HSET

The HSET command in DiceDB is used to set the value of a field in a hash. If the hash does not exist, a new hash is created. If the field already exists in the hash, the value is updated. This command is useful for managing and storing key-value pairs within a hash data structure.

Syntax

HSET 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 ...]	Optional additional field-value pairs to set in the hash.	String	No

Return Values

Condition	Return Value
A new field added	1
Existing field updated	0
Multiple fields added	Integer (count of new fields)
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 'hset' command

Behaviour

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

• If the specified hash does not exist, a new hash is created.
• The specified field(s) and value(s) are set in the hash.
• If a field already exists, its value is updated with the new value provided.
• The command returns the number of fields that were newly added to the hash.

Errors

The HSET 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 'hset' 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

127.0.0.1:7379> HSET product:2000 name "Laptop" price 999.99 stock 50
3

Updating an Existing Hash

Updating existing fields in a hash product:2000.

127.0.0.1:7379> HSET product:2000 price 899.99 stock 45

Setting Multiple Field-Value Pairs

Setting multiple fields in a hash user:1000.

127.0.0.1:7379> HSET user:1000 name "John Doe" age 30 email "john.doe@example.com"

Updating Existing Fields

Updating a field in an existing hash user:1000.

127.0.0.1:7379> HSET user:1000 age 31

Invalid Usage

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

127.0.0.1:7379> SET product:2000 "This is a string"
OK
127.0.0.1:7379> HSET product:2000 name "Laptop"
(error) WRONGTYPE Operation against a key holding the wrong kind of value

Wrong Number of Arguments for HSET Command

127.0.0.1:7379> HSET product:2000
(error) ERR wrong number of arguments for 'hset' command

127.0.0.1:7379> HSET product:2000 name
(error) ERR wrong number of arguments for 'hset' command

Best Practices

• Check for Existence: Before updating fields, consider checking if the hash exists to avoid unnecessary updates.

Notes

• HSET can also accept multiple field-value pairs, making it efficient for adding or updating multiple fields in a single command. By understanding the HSET command, you can effectively update or expand hashes in your DiceDB database, allowing for quick modifications and optimizations when handling key-value pairs within hashes.