MGET

The MGET command in DiceDB is used to retrieve the values of multiple keys in a single call. This command is particularly useful for reducing the number of round trips between the client and the server when you need to fetch multiple values.

Syntax

MGET key [key ...]

Parameters

Parameter	Description	Type	Required
key	One or more keys for which the values need to be retrieved. Each key is a string.	String	Yes

Return Value

The MGET command returns an array of values corresponding to the specified keys. If a key does not exist, the corresponding value in the array will be nil.

Condition	Return Value
All specified keys exist	An array of values corresponding to the specified keys
Some keys do not exist	An array where non-existent keys have nil as their value
Keys are of the wrong type	error

Behaviour

• The MGET command retrieves the values of multiple specified keys in the same order as they are listed in the command.
• If a key does not exist, its corresponding position in the returned array will contain nil.
• If any of the keys hold non-string values (e.g., lists or sets), the MGET command will return an error indicating that the operation was attempted on the wrong type of key.

Errors

The MGET command can raise errors in the following scenarios:

1. Wrong type of value or key:

   • Error Message: (error) WRONGTYPE Operation against a key holding the wrong kind of value
   • Occurs when one of the keys holds a value that is not a string.

2. Invalid syntax:

   • Error Message: (error) ERR wrong number of arguments for 'mget' command
   • Occurs when the command is issued without any keys.

Example Usage

Basic Example

Retrieving the values of multiple keys key1, key2, and key3:

127.0.0.1:7379> SET key1 "value1"
OK

127.0.0.1:7379> SET key2 "value2"
OK

127.0.0.1:7379> SET key3 "value3"
OK

127.0.0.1:7379> MGET key1 key2 key3
1) "value1"
2) "value2"
3) "value3"

Example with Non-Existent Keys

127.0.0.1:7379> SET key1 "value1"
OK

127.0.0.1:7379> SET key2 "value2"
OK

127.0.0.1:7379> MGET key1 key2 key3
1) "value1"
2) "value2"
3) (nil)

Key doesn’t exist previously

127.0.0.1:7379> SET key1 "value1"
OK

127.0.0.1:7379> LPUSH key2 "value2"
(integer) 1

127.0.0.1:7379> MGET key1 key2
1) "value1"
2) (nil)

Key exists previously with different datatype

127.0.0.1:7379> SET key1 "value1"
OK

127.0.0.1:7379> SET key2 "value2"
OK

127.0.0.1:7379> LPUSH key2 "value3"
(error) ERROR WRONGTYPE Operation against a key holding the wrong kind of value

127.0.0.1:7379> MGET key1 key2
1) "value1"
2) "value2"

Notes

• The MGET command is atomic, meaning that it will either retrieve all the specified keys or none if an error occurs.
• The order of the returned values matches the order of the specified keys.
• Using MGET can be more efficient than multiple GET commands, especially when dealing with a large number of keys.

Best Practices

• Ensure that all specified keys are of the string type to avoid WRONGTYPE errors.
• Use MGET to minimize the number of round trips to the DiceDB server when you need to fetch multiple values.
• Handle nil values in the returned array appropriately in your application logic to account for non-existent keys.

By following this documentation, you should be able to effectively use the MGET command in DiceDB to retrieve multiple values efficiently and handle any potential errors that may arise.