Is the extended tag path format for history queries documented?

Ignition
1

I was doing some hackish things with a history DB, and landed in a situation where I could no longer see the history for one specific tag using system.tag.queryTagHistory. Just to make sure I wasn't fumbling a parameter, I tried a history binding in Perspective for the same tag and it worked.

Then I noticed that the designer UI had built the tag path in a form I've never seen documented. I tried that path with queryTagHistory and it got data.

I was using a more simple:

my_hist = system.tag.queryTagHistory(['[default]some_folder/foo'])

And the designer UI came up with this tag path:

my_hist = system.tag.queryTagHistory(['[db_name/gateway_name:default]some_folder/foo'])

I get why this longer form could be necessary and even why I needed it in my case. I'm just here to complain that I've never seen this form of tag path documented anywhere. The manual page for queryTagHistory doesn't mention it, nor does the manual page it links to specifically about tag paths. It's also not like the special history paths mentioned in the historian docs.

Is this format somewhere else in the manual? Should it be? Is it "safe" to use or likely to break in a future update?

2

Brief description here:

The form you show is how you use Ignition's TagPath objects to escape the implicit history provider defaults for a given tag provider. The "long form" linked is what you get when using Ignition's more modern QualifiedPath objects.

Note that db_name should really be hist_prov_name, as it could be a 3rd party historian.

And yeah, the docs are terrible on this subject.

1 Like
3

Just confirming my misbehaving tag also works fine when I query like this:

my_hist = system.tag.queryTagHistory(['histprov:db_name:/drv:gateway_name:default:/tag:some_folder/foo'])

Still using db_name so it matches my earlier example, although I see how it more accurately is a history provider name...