Historizing a large JSON string tag

Ignition
,
1

Hi all,

I have a problem storing data from a tag containing a JSON string (or Python dictionary, if you will) within Ignition. Generally, the string exceeds the VARCHAR(255) character limit that is implemented in the tag historian tables (stringvalue column). Thus, a MySQL table cannot accept the value and refuses to historize it, causing the values to aggregate in store and forward.

I also cannot automate an alteration of that table column to VARCHAR(8191) or whatever, since tables are partitioned by day and millions of rows are being stored - tables that already exist are difficult to modify without errors, this may be unreliable.

Anyone have a good, alternative solution to this? Breaking the JSON string up into multiple columns? Turning the data into tags?

Best Regards,
Roger

2

You could probably create an expression tag which you can use to break up the string. Using the split function in the Expression editor, you can convert it into a dataset and extract the data you need from there. This is assuming the data in JSON format was converted into a string before hand.

Split function: https://docs.inductiveautomation.com/display/DOC/split

3

You can turn the data into tags using the jsonGet expression function.