How to populate options of h:selectOneMenu from database?

user_844872 0
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I am creating a web application, where you have to read a list of objects / entities from a DB and populate it in a JSF <h:selectOneMenu>. I am unable to code this. Can someone show me how to do it?

I know how to get a List<User> from the DB. What I need to know is, how to populate this list in a <h:selectOneMenu>.

<h:selectOneMenu value="#{bean.name}">
    ...?
</h:selectOneMenu>
selectonemenu jsf database
5 Answers

I'm doing it like this:

  1. Models are ViewScoped

  2. converter:

    @Named
@ViewScoped
public class ViewScopedFacesConverter implements Converter, Serializable
{
        private static final long serialVersionUID = 1L;
        private Map<String, Object> converterMap;

        @PostConstruct
        void postConstruct(){
            converterMap = new HashMap<>();
        }

        @Override
        public String getAsString(FacesContext context, UIComponent component, Object object) {
            String selectItemValue = String.valueOf( object.hashCode() ); 
            converterMap.put( selectItemValue, object );
            return selectItemValue;
        }

        @Override
        public Object getAsObject(FacesContext context, UIComponent component, String selectItemValue){
            return converterMap.get(selectItemValue);
        }
}

and bind to component with:

 <f:converter binding="#{viewScopedFacesConverter}" />

If you will use entity id rather than hashCode you can hit a collision- if you have few lists on one page for different entities (classes) with the same id

Admin1

Call me lazy but coding a Converter seems like a lot of unnecessary work. I'm using Primefaces and, not having used a plain vanilla JSF2 listbox or dropdown menu before, I just assumed (being lazy) that the widget could handle complex objects, i.e. pass the selected object as is to its corresponding getter/setter like so many other widgets do. I was disappointed to find (after hours of head scratching) that this capability does not exist for this widget type without a Converter. In fact if you supply a setter for the complex object rather than for a String, it fails silently (simply doesn't call the setter, no Exception, no JS error), and I spent a ton of time going through BalusC's excellent troubleshooting tool to find the cause, to no avail since none of those suggestions applied. My conclusion: listbox/menu widget needs adapting that other JSF2 widgets do not. This seems misleading and prone to leading the uninformed developer like myself down a rabbit hole.

In the end I resisted coding a Converter and found through trial and error that if you set the widget value to a complex object, e.g.:

<p:selectOneListbox id="adminEvents" value="#{testBean.selectedEvent}">

... when the user selects an item, the widget can call a String setter for that object, e.g. setSelectedThing(String thingString) {...}, and the String passed is a JSON String representing the Thing object. I can parse it to determine which object was selected. This feels a little like a hack, but less of a hack than a Converter.

user_20856580
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