Chained variables

Chained variables, also called linked variables or nested variables, are query variables with one or more other variables in their variable query. This page explains how chained variables work and provides links to example dashboards that use chained variables.

Chained variable queries are different for every data source, but the premise is the same for all. You can use chained variable queries in any data source that allows them.

Extremely complex linked templated dashboards are possible, 5 or 10 levels deep. Technically, there is no limit to how deep or complex you can go, but the more links you have, the greater the query load.

The following practices will make your dashboards and variables easier to use.

• Chaining variables create parent/child dependencies. You can envision them as a ladder or a tree.
• The easiest way to create a new chained variable is to copy the variable that you want to base the new one on. In the variable list, click the Duplicate variable icon to the right of the variable entry to create a copy. You can then add on to the query for the parent variable.
• New variables created this way appear at the bottom of the list. You might need to drag it to a different position in the list to get it into a logical order.

You can change the orders of variables in the dashboard variable list by clicking the up and down arrows on the right side of each entry. DranSCADA lists variable dropdowns left to right according to this list, with the variable at the top on the far left.

• List variables that do not have dependencies at the top, before their child variables.
• Each variable should follow the one it is dependent on.
• Remember there is no indication in the UI of which variables have dependency relationships. List the variables in a logical order to make it easy on other users (and yourself).

The more layers of dependency you have in variables, the longer it will take to update dashboards after you change variables.

For example, if you have a series of four linked variables (country, region, server, metric) and you change a root variable value (country), then DranSCADA must run queries for all the dependent variables before it updates the visualizations in the dashboard.