Cool way to dynamically add entries to a list on create in grails

Hi all

A good friend had problem recently with adding items to list opon first create in grails. The problem is how can you set the property of an item as position x in a list if it does not yet exist at that position. Well will with a little magic and grails we did this.

The answer is Lazylist and Lazymap implementations from the commons collection package. So we end up with this result.

import org.apache.commons.collections.Factory;
import org.apache.commons.collections.ListUtils;

public class Requirement {

    String label;
    List requirements = 
    new ListUtils.lazyList(new ArrayList(),{new Requirement()} as Factory)

    static hasMany = [requirements:Requirement];


    static constraints = {
        label(blank:false);
    }
        
}

This means in your create form page you can have an entry like this:

<g:textField name="requirements[${i}].label" value=""/>

When you create a Requirement object like this in the controller action.

Requirement r = new Requirement(params)

The new entries will be created in the collection and the label value on them set. The same thing can be done with LazyMap.

enjoy :)