How ESQL expressions are used with While nodes and Switch nodes

Using an ESQL expression with a While node

The ESQL expression of a While node states the loop condition for the While loop to which the While node belongs.

To work properly a While node must contain an ESQL expression that resolves to a Boolean true or false value. At runtime the While node evaluates the ESQL expression and obtains a result. If the result is true then the While node invokes its associated flow. Otherwise the While node terminates (see Basic information about While nodes).

Using ESQL expressions with a Switch node

A Switch node has multiple output terminals (two or more) that are arranged vertically on the right side of the Switch node, as in the figure below:

Each output terminal has associated with it an ESQL expression that you must specify and that must evaluate to a Boolean value, either true or false. The last (bottommost) output terminal is the Default output terminal and is automatically associated with an ESQL expression that always evaluates to true.

To process the Switch node at runtime, the runtime code starts processing each output terminal in serial order starting with the topmost terminal. To process an output terminal, the runtime code evaluates the ESQL expression associated with the output terminal. If the ESQL expression evaluates to true, then the runtime code immediately stops processing output terminals and follows the flow branch connected to the output terminal whose ESQL expression evaluated to true.

If the runtime code reaches the Default output terminal (because the ESQL expressions associated with all the other output terminals returned false) then the runtime code evaluates the ESQL expression associated with the Default output terminal, finds that the result is true, and follows the flow branch connected to the output terminal.