Build Menu from NavigableMap

Question

In a Grails 3.3 application, I'm trying to create a menu configuration and I'd like to use application.groovy for that.

application.groovy:

mainmenuconfig {
    menuitem_1 {
        id = 'menuitem-1'
        name='Home'
        sub=null
    }
    menuitem_2 {
        id ='menuitem-2'
        name='Stammdaten'
        sub = submenuitem_2 {
            menuitem_2_1 {
                id = 'menuitem-2-1'
                name ='Stamm-A'
                sub=null
            }
    }}
}

Retrieving the config via grailsApplication.config.get('mainmenuconfig') would give me the following:

[menuitem_1:[id:menuitem-1, name:Home, sub:null], menuitem_2:[id:menuitem-2, name:Stammdaten, submenuitem_2:[menuitem_2_1:[id:menuitem-2-1, name:Stamm-A]], sub:null]]

If I look at getClass() it says it's a org.grails.config.NavigableMap

Now, for my understanding, generating an <UL> ... <LI> tree should be done inside the View layer. For iterating through that structure, I will need recursion, because it can be n levels deep.

If I'm looking from main.gsp, I know the spot where I want to insert the menu tree, but how do I bring the data there and where do I do that recursion? Will I need a menu controller that is being called from the GSP? IMHO the GSP shouldn't do such calls. And on the other side, no controller should generate <UL> ... <LI> trees. I need the glue piece.

Answer 1

This sounds like a good use for an interceptor. You can have it add to your model after every action is finished. Then your view will have access to menu in its model and can build out the menu. It's fine to do recursion in your view if it's for display purposes.

class NavigationMenuInterceptor {

    NavigationMenuInterceptor() {
        matchAll()
    }

    boolean after() {
        model.menu = grailsApplication.config.getProperty('mainmenuconfig', Map)
        true
    }
}

To render your menu, you can use a template that recursively renders itself. Depending on your desired HTML output it might be something like below.

In the main body:

<ul>
    <g:each in="${menu}" var="menuitem">
        <g:render template="menuitem" model="[menuitem: menuitem]"/>
    </g:each>
</ul>

In your template _menuitem.gsp:

<li id="${menuitem.id}">
    ${menuitem.name}
</li>
<g:if test="${menuitem.sub}">
    <li>
        <ul>
            <g:render template="menuitem" model="[menuitem: menuitem.sub]"/>
        </ul>
    </li>
</g:if>