# Value Storage

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# Introduction

These blocks enable storing information for a rule that is kept after the rule has run, so it can be reused when the rule is run again later in stateful way. Basically a value storage can be perceived as a global variable for the rule instance.

  • The values are persisted as a part of the instance of the rule
    • Modifying the rule during development creates a new instance which means the value is reset.
    • Restarting openHAB creates a new rule instance which also means the value is reset
    • In most cases both situations are negligible for many rules.
  • If you need full persistence of values that can be used across rules you need to persist the value in one of the persistence engines like MapDB
  • By default the value is undefined. To check if a value is undefined, use the special "is undefined"-block

# Overview of the Value Storage blocks


# Caching

Since openHAB 4.0 caching functionality was introduced (provided that the rule is using GraalJS / JS Scripting). The blocks have the same behaviour like before when set to "private cache" which means that the value is stores in the rule cache. When storing a value in the "shared cache" the value can be even used beyond the specific rule in a different rule.


# Value Storage Blocks

See also the short video part about youtube Global Value Storage (opens new window)

# Store Value

openHAB 4.0 store-value-cache


Function: Stores a value under the key name in the specified cache.

# Get Stored Value

Since openHAB 4.0:



Function: Retrieves a stored value by the key name from the specified cache.

# Check if Value is undefined

Since openHAB 4.0:



Function: Checks if a value is undefined in the specified cache

# Example 1: Initialize a key if not set


# Example 2: Use the rule instance variable to remember a color that has been set


# Return to Blockly Reference

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