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DiceDB

SMEMBERS

The SMEMBERS command retrieves all members from a set stored at a specified key in DiceDB. Sets are unordered collections of unique strings, and this command provides a way to access all elements within a set for inspection or processing.

Syntax

Terminal window
SMEMBERS key

Parameters

ParameterDescriptionTypeRequired
keyThe key identifying the set to retrieve members fromstringYes

Return values

ConditionReturn Value
Key exists and is a setArray containing all members of the set
Key does not existEmpty array
Key exists but is not a setError message indicating wrong type

Behaviour

  • Checks if the provided key exists in the database
  • Verifies if the key is associated with a set data structure
  • If key exists and is a set, retrieves all members from the set
  • Returns an empty array if the key doesn’t exist
  • Returns error if key exists but holds a different data type
  • The order of elements in the returned array is not guaranteed to be consistent

Errors

  1. Wrong type of key:
    • Error Message: (error) WRONGTYPE Operation against a key holding the wrong kind of value
    • Occurs when attempting to use SMEMBERS on a key that contains a non-set value

Example Usage

Basic Usage

Terminal window
127.0.0.1:7379> SADD myset "apple" "banana" "cherry"
(integer) 3
127.0.0.1:7379> SMEMBERS myset
1) "apple"
2) "banana"
3) "cherry"

Empty Set

Terminal window
127.0.0.1:7379> SMEMBERS nonexistentset
(empty array)

Invalid Usage

Terminal window
127.0.0.1:7379> SMEMBERS
(error) ERR wrong number of arguments for 'smembers' command

Wrong Type Error

Terminal window
127.0.0.1:7379> SET mystring "hello"
OK
127.0.0.1:7379> SMEMBERS mystring
(error) WRONGTYPE Operation against a key holding the wrong kind of value

Best Practices

  1. Always verify the key type before using SMEMBERS to avoid type errors
  2. Implement proper error handling in your application for WRONGTYPE errors
  3. Use EXISTS command to check for key presence before SMEMBERS if key existence is uncertain

Notes

  1. The command returns all members at once, which may impact performance for very large sets
  2. The order of returned elements is not guaranteed and may vary between calls
  3. Memory usage scales linearly with the size of the set
  4. This command has O(N) time complexity where N is the set size