Module org.omnifaces
Package org.omnifaces.converter

Class SelectItemsConverter

java.lang.Object
org.omnifaces.converter.SelectItemsConverter
All Implemented Interfaces:
Converter<Object>
public class SelectItemsConverter extends Object implements Converter<Object>

The omnifaces.SelectItemsConverter allows you to populate a selection component with complex Java model objects (entities) as value of <f:selectItems> and have Faces convert those automatically back without the need to provide a custom converter which may need to do the job based on possibly expensive service/DAO operations. This converter automatically converts based on the Object.toString() of the selected item.

Usage

This converter is available by converter ID omnifaces.SelectItemsConverter. Just specify it in the converter attribute of the selection component holding <f:selectItems>. 

 <h:selectOneMenu value="#{bean.selectedItem}" converter="omnifaces.SelectItemsConverter">
     <f:selectItems value="#{bean.availableItems}" />
 </h:selectOneMenu>

Since OmniFaces 4.5 it's also available by <o:selectItemsConverter> tag. 

 <h:selectOneMenu value="#{bean.selectedItem}">
     <f:selectItems value="#{bean.availableItems}" />
     <o:selectItemsConverter />
 </h:selectOneMenu>

Make sure that your entity has a good toString() implementation

The base converter uses by default the toString() method of the entity to uniquely identify the instance during the conversion. This is sufficient if your (abstract base) entity has a toString() implementation which looks something like this: 

 @Override
 public String toString() {
     return String.format("%s[id=%d]", getClass().getSimpleName(), getId());
 }

By the way, you should also make sure that your entity has a good equals() and hashCode() implementation, otherwise Faces won't be able to set the right entity back in the model. Please note that this problem is in turn unrelated to the SelectItemsConverter, you would have faced the same problem when using any other converter.

If your entity can't have a good toString() implementation

However, if the entity doesn't have a toString() implementation (and thus relies on the default fqn@hashcode implementation), or the existing implementation doesn't necessarily uniquely identify the instance, and you can't implement/change it, then it is recommended to extend the SelectItemsConverter class and override only the getAsString method wherein the desired implementation is provided. For example: 

 @FacesConverter("exampleEntitySelectItemsConverter")
 public class ExampleEntitySelectItemsConverter extends SelectItemsConverter {

     @Override
     public String getAsString(FacesContext context, UIComponent component, Object value) {
         Long id = (value instanceof ExampleEntity) ? ((ExampleEntity) value).getId() : null;
         return (id != null) ? String.valueOf(id) : null;
     }

 }

Again, you do not need to override the getAsObject() method which would only need to perform possibly expensive service/DAO operations. The SelectItemsConverter base converter will already do it automatically based on the available items and the getAsString() implementation.

An alternative is to switch to SelectItemsIndexConverter, which will convert based on the position (index) of the selected item in the list instead of the Object.toString() of the selected item.

Author:
Arjan Tijms
See Also: