Question

I am writing an object conversion class, used to convert domain layer objects into UI objects and vice versa. The problem is that my UI objects are organized into a hierarchy and as a result my object conversion class contains “instanceof” statements. There is a definite code smell here but I’m not sure what the solution is.

So my UI hierarchy contains a RuleDTO as follows:

public class RuleDTO {
    protected long ruleID;
    protected long rowID;   
    protected AttributeDTO leftCondition;
    protected AttributeDTO rightCondition;
    protected OperationTypeDTO operationType; 
    protected boolean isActive;     
    // etc...
}

My RuleDTO can then be subclassed by AssignmentRuleDTO as follows:

public class AssignmentRuleDTO extends RuleDTO {
    protected String assignedToTeam;
    protected String assignmentOperator;        
    // etc...
}

RuleDTO can also be subclassed by EvaluationRuleDTO:

public class EvaluationRuleDTO extends RuleDTO {
    protected String successAction;
    protected String failureAction;
    // etc...
}

The problem is reached then in my ObjectConversionHelper class which contains the following type of logic:

{
    // Perform logic common to RuleDTO such as setting ruleID, isActive etc
    if(ruleDTO instanceof AssignmentRuleDTO) {
        // Set assignedToTeam and assignmentOperator etc
    }
    else if (ruleDTO instanceOf EvaluationRuleDTO) {
        // Set successAction and failureAction etc  
    }
}

What would be a good solution here instead? I’ve read about the visitor pattern, but not sure how it applies here.

Thanks

Answer 1

Your RuleDTO class should have a method called setStuff() or something similar.

Then you override it in AssignmentRuleDTO and in EvaluationRuleDTO to set the relevant fields.

This way your ObjectConversionHelper can just call

ruleDTO.setStuff();