# Perspective Tag Expression Binding can't be dynamic?

**URL:** <https://forum.inductiveautomation.com/t/perspective-tag-expression-binding-cant-be-dynamic/77953>\
**Category:** Ignition\
**Tags:** perspective\
**Created:** [August 16, 2023, 6:57pm UTC](https://forum.inductiveautomation.com/t/perspective-tag-expression-binding-cant-be-dynamic/77953 "2023-08-16T18:57:35Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Alexandre\_Pasquereau](https://avatars.discourse-cdn.com/v4/letter/a/9e8a1a/32.png) [@Alexandre\_Pasquereau](https://forum.inductiveautomation.com/u/Alexandre_Pasquereau)\
**Post date:** [August 16, 2023, 6:57pm UTC](https://forum.inductiveautomation.com/t/perspective-tag-expression-binding-cant-be-dynamic/77953/1 "2023-08-16T18:57:35Z")

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Hi,

I'm trying to configure a dynamic binding in Perspective. I created one using an Expression binding type and it's working, but I want to be able to modify the value of the tag that returns the expression (so I want it bidirectional). Then I saw that in the Tag binding type we can put an expression, and I thought that the Bidirectional option would solve my problem, but when I copy pasted the expression in the Tag binding type I had an Error\_Configuration and it's not working, I don't know why.

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/f/f/ff28c777961cc86f02d8d11de057e8dc9067ae32.png)

For the Expression type I have a "Bad\_NotFound" which is normal because it's a dynamic expression and she doesn't have the values of the parameters but it's working well when I launch Perspective, I have the good values.

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/1/1/11d4ec233905f9cec1cf9439bb7e8c9fbd2c1ae0.png)

But here, for the Tag type I have "Error\_Configuration", and an error when I launch Perspective.  
So I'm thinking, we can't have dynamic Tag binding with an expression ?

Here's the expression:

```auto
if(indexof({this.meta.name},"uplimit") != -1, tag("[default]BatchInformation/Limits/"+tag("[default]BatchInformation/Mill"+{view.params.Mill}+"/Status/Product Type")+"/"+{view.params.Stage}+"/up/"+{parent.meta.name}), 
if(indexof({this.meta.name},"lwlimit") != -1, tag("[default]BatchInformation/Limits/"+tag("[default]BatchInformation/Mill"+{view.params.Mill}+"/Status/Product Type")+"/"+{view.params.Stage}+"/lw/"+{parent.meta.name}),
if(indexof({this.meta.name},"limit") != -1, tag("[default]BatchInformation/Limits/"+tag("[default]BatchInformation/Mill"+{view.params.Mill}+"/Status/Product Type")+"/"+{view.params.Stage}+"/Limit/"+{parent.meta.name}), None)))

```

Thanks

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<div class="post-metadata">

**Author:** ![paul-griffith](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/paul-griffith/32/37249_2.png) [@paul-griffith](https://forum.inductiveautomation.com/u/paul-griffith)\
**Post date:** [August 16, 2023, 7:14pm UTC](https://forum.inductiveautomation.com/t/perspective-tag-expression-binding-cant-be-dynamic/77953/2 "2023-08-16T19:14:06Z")

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A tag binding in 'expression' mode runs an expression that is **required to return a tag path**.  
[https://docs.inductiveautomation.com/display/DOC81/Tag+Bindings+in+Perspective#TagBindingsinPerspective-TagExpressionBinding](https://docs.inductiveautomation.com/display/DOC81/Tag+Bindings+in+Perspective#TagBindingsinPerspective-TagExpressionBinding)

It's an indirect tag binding that's able to run logic. You should not ever need to use the `tag()` function (in general, but especially) in a tag binding configured for expression mode. Simply assemble whatever literal strings or, possibly, dynamic references (using standard curly brace tag reference lookup for an expression) into a single desired tag path.

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<div class="post-metadata">

**Author:** ![Alexandre\_Pasquereau](https://avatars.discourse-cdn.com/v4/letter/a/9e8a1a/32.png) [@Alexandre\_Pasquereau](https://forum.inductiveautomation.com/u/Alexandre_Pasquereau)\
**Post date:** [August 16, 2023, 7:16pm UTC](https://forum.inductiveautomation.com/t/perspective-tag-expression-binding-cant-be-dynamic/77953/3 "2023-08-16T19:16:06Z")

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Oh yes makes sense, I'm returning the value so of course it's not working, thanks!