database value in backingBean

[Johan Rignas]

Hi. Is it possible to get database values into a backing bean?

I tried with this:

ModelBean:

@EJB
DatabaseImpl db;

public getVar(){
   db.getVar();
}

BackingBean:

@ManagedProperty(value = "#{modelBean}")
ModelBean modelBean;

private String var;

// Constructor
public BackBean(){
   var = modelBean.getVar();
}

The problem with this is that this gives me error(becouse I try to access modelBean in the cunstructor...):

Cant instantiate class: package.name.BackBean

I would like to get the data into BackingBean when it is created to be able to "update" the value later on. Any tips?

[Tim Holloway]

You cannot (usually) make an EJB/JPB Domain Model Object be a JSF backing bean because - while it's technically possible - they operate in different ways.

More often you'd use a backing bean as a container that fetches (and updates) the actual EJB, which you can present as a property of the backing bean.

Note that attempting to load objects from a database in a backing bean's constructor also isn't a good idea. For one thing, your database connection is best not hard-wired into the bean, and you can't inject the connection (or entityManager) at construction time. It's better to either do the object fetches in a @PostConstruct or in a separate pre-display method.

[Johan Rignas]

Ok. Thanks. But what about something like this:

ModelBean:

@EJB  
DatabaseImpl db;  

private String var;

public void init(){
   var = db.getVar();
}

public String getVar(){  
   return var;
}  

BackingBean:

@ManagedProperty(value = "#{modelBean}")  
ModelBean modelBean;

private String viewVar;

public String getVar(){
   viewVar = modelBean.getVar();
   return viewVar;
}

public void updateClicked(){
   ?????
}

If I just could get the value of a textfield with a given id it seems all will be solved. Any idea how to do this?
Something like this:

public void updateClicked(){
   FacesContext context = FacesContext.getCurrentInstance();
   UIViewRoot root = context.getViewRoot();
   Iterator<UIComponent> kids = root.getFacetsAndChildren();
   while (kids.hasNext()) {
            UIComponent found = findComponent(kids.next(), "textfieldID");
            if (found != null) {
                String txtValue = found.getValue(); // Psuedocode !!!!!!!!!!!!!!!!!!!!!!
            }
        }
}

[Johan Rignas]

Think I solved it with just a conversion inside my previous updateClicked():

HtmlInputText txt = (HtmlInputText)found;
String value = txt.getValue().toString();

[Johan Rignas]

Showed up this gives me the old value of the textField and not the new one.

Now I wounder: is there any hints on how I by a textfield can update a given row in a database with Beans?

WCS(worst case scenario) is that I have to go: jquery -> servlet -> database for an update and leave all beans out of it

[Tim Holloway]

In addition to not being able to use an Entity EJB as a backing bean, injecting an EJB into a backing bean doesn't usually work well for the same basic reason: you usually want the same EJB for every use of the backing bean, and injection requires you to specify a specific object at compile-time. You can, however, inject a DAO or Session EJB into the backing bean and use it to retrieve the instance that you want to work on. Once you do that, then the page can reference the bean and its properties using EL.

Please note that JSF is all about doing things for you. There's usually something wrong when your action processor method starts mucking around with the FacesContext, since the bean properties are automatically updated by JSF itself before the action method is invoked. And if one or more items fail validation, the bean won't be updated and the action method won't get invoked, so you can always be sure that only data that passes validation goes to the action processor.

Here's a minimalist sketch of a typical EJB/JSF interaction. It's not intended to be usable "as-is", but it does illustrate the major points. It's designed to display a form where you enter a keyvalue as text, then retrieve the EJB for that key, then redisplay the form with a few ejb properties:

@ManagedBean
@SessionScoped
public class MyBackingBean implements Serializable {

  /**
   * Session EJB constructed by Spring and injected via the Spring-JSF bridge
  */
   @ManagedProperty(value="#{mySessionEJB}")
   private MySessionEJB mySessionEJB;
   
   public void setMySessionEJB(MySessionEJB sessionEJB) {
      this.mySessionEJB = sessionEJB;
  }

  /**
   * The EJB. Initialized to an empty EJB to avoid annoying the initial
   * page display's EL property references
   */
  private MyEJB myEJB = new MyEJB();

  // Add get/set MyEJB methods here.


  /**
   * EJB key entered by user
  */
   private String myKey = "";

  // Add get/set MyKey methods here
   /**
   * User has entered a key value on the form. Fetch the EJB
   */
   public void doFindEJB() {
       MyEJB ejb = mySessionEJB.findByPrimaryKey(ejbKey);
       if ( ejb == null ) {
            // JSFUtils is a utility class I have that simplifies certain JSF
            // functions and keeps explicit JSF logic out of general-purpose beans.
            JSFUtils.addErrorMessage("Item not found");
            return;
      }
      this.myEJB = ejb;
   }

  /**
   * Once the bean has been updated by the user, save it
   * and proceed to the next View.
   */
   public String doUpdateEJB() {
     mySessionEJB.updateEJB(this.myEJB);
     return "nextPage";
   }   
}

Now for the View definition:

<h:form id="myform">
   <h:messages/>
   <h:panelGrid id="grid1" columns="3">
     <h:outputLabel for="ejbKey" value="Item key: "/>
     <h:inputText id="ejbKey" value="#{myBackingBean.myKey}" required="true" maxlength="10"/>
     <h:commandButton action="#{myBackingBean.doFindEJB}"/>
   <h:panelGrid>

   <h:panelGrid id="ejbGrid" columns="2">
     <h:outputLabel for="ejbId" value="Key: "/>
     <h:outputText id="ejbId" value="#{myBackingBean.myEJB.id}"/>

     <h:outputLabel for="ejbDesc" value="Description: "/>
     <h:outputText id="ejbDesc" value="#{myBackingBean.myEJB.description}"/>

     <h:outputText i value=""/>
     <h:commandButton action="#{myBackingBean.doUpdateEJB}"/>

   <h:panelGrid>
</h:form>

[Johan Rignas]

Thanks!! Tried to do the same thing as you and it worked!

But I would like the values to show directly. Becouse of this I made one extra view page. This is how it looks:

index.jsf(just to fill the textField):

<h:commandLink value="goToForm" action="#{backingBean.fillFields}" />

backingBean(Session scope):

@ManagedProperty(value = "#{modelBean}")
ModelBean modelBean;

@EJB
DatabaseImpl db;

private String myVar;
/** Getters and setters for myVar */

public String fillFields() {
       myVar = modelBean.getVar();
       return "viewPage";
}

public void update() {
    modelBean.setVar(myVar);
    db.updateMyVar(myVar);
}

viewPage:

<h:inputText value="#{backingBean.myVar}" />
<h:commandButton value="Update!" action="#{backingBean.update}" />

Any comments on how this can be improved are welcome.

[Tim Holloway]

That's what I do as well. For CRUD operations, I usually have 2 methods used to prep a backing bean for edit and display and name them "beginAdd" and "beginEdit". One sets up a blank EJB to be added, the other fetches an existing EJB.

Because "beginEdit" normally takes a primary key (after all, you have to know which EJB to edit!), I usually inject the backing bean into a setup bean which implements the initial choice to create or edit and allows input of the key value. Then the setup bean's action processor invokes the beginEdit(key) method in the injected editor backing bean.