GETSET

The GETSET command in DiceDB is a powerful atomic operation that combines the functionality of GET and SET commands. It retrieves the current value of a key and simultaneously sets a new value for that key. This command is particularly useful when you need to update a value and also need to know the previous value in a single atomic operation.

Syntax

GETSET key value

Parameters

Parameter	Description	Type	Required
key	The key whose value you want to retrieve and set.	String	Yes
value	The new value to set for the specified key.	String	Yes

Return values

Condition	Return Value
The old value stored at the specifiied key	A string value
The key does not exist	nil

Behaviour

When the GETSET command is executed, the following sequence of actions occurs:

1. The current value of the specified key is retrieved.
2. The specified key is updated with the new value.
3. If the specified key had an existing TTL , it is reset.
4. The old value is returned to the client.

This operation is atomic, meaning that no other commands can be executed on the key between the get and set operations.

Errors

The GETSET command can raise errors in the following scenarios:

1. Wrong Type Error: If the key exists but is not a string, DiceDB will return an error.
   • Error Message: (error) ERROR WRONGTYPE Operation against a key holding the wrong kind of value
2. Syntax Error: If the command is not provided with exactly two arguments (key and value), DiceDB will return a syntax error.
   • Error Message: (error) ERROR wrong number of arguments for 'getset' command

Examples

Basic Example

127.0.0.1:7379> SET mykey "Hello"
127.0.0.1:7379> GETSET mykey "World"
"Hello"

• The initial value of mykey is set to “Hello”.
• The GETSET command retrieves the current value “Hello” and sets the new value “World”.
• The old value “Hello” is returned.

Example with Non-Existent Key

127.0.0.1:7379> GETSET newkey "NewValue"
(nil)

• The key newkey does not exist.
• The GETSET command sets the value of newkey to “NewValue”.
• Since the key did not exist before, nil is returned.

Example with Key having pre-existing TTL

127.0.0.1:7379> SET newkey "test"
OK
127.0.0.1:7379> EXPIRE newkey 60
1
127.0.0.1:7379> TTL newkey
55
127.0.0.1:7379> GETSET newkey "new value"
"test"
127.0.0.1:7379> TTL newkey
(integer) -1

• The newkey used in the GETSET command had an existing TTL set to expire in 60 seconds
• When GETSET is executed on the mentioned key, it updates the value and resets the TTL on the key.
• Hence, the TTL on newkey post GETSET returns -1 , suggesting that the key exists without any TTL configured

Wrong Type

127.0.0.1:7379> LPUSH mylist "item"
127.0.0.1:7379> GETSET mylist "NewValue"
(error) ERROR WRONGTYPE Operation against a key holding the wrong kind of value

• The key mylist is a list, not a string.
• The GETSET command cannot operate on a list and returns a WRONGTYPE error.

Syntax Error

127.0.0.1:7379> GETSET mykey
(error) ERROR wrong number of arguments for 'getset' command

• The GETSET command requires exactly two arguments: a key and a value.
• Since only one argument is provided, DiceDB returns a syntax error.