Design Pattern: Unbound Item (aka Virtual Item)

[rlkoshak]

Design Pattern: What is a Design Pattern and How Do I Use Them

What Is a Design Pattern (DP) an approach to solving a common set of problems in Rules in a standard way generic and applicable to multiple specific problems, not just the example implementations that are included in the article intended to work together, i.e. multiple design patterns can and should be used to solve one problem What a Design Pattern Is Not a complete solution: DPs are not comprehensive in scope; they are intended to be part of a solution, not a complete solution. There will b…

Problem Statement

Sometimes one needs to create a flag, control, switch, or some other control that is not bound to a device or channel. For example, a Switch to override presence detection.

Concept

Create an Item that does not have a binding configuration.

Simple Example

Switch VirtualItem "label" <icon> (groups) // No binding config

See the Sensor Aggregation Design Pattern for a more complicated example. The Virtual Item is Override_Presence in that example.

Advantages and Limitations

Virtual Items are a good way to store state needed by rules and to provide a way to allow the user to modify the behavior of their rules by adjusting parameters stored in Virtual Items. Data stored in Virtual Items can also be persisted and restored on startup unlike global vars and vals.

Related Design Patterns

• Proxy Item: A Proxy Item is a special case for Virtual Items
• Sensor Aggregation: Override_Presence is a Virtual Item
• TimeOfDay: the TimeOfDay Item is a Virtual Item
• Separation of Behaviors: Uses a Virtual Item as the means to trigger the rules where the cross cutting logic is executed

[yves]

Data stored in Virtual Items can also be persisted and restored on startup unlike global vars and vals.

You might want to add how to do that.

I have figured out, by adding it to a group that was persisted and that group had restoreOnStartup in the .persiste file.

Yet it took me a long time to find that.