Play!> framework design pattern #1

A bad pattern is to handle different code to manage edition of items and creation of new items in the forms.

Typically you’ll pass an issue to the form when editing an existing one, and no one for the form to create new ones. Taking codeboard as an example, this would result in the following code in the controller and the template :

  • you don’t pass an issue object to the Play!> render method in newIssue() of the controller.
  • you pass an issue object to the render on issue() method (edition)
  • you handle behaviour of your form in the groovy template, particully managing default value which is not trivial for drop down list for example
    public static void newIssue(String identifier) {
            List<Tracker> trackers = Tracker.find("order by position asc").fetch();
            Project project = Project.find("identifier", identifier).first();
            List<User> users = User.find("order by login").fetch();
            List<State> states = State.find("order by position").fetch();
            List<Enumeration> priorities = Enumeration.find("byType", "IssuePriority").fetch();
            render("@issue", trackers, project, users, states, priorities);
    }

    public static void issue(Long id) {
            Issue issue = Issue.findById(id);
            Project project = issue.project;
            List<Tracker> trackers = Tracker.find("order by position asc").fetch();
            List<User> users = User.find("order by login").fetch();
            List<State> states = State.find("order by position").fetch();
            List<Enumeration> priorities = Enumeration.find("byType", "IssuePriority").fetch();
            render(issue, project, trackers, users, states, priorities);
           }

    #{if issue?.priority?.id}
    #{select 'priorityId', items:priorities, valueProperty:'id', labelProperty:'name', id:'priority', value:"${issue?.priority?.id}" /}
    #{/if}
    #{else}
    #{select 'priorityId', items:priorities, valueProperty:'id', labelProperty:'name', id:'priority', value:"2" /}
    #{/else}

This is not the better way to handle the form :

  • you have distinct code for edition and creation
  • you template handle default value (line 5 of the template sample code above), and the code is no more valid if you have an administration page to change default values (as it is possible in codebaord)

The good pattern is to create a new instance of the object in the model class :

  • the object will be passed to the form, thus not difference between edition and creation in forms
  • the model will handle default values or examples, which can be changed by administrators, and therefore be dynamic

The example below show the Issue model with management of default values that can be modified in others forms :

        public Issue(Project project) {
         this.project = project;
                this.state = State.find("isDefault = ?", true).first();

                this.priority = Enumeration.find("type = ? and is_default = ?", Enumeration.ISSUE_PRIORITY_TYPE, true).first();

        }

Now the difference between the method of creation and edition in the controller are just different by the initialisation of the issue object passed to the renderer :

  1. on edition, find the object by id (passed by the url)
  2. on creation, create a new issue
	public static void newIssue(String identifier) {
		Project project = Project.find("identifier", identifier).first();
		Issue issue = new Issue(project);
    	
		List<Tracker> trackers = Tracker.find("order by position asc").fetch();
		List<User> users = User.find("login <> 'root' order by login").fetch();
		List<State> states = State.find("order by position").fetch();
		List<Enumeration> priorities = Enumeration.find("byType", Enumeration.ISSUE_PRIORITY_TYPE).fetch();
		
		render("@issue", issue, trackers, users, states, priorities);
	}

    public static void editIssue(Long id) {
    	Issue issue = Issue.findById(id);

		List<Tracker> trackers = Tracker.find("order by position asc").fetch();
		List<User> users = User.find("login <> 'root' order by login").fetch();
		List<State> states = State.find("order by position").fetch();
		List<Enumeration> priorities = Enumeration.find("byType", Enumeration.ISSUE_PRIORITY_TYPE).fetch();
		
		render("@issue", issue, trackers, users, states, priorities);
    }

Then the code for the drop down list in groovy is just 1 line of code now !


#{select 'issue.priority.id', items:priorities, valueProperty:'id', labelProperty:'name', id:'priority', value:"${issue?.priority?.id}" /}
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