# deriveExpressionGetter and deriveExpressionSetter

**URL:** <https://forum.inductiveautomation.com/t/deriveexpressiongetter-and-deriveexpressionsetter/113023>\
**Category:** Ignition\
**Created:** [December 30, 2025, 1:25pm UTC](https://forum.inductiveautomation.com/t/deriveexpressiongetter-and-deriveexpressionsetter/113023 "2025-12-30T13:25:11Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![akivabrookler](https://avatars.discourse-cdn.com/v4/letter/a/41988e/32.png) [@akivabrookler](https://forum.inductiveautomation.com/u/akivabrookler)\
**Post date:** [December 30, 2025, 1:25pm UTC](https://forum.inductiveautomation.com/t/deriveexpressiongetter-and-deriveexpressionsetter/113023/1 "2025-12-30T13:25:11Z")

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Where are `deriveExpressionGetter` and `deriveExpressionSetter` used within Ignition?

They are mentioned in the docs as “JSON/Scripting Name” but tag export JSON files use `readExpression` and `writeExpression` instead. The `tagconfig` table also seems to use this format.

> **[Tag Properties | Ignition User Manual](https://www.docs.inductiveautomation.com/docs/8.3/platform/tags/tag-properties)**
>
> Tags are points of data and may have static values or dynamic values that come from an OPC address, an Expression, or a SQL query. The values can be used on screens and in Transaction Groups. Additionally, tags offer a core set of features above and...

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [December 30, 2025, 1:42pm UTC](https://forum.inductiveautomation.com/t/deriveexpressiongetter-and-deriveexpressionsetter/113023/2 "2025-12-30T13:42:39Z")

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Should be the getter and setter expressions on derived tags?

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<div class="post-metadata">

**Author:** ![Leor\_Fishman](https://avatars.discourse-cdn.com/v4/letter/l/e19adc/32.png) [@Leor\_Fishman](https://forum.inductiveautomation.com/u/Leor_Fishman)\
**Post date:** [December 30, 2025, 6:35pm UTC](https://forum.inductiveautomation.com/t/deriveexpressiongetter-and-deriveexpressionsetter/113023/3 "2025-12-30T18:35:46Z")

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What’s confusing is that those also seem to be called readExpression and writeExpression in e.g. tag export

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**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [December 30, 2025, 7:11pm UTC](https://forum.inductiveautomation.com/t/deriveexpressiongetter-and-deriveexpressionsetter/113023/4 "2025-12-30T19:11:01Z")

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Hmm. Some backwards compatibility override somewhere?

This in the script console:

```python
from com.inductiveautomation.ignition.common.tags.config.types import ReferenceTagTypeProps
prop = ReferenceTagTypeProps.DeriveExpressionGetter
print prop.name
print prop.description
print prop.category
print prop.defaultValue
print prop.clazz

```

Yields:

```python
>>> 
deriveExpressionGetter
The expression that determines how the value on the Derived Tag is displayed.
Value
{source}
<type 'java.lang.String'>
>>>

```

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<div class="post-metadata">

**Author:** ![akivabrookler](https://avatars.discourse-cdn.com/v4/letter/a/41988e/32.png) [@akivabrookler](https://forum.inductiveautomation.com/u/akivabrookler)\
**Post date:** [December 30, 2025, 7:28pm UTC](https://forum.inductiveautomation.com/t/deriveexpressiongetter-and-deriveexpressionsetter/113023/5 "2025-12-30T19:28:18Z")

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![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/a/5/a5f26281b91c2d161ee84ebba284b9de52ef322e.png)