herodb/specs/backgroundinfo/redis_hset_functions.md

🔑 Redis HSET and Related Hash Commands

1. HSET

• Purpose: Set the value of one or more fields in a hash.

• Syntax:

  HSET key field value [field value ...]
  

• Return:

  • Integer: number of fields that were newly added.

• RESP Protocol:

  *4
  $4
  HSET
  $3
  key
  $5
  field
  $5
  value
  

  (If multiple field-value pairs: *6, *8, etc.)

---

2. HSETNX

• Purpose: Set the value of a hash field only if it does not exist.

• Syntax:

  HSETNX key field value
  

• Return:

  • 1 if field was set.
  • 0 if field already exists.

• RESP Protocol:

  *4
  $6
  HSETNX
  $3
  key
  $5
  field
  $5
  value
  

---

3. HGET

• Purpose: Get the value of a hash field.

• Syntax:

  HGET key field
  

• Return:

  • Bulk string (value) or nil if field does not exist.

• RESP Protocol:

  *3
  $4
  HGET
  $3
  key
  $5
  field
  

---

4. HGETALL

• Purpose: Get all fields and values in a hash.

• Syntax:

  HGETALL key
  

• Return:

  • Array of [field1, value1, field2, value2, ...].

• RESP Protocol:

  *2
  $7
  HGETALL
  $3
  key
  

---

5. HMSET (⚠️ Deprecated, use HSET)

• Purpose: Set multiple field-value pairs.

• Syntax:

  HMSET key field value [field value ...]
  

• Return:

  • Always OK.

• RESP Protocol:

  *6
  $5
  HMSET
  $3
  key
  $5
  field
  $5
  value
  $5
  field2
  $5
  value2
  

---

6. HMGET

• Purpose: Get values of multiple fields.

• Syntax:

  HMGET key field [field ...]
  

• Return:

  • Array of values (bulk strings or nils).

• RESP Protocol:

  *4
  $5
  HMGET
  $3
  key
  $5
  field1
  $5
  field2
  

---

7. HDEL

• Purpose: Delete one or more fields from a hash.

• Syntax:

  HDEL key field [field ...]
  

• Return:

  • Integer: number of fields removed.

• RESP Protocol:

  *3
  $4
  HDEL
  $3
  key
  $5
  field
  

---

8. HEXISTS

• Purpose: Check if a field exists.

• Syntax:

  HEXISTS key field
  

• Return:

  • 1 if exists, 0 if not.

• RESP Protocol:

  *3
  $7
  HEXISTS
  $3
  key
  $5
  field
  

---

9. HKEYS

• Purpose: Get all field names in a hash.

• Syntax:

  HKEYS key
  

• Return:

  • Array of field names.

• RESP Protocol:

  *2
  $5
  HKEYS
  $3
  key
  

---

10. HVALS

• Purpose: Get all values in a hash.

• Syntax:

  HVALS key
  

• Return:

  • Array of values.

• RESP Protocol:

  *2
  $5
  HVALS
  $3
  key
  

---

11. HLEN

• Purpose: Get number of fields in a hash.

• Syntax:

  HLEN key
  

• Return:

  • Integer: number of fields.

• RESP Protocol:

  *2
  $4
  HLEN
  $3
  key
  

12. HSCAN

• Purpose: Iterate fields/values of a hash (cursor-based scan).

• Syntax:

  HSCAN key cursor [MATCH pattern] [COUNT count]
  

• Return:

  • Array: [new-cursor, [field1, value1, ...]]

• RESP Protocol:

  *3
  $5
  HSCAN
  $3
  key
  $1
  0