISTS command before HVALS if there’s uncertainty about the existence of the key.

Common Mistakes

  • Using HVALS on a non-hash key will result in an error. Always ensure the key type is a hash.

    1. dragonfly> SET mystring "value"
    2. OK
    3. dragonfly> HVALS mystring
    4. (error) WRONGTYPE Operation against a key holding the wrong kind of value

FAQs

What happens if the hash key does not exist?

If the specified hash key does not exist, HVALS will return an empty list.

Can I use HVALS with large hashes?

Yes, but be cautious as retrieving a large number of values can be resource-intensive. For large data sets, consider using pagination or other methods to manage data retrieval efficiently.