HKEYS

The HKEYS command in DiceDB retrieves all fields in a hash stored at a given key. This command is essential for working with hash data structures, enabling retrieval of all field names for dynamic inspection or iteration.

Syntax

HKEYS key

Parameters

Parameter	Description	Type	Required
key	The name of the key holding a hash	String	Yes

Return values

Condition	Return Value
If the key exists and holds a hash	Array of field names
If the key does not exist or is empty	Empty array []

Behaviour

• The HKEYS command retrieves all field names within the hash stored at the specified key.
• If the hash is empty or the key does not exist, it returns an empty array [].
• If key exists but does not hold a hash, an error is returned.

Errors

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, such as a string or list.

2. Missing required parameter:

   • Error Message: (error) ERR wrong number of arguments for 'HKEYS' command
   • Occurs if the key parameter is missing from the command.

Example Usage

Basic Usage

Retrieving all field names in the hash stored at key user:1001

127.0.0.1:7379> HKEYS user:1001
1) "name"
2) "age"
3) "email"

Empty hash

If the hash stored at user:1002 exists but has no fields:

127.0.0.1:7379> HKEYS user:1002
(nil)

Non-existent key

If the hash user:1003 does not exist:

127.0.0.1:7379> HKEYS user:1003
(nil)

Best Practices

• Use Before Iterating: Use HKEYS to retrieve field names in dynamic applications where the field names may not be predetermined.

Alternatives

• HGETALL: The HGETALL command retrieves all field-value pairs in a hash as an array, rather than only the field names.

Notes

• Ensure that key is of type hash before using HKEYS, as other data types will produce errors.

Using the HKEYS command, you can efficiently access all field names in hash structures, making it a valuable tool for dynamic data inspection in DiceDB.