I followed a tutorial on Drools and implemented the same thing. I`m trying to figure out what means I can use to change the values in the .drl file through the frontend. Below is the Drools file I used, called order.drl. Domain-specific languages (or DSLs) are a way to create a rule language dedicated to your problem domain. A set of DSL definitions consists of transformations from DSL „sets“ to DRL constructs that allow you to use all the underlying rule language and module functions. With a DSL, you write rules to DSL rules files (or DSLR files) that are translated into DRL files. Import statements work like import statements in Java. You must specify full paths and type names for all objects that you want to use in the rules. Drools automatically imports classes from the Java package of the same name and also from the java.lang package. We can use salience to define the order of fire rules.
Salience has an attribute that takes any expression that returns a certain number of int types (positive and negative numbers are valid). The higher the value, the more likely it is that a rule will be taken over by the conflict resolution strategy to be drawn. Examples of poorly and properly used rules The next screen will ask you to select some files that you want to have in your first Drools project. In this example, People is a source of Person facts. A rule unit data source is a data source processed by a particular control unit and represents the entry point that the decision module uses to evaluate the control unit. The global variable adultAge is accessible from all rules belonging to this control unit. The last two methods are part of the life cycle of the control unit and are called by the decision module. Drools includes utility classes for transformation between formats. This works by analyzing the rules of the source format in the AST and then „dropping“ them into the appropriate target format. For example, this allows you to write rules to DRL and export them to XML if needed in the future. As you have seen, the .drl file (rules) has its own syntax, let`s cover some of the syntax of the rules in this chapter.
Each rule must have a unique name in the rule package. If you use the same rule name multiple times in a .drl file in the package, the rules cannot be compiled. Always enclose rule names in double quotation marks (rule rule) to avoid possible compilation errors, especially if you use spaces in rule names. Other scenarios in which you want to use XML are if you have a tool that generates rules from one input (programmatically generated rules), or perhaps from another rule language, or another tool that generates XML (XSLT makes it easier to transform between XML formats). Note that you can still generate a normal day. The decision table is grouped into different sections, the top one is like a header section where we specify the RuleSet (i.e. the package that contains the rules files), Import (Java classes to import) and Notes (comments for rules purposes). Declared types are typically used in rules files, while Java templates are used when the model is shared between rules and applications. However, the application sometimes needs to access and process the facts of the declared types, especially if it encapsulates the rules engine and provides top-level domain-specific user interfaces for policy management.
You can also embed Drools in a product that already uses XML for configuration, so you want the rules to be in xml format. You may be creating your own rules language on XML – note that you can still use AST objects directly to create your own rules language (the options are varied due to the open architecture). Each rule has an integer salience attribute that is set to zero by default and can be negative or positive. Salience is a form of priority in which rules with higher salience values receive a higher priority when placed in the activation queue. Type declarations have two main purposes in the rules engine: declaring new types and declaring metadata for types. Then add the import statement to the DRL file to call the writeHello method from the DRL file. The following code block highlights the changes made to the DrL Pune.drl file in yellow. Using accumulate with custom online code is not a good practice for several reasons, including the difficulty in maintaining and testing the rules they use, as well as the inability to reuse that code.
Implementing your own cumulative features is very simple and straightforward, they are easy to test and use. This form of rollup is supported only for backward compatibility. The order in which the items are declared is not important, except for the package name, which, when declared, must be the first item in the rules file. All elements are optional, so you only use the elements you need. We will discuss each of them in the following sections. The buildAll() method called on KieBuilder creates all the resources and binds them to KieBase. It only works properly if it is able to find and validate all rule files: Although the decision engine supports other formats for the accumulate element for backward compatibility, this format is preferred for optimal performance in rules and applications. You can run a rule unit in passive mode using the run() method (equivalent to calling fireAllRules() in a KIE session) or in active mode using the runUntilHalt() method (equivalent to calling fireUntilHalt() in a KIE session). By default, the decision engine runs in passive mode and evaluates rule units only when a user or application explicitly calls run() (or fireAllRules() for default rules). When a user or application calls runUntilHalt() for rule units (or fireUntilHalt() for default rules, the decision engine starts in active mode and continuously evaluates the rule units until the user or application explicitly calls halt().
Example of DRL rules with controlled execution with drools.run() Use the following format to define the cumulation conditions in the rules: You can then use the class generated in your rules as any other fact, as shown in the previous example rule with the person type declaration: For Pune and Nagpur, if the element is a drug, the local tax is zero. If the item is a food product, the tax is depending on the city. Additional rules can be added to DRL files for other products. This is just one example of a program. The second solution is to use rule templates (link to the Drools documentation). The basic idea is that you provide a data table and model for a DRL, and the Drools framework creates the data for the model and generates the DRLs for you. This is useful if you have very repetitive rules like yours – where others essentially apply the same rule with different restrictions. The operator returns true if the string does not match the regular expression. The same rules apply as for the match operator.
For example, after you apply the breakpoints, you must debug your app as a Drools app. Drools breakpoints (breakpoints in the DRL file) only work if your application is debugged as a Drools application. To do the same — A string that identifies an activation group (or XOR group) to which you want to assign the rule. Only one rule can be activated in activation groups.