18.2. Adding THEN actions in DRL rules

The then part of the rule contains the actions to be performed when the conditional part of the rule has been met. For example, when a loan applicant is under 21 years old, the then action of an "Underage" rule would be setApproved( false ), declining the loan because the applicant is under age. Actions consist of one or more methods that execute consequences based on the rule conditions and on available data objects in the package. The main purpose of rule actions is to to insert, delete, or modify data in the working memory of the decision engine.

Prerequisites

  • The package is defined at the top of the DRL file. This should have been done for you when you created the file.
  • The import list of data objects used in the rule is defined below the package line of the DRL file. Data objects can be from this package or from another package in Business Central.
  • The rule name is defined in the format rule "name" below the package, import, and other lines that apply to the entire DRL file. The same rule name cannot be used more than once in the same package. Optional rule attributes (such as salience or no-loop) that define rule behavior are below the rule name, before the when section.

Procedure

  1. In the DRL designer, enter then after the when section of the rule to begin adding action statements.

  2. Enter one or more actions to be executed on fact patterns based on the conditions for the rule.

    The following are some of the keyword options for defining DRL actions:

    • set: Use this to set the value of a field. 

      $application.setApproved ( false );
$application.setExplanation( "has been bankrupt" );

    • modify: Use this to specify fields to be modified for a fact and to notify the decision engine of the change. This method provides a structured approach to fact updates. It combines the update operation with setter calls to change object fields. 

      modify( LoanApplication ) {
        setAmount( 100 ),
        setApproved ( true )
}

    • update: Use this to specify fields and the entire related fact to be updated and to notify the decision engine of the change. After a fact has changed, you must call update before changing another fact that might be affected by the updated values. To avoid this added step, use the modify method instead. 

      LoanApplication.setAmount( 100 );
update( LoanApplication );

    • insert: Use this to insert a new fact into the decision engine. 

      insert( new Applicant() );

    • insertLogical: Use this to insert a new fact logically into the decision engine. The decision engine is responsible for logical decisions on insertions and retractions of facts. After regular or stated insertions, facts must be retracted explicitly. After logical insertions, the facts that were inserted are automatically retracted when the conditions in the rules that inserted the facts are no longer true. 

      insertLogical( new Applicant() );

    • delete: Use this to remove an object from the decision engine. The keyword retract is also supported in DRL and executes the same action, but delete is typically preferred in DRL code for consistency with the keyword insert. 

      delete( Applicant );
    注記

    For more information about DRL rule actions, see 「Rule actions in DRL (THEN)」.

  3. After you define all action components of the rule, click Validate in the upper-right toolbar of the DRL designer to validate the DRL file. If the file validation fails, address any problems described in the error message, review all syntax and components in the DRL file, and try again to validate the file until the file passes.
  4. Click Save in the DRL designer to save your work.