cmd_getset.go

cmd_getset.go - Overview

This file defines the GETSET command, which sets the value of a key and returns its old value.

Detailed Documentation

cGETSET

var cGETSET = &CommandMeta{
	Name:      "GETSET",
	Syntax:    "GETSET key value",
	HelpShort: "GETSET sets the value for the key and returns the old value",
	HelpLong: `
GETSET sets the value for the key and returns the old value.

The command returns (nil) if the key does not exist.
	`,
	Examples: `
localhost:7379> SET k1 v1
OK OK
localhost:7379> GETSET k1 v2
OK v1
localhost:7379> GET k1
OK v2
	`,
	Eval:    evalGETSET,
	Execute: executeGETSET,
}

• Purpose: Defines the metadata for the GETSET command, including its name, syntax, help text, examples, and the functions to evaluate and execute the command.
• Fields:
  • Name: The name of the command ("GETSET").
  • Syntax: The command's syntax ("GETSET key value").
  • HelpShort: A short description of the command.
  • HelpLong: A longer, more detailed description of the command.
  • Examples: Example usages of the command.
  • Eval: The function (evalGETSET) responsible for evaluating the command.
  • Execute: The function (executeGETSET) responsible for executing the command.

init

func init() {
	CommandRegistry.AddCommand(cGETSET)
}

• Purpose: Registers the GETSET command with the CommandRegistry.
• Details: This function is automatically called when the package is initialized. It adds the cGETSET command to the global CommandRegistry, making it available for use.

evalGETSET

func evalGETSET(c *Cmd, s *dstore.Store) (*CmdRes, error) {
	if len(c.C.Args) != 2 {
		return cmdResNil, errors.ErrWrongArgumentCount("GETSET")
	}
	key, value := c.C.Args[0], c.C.Args[1]
	obj := s.Get(key)

	// Put the new value in the store
	s.Put(key, CreateObjectFromValue(s, value, -1))

	// Return the old value, if the key does not exist, return nil
	if obj == nil {
		return cmdResNil, nil
	}

	// Return the old value
	return cmdResFromObject(obj)
}

• Purpose: Evaluates the GETSET command, setting the value for the key and returning the old value.
• Parameters:
  • c: A pointer to the Cmd struct representing the command.
  • s: A pointer to the dstore.Store struct representing the data store.
• Returns:
  • *CmdRes: A pointer to the CmdRes struct representing the command result.
  • error: An error if one occurred, or nil if the command was successful.
• Details:
  • It checks if the number of arguments is correct (2).
  • It retrieves the key and value from the command arguments.
  • It gets the old object from the store using the key.
  • It puts the new value into the store.
  • It returns the old value (or nil if the key did not exist).

executeGETSET

func executeGETSET(c *Cmd, sm *shardmanager.ShardManager) (*CmdRes, error) {
	if len(c.C.Args) != 2 {
		return cmdResNil, errors.ErrWrongArgumentCount("GETSET")
	}
	shard := sm.GetShardForKey(c.C.Args[0])
	return evalGETSET(c, shard.Thread.Store())
}

• Purpose: Executes the GETSET command on the appropriate shard.
• Parameters:
  • c: A pointer to the Cmd struct representing the command.
  • sm: A pointer to the shardmanager.ShardManager struct.
• Returns:
  • *CmdRes: A pointer to the CmdRes struct representing the command result.
  • error: An error if one occurred, or nil if the command was successful.
• Details:
  • It checks if the number of arguments is correct (2).
  • It gets the shard for the key from the ShardManager.
  • It calls evalGETSET with the command and the shard's store.

Getting Started Relevance