How to Update Non Polling Expression Client Tag

Ignition
1

I have a client tag that is a datset based on a SQL query. If I set the Polling Mode to Off, how can I get the tag to update its value when the data in the database table changes?

2

You would have to read the data in the database somehow to know when you needed to update the dataset, so I don’t think you can do this automatically without polling. You can trigger the update manually off a button press if that would work.

3

That would indeed work. By what mechanism would I do that? :slight_smile:

4

You can do this one of 2 ways: binding or scripting.

Binding

  1. Create a Client tag called ‘trigger’ with Data Type Boolean.
  2. Create a client tag of Data Type DataSet. Set its Expression Type to SQL Query, its Polling Mode Off and the query to SELECT * FROM table WHERE {[~]trigger}={[~]trigger}
  3. Create a button and set its actionPerformed script to value = system.tag.read('[Client]trigger').value system.tag.writeToTag('[Client]trigger', not value)When you click the button, the value of the tag ‘trigger’ will be toggled. This will change the text inside the SQL Query from SELECT * FROM Table WHERE 0=0 to SELECT * FROM Table WHERE 1=1This won’t change the result of the query but will force it to be updated.

Scripting

  1. Create a Client tag of Data Type DataSet.
  2. Create a button and set its actionPerformed script to data = system.db.runQuery("SELECT * FROM table") system.tag.write("[Client]Scripting tag", system.dataset.toDataSet(data))When you press the button the query will be run and the tag updated with the result.
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