HMSET

Introduction and Use Case(s)

HMSET is a Redis command used to set multiple fields in a hash stored at a key. This command is useful when you need to store or update multiple related data points under a single key, such as user profiles, configuration settings, or other structured data.

Syntax

  1. HMSET key field1 value1 [field2 value2 ...]

Parameter Explanations

  • key: The name of the hash where the fields are to be set.
  • field1 value1: The first field-value pair to set in the hash.
  • field2 value2 (optional): Additional field-value pairs to set in the hash.

Return Values

HMSET returns a simple string reply indicating success.

Example:

  1. "OK"

Code Examples

  1. dragonfly> HMSET user:1000 username "john_doe" age "30" city "New York"
  2. "OK"
  3. dragonfly> HGETALL user:1000
  4. 1) "username"
  5. 2) "john_doe"
  6. 3) "age"
  7. 4) "30"
  8. 5) "city"
  9. 6) "New York"

Best Practices

  • Use descriptive and consistent naming conventions for keys and fields to maintain clarity.
  • If possible, prefer HSET over HMSET, as the latter is deprecated since Redis 4.0. Instead of HMSET, use multiple HSET operations.

Common Mistakes

Using HMSET on an already existing key with conflicting data type

Make sure the key does not hold a non-hash value, or HMSET will return an error.

  1. dragonfly> SET mystring "a string"
  2. "OK"
  3. dragonfly> HMSET mystring field1 "value1"
  4. (error) WRONGTYPE Operation against a key holding the wrong kind of value

FAQs

What happens if one of the fields already exists?

If a field already exists, HMSET will overwrite its value without returning an error.

Is HMSET atomic?

Yes, HMSET is an atomic operation, meaning all field-value pairs are set simultaneously.