HMSET

The HMSET command in DiceDB is used to set multiple field-value pairs in a hash at once. If the hash does not exist, a new hash is created. This command is efficient for setting multiple fields at once within a hash data structure.

Syntax

HMSET key field value [field value ...]

Parameters

Parameter	Description	Type	Required
key	The name of the hash.	String	Yes
field	The field within the hash to set the value for.	String	Yes
value	The value to set for the specified field.	String	Yes
[field value ...]	Additional field-value pairs to set in the hash.	String	No

Return Values

Condition	Return Value
A new field added	OK
Existing field updated	OK
Multiple fields added	OK
Non-hash type or wrong data type	(error) WRONGTYPE Operation against a key holding the wrong kind of value
Incorrect Argument Count	(error) ERR wrong number of arguments for 'hmset' command

Behaviour

When the HMSET command is executed, the following actions occur:

• If the specified hash does not exist, a new hash is created.
• The specified fields and values are set in the hash.
• If any field already exists, its value is updated with the new value provided.
• The command returns OK to indicate successful execution.

Errors

The HMSET command can raise errors in the following scenarios:

1. Non-hash type or wrong data type:

   • Error Message: (error) WRONGTYPE Operation against a key holding the wrong kind of value
   • Occurs if key holds a non-hash data structure.

2. Incorrect Argument Count:

   • Error Message: (error) ERR wrong number of arguments for 'hmset' command
   • Occurs if the command is not provided with the correct number of arguments (i.e., an even number of arguments after the key).

Example Usage

Creating a New Hash with Multiple Fields

127.0.0.1:7379> HMSET product:4000 name "Tablet" price 299.99 stock 30
OK

Updating an Existing Hash with Multiple Fields

127.0.0.1:7379> HMSET product:4000 price 279.99 stock 25
OK

Invalid Usage

Trying to set fields in a key that is not a hash.

127.0.0.1:7379> SET product:4000 "This is a string"
OK
127.0.0.1:7379> HMSET product:4000 name "Tablet"
(error) WRONGTYPE Operation against a key holding the wrong kind of value

Wrong Number of Arguments for HMSET Command

127.0.0.1:7379> HMSET product:4000
(error) ERR wrong number of arguments for 'hmset' command

127.0.0.1:7379> HMSET product:4000 name
(error) ERR wrong number of arguments for 'hmset' command

Best Practices

• Use HMSET for Batch Updates: Utilize HMSET when you need to set multiple fields at once in a hash to reduce command overhead and improve performance.