82 lines
2.9 KiB
Markdown
82 lines
2.9 KiB
Markdown
---
|
|
layout: documentation
|
|
title: Rules Blockly - Value Storage
|
|
---
|
|
<!-- markdownlint-disable MD036 -->
|
|
|
|
# Value Storage
|
|
|
|
[return to Blockly Reference](index.html#value-storage)
|
|
|
|
## 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
|
|
|
|
[[toc]]
|
|
|
|
## Overview of the Value Storage blocks
|
|
|
|
|
|
|
|
### Caching
|
|
|
|
Since openHAB 4.0 caching functionality was introduced (provided that the rule is using [GraalJS / JS Scripting](/docs/configuration/blockly/#openhab-3-openhab-4-migration)).
|
|
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  [Global Value Storage](https://youtu.be/KwhYKy1_qVk?t=2060)
|
|
|
|
### Store Value
|
|
|
|
openHAB 4.0
|
|
|
|
|
|
|
|
|
|
Function: Stores a value under the key name in the specified [cache](#caching).
|
|
|
|
### Get Stored Value
|
|
|
|
Since openHAB 4.0:
|
|
|
|
|
|
|
|
|
|
|
|
Function: Retrieves a stored value by the key name from the specified [cache](#caching).
|
|
|
|
### Check if Value is undefined
|
|
|
|
Since openHAB 4.0:
|
|
|
|
|
|
|
|
|
|
|
|
Function: Checks if a value is undefined in the specified [cache](#caching)
|
|
|
|
### 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
|
|
|
|
[return to Blockly Reference](index.html#value-storage)
|