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DiceDB

HEXISTS

The HEXISTS command in DiceDB checks if a specified field exists within a hash stored at a given key. This command is used to verify the presence of a field within hash data structures, making it essential for conditional logic.

Syntax

Terminal window
HEXISTS key field

Parameters

ParameterDescriptionTypeRequired
keyThe name of the key holding a hashStringYes
fieldThe field to check within the hashStringYes

Return values

ConditionReturn Value
If the field exists within the hash1
If the field does not exist within the hash0

Behaviour

  • The HEXISTS command checks if the specified field exists within the hash stored at key.
  • If the specified field is present in the hash, HEXISTS returns 1.
  • If the specified field is not present or if key does not contain a hash, it returns 0.
  • If key does not exist, HEXISTS returns 0.

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. Invalid syntax or missing parameter:

    • Error Message: (error) ERR syntax error
    • Occurs if the syntax is incorrect or required parameters (key and field) are missing.

Example Usage

Basic Usage

Checking if field name exists in the hash stored at key user:1001

Terminal window
127.0.0.1:7379> HEXISTS user:1001 name
1

If the field name is not present

Terminal window
127.0.0.1:7379> HEXISTS user:1001 age
0

Checking non-existent key

If the hash user:1002 does not exist:

Terminal window
127.0.0.1:7379> HEXISTS user:1002 name
0

Best Practices

  • Check for Field Existence: Use HEXISTS to check for a field’s existence in conditional logic, especially if subsequent commands depend on the field’s presence.

Alternatives

  • HGET: The HGET command retrieves the value of a specified field within a hash. However, unlike HEXISTS, it returns nil if the field does not exist, rather than a boolean response.

Notes

  • If key is not of type hash, consider using commands specifically designed for other data types.

By utilizing the HEXISTS command, you can conditionally manage hash data in DiceDB, verifying field presence before performing operations based on field existence.