90 lines
4.4 KiB
Markdown
90 lines
4.4 KiB
Markdown
---
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layout: documentation
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title: Rules Blockly - Persistence
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---
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<!-- markdownlint-disable MD036 -->
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# Persistence
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[return to Blockly Reference](index.html#persistence)
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## Introduction
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Persistence blocks enable access to and manipulation of historical data stored by the default persistence service.
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For more information on persistence, the default service, and its configuration see the [persistence documentation](https://www.openhab.org/docs/configuration/persistence.html).
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The date-blocks shown in this section are described previously in [Date handling blocks](https://community.openhab.org/t/blockly-reference/128785#date-handling-blocks-31).
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[[toc]]
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## Overview of the Persistence blocks
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## Persistence Blocks
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Persistence blocks enable access of historical data stored by the default persistence service.
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For more information on persistence, the default service, and its configuration see the [persistence documentation](https://www.openhab.org/docs/configuration/persistence.html).
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The date-blocks shown in this section are described previously in [Date handling blocks](https://community.openhab.org/t/blockly-reference/128785#date-handling-blocks-31).
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More about that topic can be viewed at  [Using Persistence data](https://youtu.be/KwhYKy1_qVk?t=1440)
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### Get statistical value of an item
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_Function:_ computes any of the below functions for the given item since the time provided by _ZonedDateTime_-Block
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- average: gets the average value of the State of a persisted Item since a certain point in time.
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This method uses a time-weighted average calculation
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- delta: gets the difference in value of the State of a given Item since a certain point in time
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- deviation: gets the standard deviation of the state of the given Item since a certain point in time
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- variance: gets the variance of the state of the given item since a certain point in time
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- evolution rate: gets the evolution rate of the state of the given Item in percent since a certain point in time (may be positive or negative)
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- minimum: gets the minimum value of the State of the given Item since a certain point in time
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- maximum: gets the maximum value of the State of the given Item since a certain point in time
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- sum: gets the sum of the State of the given Item since a certain point in time
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- historic state: gets the historic state at a certain point in time
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In the case of the following two functions the block changes its appearance by replacing the time with an option to chose if the equal value should be skipped or not:
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- previous state value: Gets the previous state with option to skip to different value as current
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- previous state numeric value: same as above but directly returns a number without a unit
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- previous state value time: Gets the time when previous state last occurred with option to skip to different value as current
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The persistence dropdown allows to select the persistence storage from which the value should be retrieved.
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It automatically shows only the storage types that are currently installed on your openHAB instance.
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Note that not all persistence storage types (i.e. the default rrd4j) support all statistical methods.
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The **skip option** set to true allows to search for first state that is different from the current state.
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_Important:_ This option is not supported by all persistence databases and may throw an error in that case (for example the standard rrd4j does _not_ support it while influxdb does support it).
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Notes: in case no or 0 values are retrieved, make sure that the item in question is actually persisted.
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**Previous State Example**
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### Check item change / update since a point in time
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_Function:_ checks if an item was updated or changed since a certain point in time
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Type: boolean `true` or `false`
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### Provide last updated date of an Item
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_Function:_ Provides the last updated date (including time) of an Item
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Type: ZonedDateTime
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## Return to Blockly Reference
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[return to Blockly Reference](index.html#persistence)
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