Error writing value to a query tag

Ignition
1

Hi,
I have created a query tag reading value from a postgesSQL database.
I can read the value correctly with 1sec update time, but I cannot write value to the tag. Error shown below.

"Error writing “1” to tag [default]dbPlant/Devices/Light/cmd_manual Bad_ReadOnly(“Tag value source does not support writing.”

The tag value source is “db”.
Is it possible to write value to a query tag?

Thanks

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2

No. You must write to the DB yourself (scripted, using the system.db.* functions).

2 Likes
3

Thanks. I will tried it.

4

It works using the following script:
system.db.runUpdateQuery(“UPDATE device SET cmd_mode = ‘%s’ WHERE name = ‘%s’” % (queryValue, keyValue1), ‘dbPlant’)

5

I haven’t tested this, but I imagine this also works:

queryString = "UPDATE device SET cmd_mode=? WHERE name=?"
params = [queryValue,keyValue1]
system.db.runPrepUpdate(queryString,params,'dbPlant')

There’s a variety of reasons this is probably better than concatenating the query and values yourself including security (sql injection) and maybe performance (I think there might be a caching thing that runPrepUpdate takes advantage of). Even if I’m wrong about the performance part, it’s still good practice to use runPrepUpdate/runPrepQuery when needed instead of runQuery/runUpdateQuery for security.

1 Like