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cmd_hset.go

cmd_hset.go - Overview​

This file implements the HSET command, which sets field-value pairs in a string-string map (SSMap) stored at a given key in the DiceDB store.

Detailed Documentation​

SSMap Type​

type SSMap map[string]string
  • Purpose: Represents a string-string map.

cHSET Variable​

var cHSET = &CommandMeta{
	Name:      "HSET",
	Syntax:    "HSET key field value [field value ...]",
	HelpShort: "HSET sets field value in the string-string map stored at key",
	HelpLong: `
HSET sets the field and value for the key in the string-string map.

Returns "OK" if the field value was set or updated in the map. Returns (nil) if the
field value was not set or updated.
	`,
	Examples: `
localhost:7379> HSET k1 f1 v1
OK 1
localhost:7379> HSET k1 f1 v1 f2 v2 f3 v3
OK 2
localhost:7379> HGET k1 f1
OK v1
localhost:7379> HGET k2 f1
OK (nil)
	`,
	Eval:    evalHSET,
	Execute: executeHSET,
}
  • Purpose: Defines the metadata for the HSET command, including its name, syntax, help messages, example usages, and the functions to evaluate and execute the command.

init Function​

func init() {
	CommandRegistry.AddCommand(cHSET)
}
  • Purpose: Registers the HSET command with the CommandRegistry during package initialization.

(h SSMap) Get(k string) (string, bool) Function​

func (h SSMap) Get(k string) (string, bool) {
	value, ok := h[k]
	if !ok {
		return "", false
	}
	return value, true
}
  • Purpose: Retrieves the value associated with a given key from the SSMap.
  • Parameters:
    • k string: The key to retrieve.
  • Returns:
    • string: The value associated with the key. Returns an empty string if the key is not found.
    • bool: Indicates whether the key was found in the map.

(h SSMap) Set(k, v string) (string, bool) Function​

func (h SSMap) Set(k, v string) (string, bool) {
	value, ok := h[k]
	if ok {
		oldValue := value
		h[k] = v
		return oldValue, true
	}

	h[k] = v
	return "", false
}
  • Purpose: Sets the value for a given key in the SSMap.
  • Parameters:
    • k string: The key to set.
    • v string: The value to associate with the key.
  • Returns:
    • string: The old value associated with the key, if it existed. Returns an empty string if the key was not previously present.
    • bool: Indicates whether the key was already present in the map.

evalHSET(c *Cmd, s *dstore.Store) (*CmdRes, error) Function​

func evalHSET(c *Cmd, s *dstore.Store) (*CmdRes, error) {
	key := c.C.Args[0]

	var m SSMap
	var newFields int64

	obj := s.Get(key)
	if obj != nil {
		if err := object.AssertType(obj.Type, object.ObjTypeSSMap); err != nil {
			return cmdResNil, errors.ErrWrongTypeOperation
		}
		m = obj.Value.(SSMap)
	} else {
		m = make(SSMap)
	}

	// kvs is the list of key-value pairs to set in the SSMap
	// key and value are alternating elements in the list
	kvs := c.C.Args[1:]
	if (len(kvs) & 1) == 1 {
		return cmdResNil, errors.ErrWrongArgumentCount("HSET")
	}

	for i := 0; i < len(kvs); i += 2 {
		k, v := kvs[i], kvs[i+1]
		if _, ok := m[k]; !ok {
			newFields++
		}
		m[k] = v
	}

	obj = s.NewObj(m, -1, object.ObjTypeSSMap)
	s.Put(key, obj)

	return cmdResInt(newFields), nil
}
  • Purpose: Evaluates the HSET command, setting field-value pairs in the SSMap stored at the given key.
  • Parameters:
    • c *Cmd: The command to evaluate.
    • s *dstore.Store: The data store.
  • Returns:
    • *CmdRes: The result of the command, indicating the number of new fields added.
    • error: An error if one occurred, such as an incorrect argument count or type.

executeHSET(c *Cmd, sm *shardmanager.ShardManager) (*CmdRes, error) Function​

func executeHSET(c *Cmd, sm *shardmanager.ShardManager) (*CmdRes, error) {
	if len(c.C.Args) < 3 {
		return cmdResNil, errors.ErrWrongArgumentCount("HSET")
	}
	shard := sm.GetShardForKey(c.C.Args[0])
	return evalHSET(c, shard.Thread.Store())
}
  • Purpose: Executes the HSET command by retrieving the appropriate shard and calling evalHSET.
  • Parameters:
    • c *Cmd: The command to execute.
    • sm *shardmanager.ShardManager: The shard manager.
  • Returns:
    • *CmdRes: The result of the command.
    • error: An error if one occurred, such as an incorrect argument count.

Code Examples​

None.

Getting Started Relevance​