We've seen, so far, the simplest cases to check attribute values against the boolean expressions in our rules. We've also discussed all the different ways in which rules can manage data updates, which might retrigger checking our rules. However, the power of rules doesn't stop there as there are many different ways in which the rule conditions can be written, which will allow us to create rules that are both powerful and simple to understand.
Drools already provides a set of operations that you can use to compare different objects against each other. These objects might be living directly on the working memory, global variables, literal values, or any combination of these types. We're going to enumerate the most used ones in the following sections, splitting them into the following:
Boolean and numeric operations
Collection-based operations
Regex operations
Custom operations