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<h1><a name="top"></a>NetBeans Platform CRUD Application Tutorial</h1>

  <p>This tutorial shows you how to integrate a Java DB database into a
   NetBeans Platform application. We start by exploring a Java DB database,
   from which we create entity classes. However, note that these instructions
   are not applicable to Java DB only. Rather, they are relevant to any
   relational database supported by NetBeans IDE. Next, we wrap the entity classes
   into a module, together with modules for the related JPA JARS.

  <p>Once the above modules are part of our application, we create a new
   module that provides the user interface for our application. The
   new module gives the user a tree hierarchy showing data from the database.
   We then create another module that lets the user edit the data displayed
   by the first module. By separating the viewer from the editor in distinct modules, we will enable
   the user to install a different editor for the same viewer, since different
   editors could be created by external vendors, some commercially and some
   for free. It is this flexibility that the modular architecture of the
   NetBeans Platform makes possible.

  <p>Once we have an editor, we begin adding CRUD functionality. First, the
  "R", standing for "Read", is handled by the viewer described above. Next,
  the "U" for "Update" is handled, followed by the "C" for "Create", and the
  "D" for "Delete".

  <p>At the end of the tutorial, you will have learned about a range of NetBeans
  Platform features that help you in creating applications of this kind. For
  example, you will have learned about the <tt><a href="http://bits.netbeans.org/dev/javadoc/org-openide-awt/org/openide/awt/UndoRedo.Manager.html">UndoRedo.Manager</a></tt> and the <tt><a href="http://bits.netbeans.org/dev/javadoc/org-openide-explorer/org/openide/explorer/ExplorerManager.html">ExplorerManager</a></tt>,
  as well as NetBeans Platform Swing components, such as <tt><a href="http://bits.netbeans.org/dev/javadoc/org-openide-windows/org/openide/windows/TopComponent.html">TopComponent</a></tt> and <tt><a href="http://bits.netbeans.org/dev/javadoc/org-openide-explorer/org/openide/explorer/view/BeanTreeView.html">BeanTreeView</a></tt>.

   <p><b class="notes">Note:</b> This document uses the NetBeans IDE 6.8 Release. If you
    are using an earlier version, see <a href="67/nbm-crud.html">the 6.7 version
    of this document</a>.</p>

   <p><b>Contents</b></p>
         
       <img  src="../images/articles/68/netbeans-stamp.gif" class="stamp" width="114" height="114" alt="Content on this page applies to NetBeans IDE 6.8" title="Content on this page applies to NetBeans IDE 6.8">
      <ul class="toc">
        <li><a href="#creating-app">Setting Up the Application</a></li>
        <li><a href="#integrating-database">Integrating the Database</a>
        <ul>
            <li><a href="#creating-entity">Creating Entity Classes from a Database</a></li>
            <li><a href="#wrapping-entity">Wrapping the Entity Class JAR in a Module</a></li>
            <li><a href="#creating-other">Creating Other Related Modules</a></li>
            <li><a href="#designing-ui">Designing the User Interface</a></li>
            <li><a href="#setting-dependencies">Setting Dependencies</a></li>
            <li><a href="#running-prototype">Running the Prototype</a></li>
        </ul>
        <li><a href="#integrating-crud">Integrating CRUD Functionality</a>
        <ul>
            <li><a href="#read">Read</a></li>
            <li><a href="#update">Update</a></li>
            <li><a href="#create">Create</a></li>
            <li><a href="#delete">Delete</a></li>
        </ul>
        </li>
      </ul>
         
<p><b>To follow this tutorial, you need the software and resources listed in the following 
table.</b></p>

 <table>
        <tbody>
            <tr>
                <th class="tblheader" scope="col">Software or Resource</th>
                <th class="tblheader" scope="col">Version Required</th>
            </tr> 
            <tr>
                <td class="tbltd1"><a href="https://netbeans.org/downloads/index.html">NetBeans IDE</a></td>
                <td class="tbltd1">version 6.8</td>
            </tr>
            <tr>
                <td class="tbltd1"><a href="http://java.sun.com/javase/downloads/index.jsp">Java Developer Kit (JDK)</a></td>
                <td class="tbltd1">Version 6 or<br/>version 5</td>
            </tr>
        </tbody>
    </table>
    
    <p>The application you create in this tutorial will
    look as follows:</p>

<p><img alt="the final state of the application" src="http://netbeans.dzone.com/sites/all/files/customer-app-on-nb.png"/> </p>

<p class="tips"> It is advisable to watch the screencast series
 <a href="https://platform.netbeans.org/tutorials/nbm-10-top-apis.html">Top 10 NetBeans APIs</a>
 before beginning to work on this tutorial. Many of the concepts addressed in this tutorial
 are discussed in more detail within the screencast series.


    <p>
<!-- ===================================================================================== -->  

<br>
<h2 class="tutorial"><a name="creating-app"></a>Setting up the Application</h2>

<p>Let's start by creating a new NetBeans Platform application.

<ol>
    <li>Choose File &gt; New Project (Ctrl+Shift+N). Under Categories, select NetBeans Modules. 
        Under Projects, select NetBeans Platform Application. Click Next.</li>
    <li>In the Name and Location panel, type <tt>DBManager</tt> in the Project Name field.
         Click Finish.</li>
</ol>
    
<p>The IDE creates the <tt>DBManager</tt> project. The project
 is a container for all the other modules you will create.

<p><img alt="NetBeans Platform container" src="../images/tutorials/crud/68dbmanager-1.png"/> </p>

<br>

<!-- ===================================================================================== -->

<br>
<h2><a name="integrating-database"></a>Integrating the Database</h2>

<p>In order to integrate the database, you need to create entity classes
 from your database and integrate those entity classes, together with
 their related JARs, into modules that are part of your NetBeans Platform
 application.</p>

<div class="indent">
    <h3 class="tutorial"><a name="creating-entity"></a>Creating the Entity Classes</h3>
    <p>In this section, you generate entity classes from a selected database.
    <ol>
        <li>For purposes of this example, use the Services window to
                connect to the sample database that is included with
                NetBeans IDE:

        <p><img alt="Services window" src="../images/tutorials/crud/68dbmanager-2.png"/> </p>

        <p class="tips"> Alternatively, use
        any database you like and adapt the steps that follow to your particular
        use case. In the case of MySQL, see <a href="https://netbeans.org/kb/docs/ide/mysql.html">Connecting to a MySQL Database</a>.</p>
        <p><li>In the IDE, choose File | New Project, followed by
         Java | Java Class Library to create a new library project
         named <tt>CustomerLibrary</tt>.
        <p><li>In the Projects window, right-click the library project
         and choose File | New File, followed by Persistence | Entity
         Classes from Database. In the wizard, select your database and the tables you
         need. Here we choose "Customer", and then "Discount Code" is added automatically, since
         there is a relationship between these two tables.

                 <p><img alt="adding tables" src="../images/tutorials/crud/68dbmanager-3.png"/> </p>


                 <p><li>Specify the persistence strategy, which can
                     be any of the available options. Here, since we need
                     to choose something, we'll
                     choose EclipseLink:

                             <p><img alt="choosing eclipselink" src="../images/tutorials/crud/68dbmanager-4.png"/> </p>


                            <p><li>Specify "demo" as the name of
        the package where the entity classes will be generated.
                             <p><img alt="name of package" src="../images/tutorials/crud/68dbmanager-5.png"/> </p>

        <p><li>Click Finish. Once you have completed this step, look at the generated code and notice
         that, among other things, you now have a <tt>persistence.xml</tt> file in a folder
        called META-INF, as well as entity classes for each of your tables:

<p><img alt="entity classes" src="../images/tutorials/crud/68dbmanager-7.png"/> </p>

         <p><li>Build the Java Library and you will have a JAR file in the library
         project's "dist" folder, which you can view in the Files window:

<p><img alt="dist folder" src="../images/tutorials/crud/68dbmanager-8.png"/> </p>

         </li>
    </ol>
    
    <h3 class="tutorial"><a name="wrapping-entity"></a>Wrapping the Entity Class JAR in a Module</h3>
    <p>In this section, you add your first module to your application!
        The new NetBeans module will wrap the JAR file
     you created in the previous section. 
    <ol>
        <li>Right-click the <tt>DBManager</tt>'s Modules node in the Projects window
         and choose Add New Library.
        <p><li>Select the JAR you created in the previous subsection
         and complete the wizard, specifying any values you like. Let's assume
         the application is for dealing with customers at shop.org, in which case
         a unique identifier "org.shop.model" is appropriate for the code name base:

         <p><img alt="unique id for module" src="../images/tutorials/crud/68dbmanager-9.png"/> </p>

    </ol>
        <p>You now have your first custom module in your new application,
             wrapping the JAR containing the entity classes and
             the persistence.xml file:</p>

        <p><img alt="persistence.xml" src="../images/tutorials/crud/68dbmanager-91.png"/> </p>

    <h3 class="tutorial"><a name="creating-other"></a>Creating Other Related Modules</h3>
    <p>In this section, you create two new modules, wrapping the EclipseLink JARs,
     as well as the database connector JAR.
    <ol>
        <li>Do the same as you did when creating the library wrapper for the
        entity class JAR, but this time for the EclipseLink JARs, which are in
        the "CustomerLibrary" Java library that you created earlier:

                <p><img alt="wrapping a library" src="../images/tutorials/crud/68dbmanager-94.png"/></p>


        <p class="tips"> In the Library Wrapper Module wizard,
             you can use Ctrl-Click to select multiple JARs.</p>

        <p><li>Next, create yet another library wrapper module, this time for the Java DB client JAR,
        which is available in your JDK distribution, at <tt>db/lib/derbyclient.jar</tt>.
    </ol>
    
    <h3 class="tutorial"><a name="designing-ui"></a>Designing the User Interface</h3>
    <p>In this section, you create a simple prototype user interface, providing
        a window that uses a <tt>JTextArea</tt> to display data retrieved
        from the database.
    <ol>
        <li>Right-click the <tt>DBManager</tt>'s Modules node in the Projects window
         and choose Add New. Create a new module named <tt>CustomerViewer</tt>, with
         the code name base <tt>org.shop.ui</tt>.
        <p><li>In the Projects window, right-click the new module and choose
         New | Window Component. Specify that it should be created in the <tt>editor</tt>
         position and that it should open when the application starts. Set <tt>Customer</tt>
         as the window's class name prefix.
        <p><li>Use the Palette (Ctrl-Shift-8) to drag
        and drop a <tt>JTextArea</tt> on the new window:

        <p><img alt="JTextArea dropped" src="../images/tutorials/crud/68dbmanager-93.png"/></p>

       <p><li>Add this
       to the end of the TopComponent constructor:
<pre class="examplecode">EntityManager entityManager = Persistence.createEntityManagerFactory("CustomerLibraryPU").createEntityManager();
Query query = entityManager.createQuery("SELECT c FROM Customer c");
List&lt;Customer&gt; resultList = query.getResultList();
for (Customer c : resultList) {
  jTextArea1.append(c.getName() + " (" + c.getCity() + ")" + "\n");
}</pre>

<p class="tips"> Since you have not set dependencies on the modules that
 provide the Customer object and the persistence JARs, the statements
 above will be marked with red error underlines. These will be fixed
in the section that follows.</p>

<p>Above, you can see references to a persistence unit named "CustomerLibraryPU",
which is the name set in the <tt>persistence.xml</tt> file. In addition,there is a reference
to one of the entity classes, called <tt>Customer</tt>, which is in the entity classes module.
Adapt these bits to your needs, if they are different to the above.

    </ol>

    <h3 class="tutorial"><a name="setting-dependencies"></a>Setting Dependencies</h3>
    <p>In this section, you enable some of the modules to use code from
     some of the other modules. You do this very explicitly by setting intentional
     contracts between related modules, i.e., as opposed
     to the accidental and chaotic reuse of code that tends to happen when
     you do not have a strict modular architecture such as that provided by
     the NetBeans Platform.
    <ol>
         <li>The entity classes module needs to have dependencies on the Derby Client
        module as well as on the EclipseLink module. Right-click the
        <tt>CustomerLibrary</tt> module, choose Properties, and use the
        Libraries tab to set dependencies on the two modules that the
        <tt>CustomerLibrary</tt> module needs.
        <p><li>The <tt>CustomerViewer</tt> module needs a dependency
        on the EclipseLink module as well as on the entity classes module.
        Right-click the
        <tt>CustomerViewer</tt> module, choose Properties, and use the
        Libraries tab to set dependencies on the two modules that the
        <tt>CustomerViewer</tt>  module needs.
        <p><li>Open the <tt>CustomerTopComponent</tt> in the Source view, right-click
        in the editor, and choose "Fix Imports". The IDE is now able to add
        the required import statements, because the modules that provide
        the required classes are now available to the <tt>CustomerTopComponent</tt>.
    </ol>
        <p>You now have set contracts between the modules
         in your application, giving you control
         over the dependencies between distinct pieces
         of code.

    <h3 class="tutorial"><a name="running-prototype"></a>Running the Prototype</h3>
    <p>In this section, you run the application so that you can see
     that you're correctly accessing your database.
    <ol>
        <li>Start your database server.
        <p><li>Run the application. You should see this:

        <p><img alt="running the prototype" src="../images/tutorials/crud/68dbmanager-92.png"/></p>
    </ol>
        <p>You now have a simple prototype, consisting of a NetBeans Platform
            application that displays data from your database,
            which you will extend in the next
         section.

</div>

<br>
<h2><a name="integrating-crud"></a>Integrating CRUD Functionality</h2>

<p>In order to create CRUD functionality that integrates smoothly
 with the NetBeans Platform, some very specific NetBeans Platform coding patterns need to
 be implemented. The sections that follow describe these patterns
 in detail.</p>

<div class="indent">
    
    <h3 class="tutorial"><a name="read"></a>Read</h3>
    <p>In this section, you change the <tt>JTextArea</tt>, introduced in the
     previous section, for a NetBeans Platform explorer view. NetBeans Platform
     explorer views are Swing components that integrate better with the
     NetBeans Platform than standard Swing components do. Among other things,
     they support the notion of a context, which enables them to be
     context sensitive.
    <p>Representing your data,
     you will have a generic hierarchical model provided by a NetBeans Platform
     <tt>Node</tt> class, which can be displayed by any of the NetBeans Platform
     explorer views. This section ends with an explanation of how to synchronize
     your explorer view with the NetBeans Platform Properties window.
    <ol>
        <li>In your <tt>TopComponent</tt>, delete the <tt>JTextArea</tt>
         in the Design view and comment out its
         related code in the Source view:

<pre class="examplecode">EntityManager entityManager =  Persistence.createEntityManagerFactory("CustomerLibraryPU").createEntityManager();
Query query = entityManager.createQuery("SELECT c FROM Customer c");
List&lt;Customer&gt; resultList = query.getResultList();
//for (Customer c : resultList) {
//    jTextArea1.append(c.getName() + " (" + c.getCity() + ")" + "\n");
//}</pre>

<p><li>Right-click the <tt>CustomerViewer</tt> module, choose Properties,
 and use the Libraries tab to set dependencies on the Nodes API and
 the Explorer & Property Sheet API.

<p><li>Next, change the class signature to implement <tt>ExplorerManager.Provider</tt>:

<pre class="examplecode">final class CustomerTopComponent extends TopComponent implements ExplorerManager.Provider</pre>

<p>You will need to override <tt>getExplorerManager()</tt>

<pre class="examplecode">@Override
public ExplorerManager getExplorerManager() {
    return em;
}</pre>

<p>At the top of the class, declare and initialize the <tt>ExplorerManager</tt>:

<pre class="examplecode">private static ExplorerManager em = new ExplorerManager();</pre>

<p class="tips"> Watch <a href="https://platform.netbeans.org/tutorials/nbm-10-top-apis.html">Top 10 NetBeans APIs</a>
 for details on the above code, especially the screencast dealing with the Nodes API
 and the Explorer & Property Sheet API.

<p><li>Switch to the <tt>TopComponent</tt> Design view,
 right-click in the Palette, choose Palette Manager | Add from JAR. Then browse to
 the <tt>org-openide-explorer.jar</tt>, which is in <tt>platform11/modules</tt> folder,
 within the NetBeans IDE installation directory. Choose the BeanTreeView and complete
 the wizard. You should now see <tt>BeanTreeView</tt> in the Palette. Drag it from
 the Palette and drop it on the window.
 
<p><li>Create a factory class that will create a new <a href="http://bits.netbeans.org/dev/javadoc/org-netbeans-modules-db/org/netbeans/api/db/explorer/node/BaseNode.html">BeanNode</a>
             for each customer in your database:

<pre class="examplecode">import demo.Customer;
import java.beans.IntrospectionException;
import java.util.List;
import org.openide.nodes.BeanNode;
import org.openide.nodes.ChildFactory;
import org.openide.nodes.Node;
import org.openide.util.Exceptions;

public class CustomerChildFactory extends ChildFactory&lt;Customer&gt; {

    private List&lt;Customer&gt; resultList;

    public CustomerChildFactory(List&lt;Customer&gt; resultList) {
        this.resultList = resultList;
    }

    @Override
    protected boolean createKeys(List&lt;Customer&gt; list) {
        for (Customer Customer : resultList) {
            list.add(Customer);
        }
        return true;
    }

    @Override
    protected Node createNodeForKey(Customer c) {
        try {
            return new BeanNode(c);
        } catch (IntrospectionException ex) {
            Exceptions.printStackTrace(ex);
            return null;
        }
    }

}</pre>
        <p><li>Back in the <tt>CustomerTopComponent</tt>,
         use the <tt>ExplorerManager</tt> to pass the result list
        from the JPA query in to the <tt>Node</tt>:

<pre class="examplecode">EntityManager entityManager =  Persistence.createEntityManagerFactory("CustomerLibraryPU").createEntityManager();
Query query = entityManager.createQuery("SELECT c FROM Customer c");
List&lt;Customer&gt; resultList = query.getResultList();
<b>em.setRootContext(new AbstractNode(Children.create(new CustomerChildFactory(resultList), true)));</b>
//for (Customer c : resultList) {
//    jTextArea1.append(c.getName() + " (" + c.getCity() + ")" + "\n");
//}</pre>

        <p><li>Run the application. Once the application is running,
         open the Properties window. Notice that even though the data
         is available, displayed in a <tt>BeanTreeView</tt>, the <tt>BeanTreeView</tt>
         is not synchronized with the Properties window, which is available
         via Window | Properties. In other words, nothing is displayed
        in the Properties window when you move up and down the tree hierarchy.

        <p><li>Synchronize the Properties window with the <tt>BeanTreeView</tt>
        by adding the following to the constructor in the <tt>TopComponent</tt>:

<pre class="examplecode">associateLookup(ExplorerUtils.createLookup(em, getActionMap()));</pre>

<p>Here we add the <tt>TopComponent</tt>'s <tt>ActionMap</tt> and <tt>ExplorerManager</tt>
 to the <tt>Lookup</tt> of the <tt>TopComponent</tt>. A side effect of this is
 that the Properties window starts displaying the display name and tooltip text
 of the selected <tt>Node</tt>.

        <p><li>Run the application again and notice that the Properties window
        is now synchronized with the explorer view:

        <p><img alt="synchronization" src="../images/tutorials/crud/68dbmanager-95.png"/>

    </ol>
    <p>Now you are able to view your data in a tree hierarchy, as you would
     be able to do with a <tt>JTree</tt>. However, you're also able to swap
     in a different explorer view without needing to change the model at all
     because the <tt>ExplorerManager</tt> mediates between the model and the
     view. Finally, you are now also able to synchronize the view with the
     Properties window.

    <h3 class="tutorial"><a name="update"></a>Update</h3>
    <p>In this section, you first create an editor. The editor will be provided
     by a new NetBeans module. So, you will first create a new module. Then, within
     that new module, you will create a new <tt>TopComponent</tt>, containing two <tt>JTextFields</tt>,
     for each of the columns you want to let the user edit. You will need to
     let the viewer module communicate with the editor module. Whenever a new
     <tt>Node</tt> is selected in the viewer module, you will add the current <tt>Customer</tt>
     object to the <tt>Lookup</tt>. In the editor module, you will listen to the
     <tt>Lookup</tt> for the introduction of <tt>Customer</tt> objects. Whenever a
     new <tt>Customer</tt> object is introduced into the <tt>Lookup</tt>, you will
     update the <tt>JTextFields</tt> in the editor.
    <p>Next, you will synchronize your <tt>JTextFields</tt>
     with the NetBeans Platform's Undo, Redo, and Save functionality. In other words,
     when the user makes changes to a <tt>JTextField</tt>, you want the
     NetBeans Platform's existing functionality to become available so that,
     instead of needing to create new functionality, you'll simply be able to
     hook into the NetBeans Platform's support. To
     this end, you will need to use the <tt>UndoRedoManager</tt>, together with the
     <tt>SaveCookie</tt>.
    <ol>
        <li>Create a new module, named <tt>CustomerEditor</tt>, with <tt>org.shop.editor</tt> as
         its code name base.
        <p><li>Right-click the <tt>CustomerEditor</tt> module and choose New | Window Component.
         Make sure to specify that the window should appear in the <tt>editor</tt> position and
         that it should open when the application starts. In the final panel of the wizard,
         set "Editor" as the class name prefix.
        <p><li>Use the Palette (Ctrl-Shift-8) to add two <tt>JLabels</tt> and two <tt>JTextFields</tt>
         to the new window. Set the texts of the labels to "Name" and "City" and
         set the variable names of the two <tt>JTextFields</tt> to <tt>jTextField1</tt>
        and <tt>jTextField2</tt>.

        <p>In the GUI Builder, the window should now look something like this:</p>

        <p><img alt="designing the user interface" src="../images/tutorials/crud/68dbmanager-96.png"/></p>

        <p><li>Go back to the <tt>CustomerViewer</tt> module and change its <tt>layer.xml</tt>
         file to specify that the <tt>CustomerTopComponent</tt> window will appear in the <tt>explorer</tt> mode.

         <p class="tips"> Right-click the application project and choose "Clean", after
          changing the <tt>layer.xml</tt> file. Why? Because whenever you run the
          application and close it down, the window positions are stored in the
          user directory. Therefore, if the <tt>CustomerViewer</tt> was initially
          displayed in the <tt>editor</tt> mode, it will remain in the <tt>editor</tt> mode,
          until you do a "Clean", thus resetting the user directory (i.e., thus
          <i>deleting</i> the user directory) and enabling
          the <tt>CustomerViewer</tt> to be displayed in the position currently set in the
         <tt>layer.xml</tt> file.</p>


         <p>Also check
         that the <tt>BeanTreeView</tt> in the <tt>CustomerViewer</tt> will stretch horizontally
         and vertically when the user resizes the application. Check this by opening the window,
         selecting the <tt>BeanTreeView</tt>, and then clicking the arrow buttons in the
         toolbar of the GUI Builder.

         <li>Run the application and make sure that you see the following when the
              application starts up:

                      <p><img alt="running the new UI" src="../images/tutorials/crud/68dbmanager-97.png"/></p>


        <li>Now we can start adding some code.
         Firstly, we need to show the currently selected Customer object in the editor:
        <ul>
         <li>Start by tweaking the <tt>CustomerViewer</tt> module so that the current <tt>Customer</tt> object
         is added to the viewer window's <tt>Lookup</tt> whenever a new <tt>Node</tt>
         is selected. Do this by creating an <tt>AbstractNode</tt>, instead of a <tt>BeanNode</tt>,
         in the <tt>CustomerChildFactory</tt> class. That enables you to add the
         current <tt>Customer</tt> object to the <tt>Lookup</tt> of the Node,
          as follows (note the part in bold):

<pre class="examplecode">@Override
protected Node createNodeForKey(Customer c) {
    Node node = new AbstractNode(Children.LEAF, Lookups.singleton(c));
    node.setDisplayName(c.getName());
    node.setShortDescription(c.getCity());
    return node;
//        try {
//            return new BeanNode(c);
//        } catch (IntrospectionException ex) {
//            Exceptions.printStackTrace(ex);
//            return null;
//        }
}</pre>

        <p>Now, whenever a new <tt>Node</tt> is created, which
         happens when the user selects a new customer in the viewer, a new
         <tt>Customer</tt> object is added to the <tt>Lookup</tt> of the <tt>Node</tt>.

         <p><li>Let's
         now change the editor module in such a way that its window
         will end up listening for <tt>Customer</tt> objects being added to the <tt>Lookup</tt>. First,
         set a dependency in the editor module on the module that provides
         the entity class, as well as the module that provides the persistence
         JARs. 

         <p><li>Next, change the <tt>EditorTopComponent</tt> class signature
         to implement <tt>LookupListener</tt>:

<pre class="examplecode">public final class EditorTopComponent extends TopComponent implements LookupListener</pre>

         <p><li>Override the
         <tt>resultChanged</tt> so that the <tt>JTextFields</tt> are updated whenever
         a new <tt>Customer</tt> object is introduced into the <tt>Lookup</tt>:

<pre class="examplecode">@Override
public void resultChanged(LookupEvent lookupEvent) {
    Lookup.Result r = (Lookup.Result) lookupEvent.getSource();
    Collection&lt;Customer&gt; coll = r.allInstances();
    if (!coll.isEmpty()) {
        for (Customer cust : coll) {
            jTextField1.setText(cust.getName());
            jTextField2.setText(cust.getCity());
        }
    } else {
        jTextField1.setText("[no name]");
        jTextField2.setText("[no city]");
    }
}</pre>

        <p><li>Now that the <tt>LookupListener</tt> is defined,
         we need to add it to something. Here, we add it to
         the <tt>Lookup.Result</tt> obtained from the global context.
         The global context proxies the context of the selected <tt>Node</tt>.
         For example, if "Ford Motor Co" is selected in the tree hierarchy,
         the <tt>Customer</tt> object for "Ford Motor Co" is added to the <tt>Lookup</tt>
         of the <tt>Node</tt> which, because it is the currently selected <tt>Node</tt>,
         means that the <tt>Customer</tt> object for "Ford Motor Co" is now available in
         the global context. That is what is then passed to the <tt>resultChanged</tt>,
        causing the text fields to be populated.

         <p>All of the above starts happening, i.e., the <tt>LookupListener</tt>
         becomes active, whenever the editor window is opened, as you can see below:</p>

<pre class="examplecode">@Override
public void componentOpened() {
    result = Utilities.actionsGlobalContext().lookupResult(Customer.class);
    result.addLookupListener(this);
    resultChanged(new LookupEvent(result));
}

@Override
public void componentClosed() {
    result.removeLookupListener(this);
    result = null;
}</pre>

<p>Since the editor window is opened when the application starts, the
 <tt>LookupListener</tt> is available at the time that the application starts up.

<p><li>Finally, declare the result variable at the top of the class, like this:

<pre class="examplecode">private Lookup.Result result = null;</pre>

        <p><li>Run the application again and notice that the editor window
        is updated whenever you select a new <tt>Node</tt>:

                      <p><img alt="updated editor window" src="../images/tutorials/crud/68dbmanager-98.png"/></p>


<p>However, notice what happens when you switch the focus to the editor window:</p>

                      <p><img alt="switch focus" src="../images/tutorials/crud/68dbmanager-99.png"/></p>

<p>Because the <tt>Node</tt> is no longer current, the <tt>Customer</tt> object
 is no longer in the global context. This is the case because, as pointed out
 above, the global context proxies the <tt>Lookup</tt> of the current <tt>Node</tt>.
 Therefore, in this case, we cannot use the global context. Instead, we will
use the local <tt>Lookup</tt> provided by the Customer window.</p>

<p>Rewrite this line:

<pre class="examplecode">result = Utilities.actionsGlobalContext().lookupResult(Customer.class);</pre>

<p>To this:

<pre class="examplecode">result = WindowManager.getDefault().findTopComponent("CustomerTopComponent").getLookup().lookupResult(Customer.class);</pre>

<p>The string "CustomerTopComponent" is the ID of the <tt>CustomerTopComponent</tt>, which
 is a string constant that you can find in the source code of the <tt>CustomerTopComponent</tt>. One
 drawback of the approach above is that now our <tt>EditorTopComponent</tt> only works if it
 can find a <tt>TopComponent</tt> with the ID "CustomerTopComponent". Either this needs to
 be explicitly documented, so that developers of alternative editors can know that they
 need to identify the viewer <tt>TopComponent</tt> this way, or you need to rewrite the
 selection model, <a href="http://weblogs.java.net/blog/timboudreau/archive/2007/01/how_to_replace.html">as described here</a> by Tim Boudreau.

<p>If you take one of the above approaches, you will find that the context is not lost
when you switch the focus to the <tt>EditorTopComponent</tt>, as shown below:</p>

                      <p><img alt="context is not lost" src="../images/tutorials/crud/68dbmanager-991.png"/></p>

<p class="tips"> Since you are now using <tt>AbstractNode</tt>, instead of <tt>BeanNode</tt>,
     no properties are shown in the Properties window. You need to provide these yourself,
     as described in the <a href="https://platform.netbeans.org/tutorials/nbm-nodesapi2.html">Nodes API Tutorial</a>.
        </ul>
        <li>Secondly, let's work on the Undo/Redo functionality. What we'd
         like to have happen is that whenever the user makes a change to one
         of the <tt>JTextFields</tt>, the "Undo" button and the "Redo" button,
         as well as the related menu items in the Edit menu, become enabled. To
         that end, the NetBeans Platform makes the <a href="http://bits.netbeans.org/dev/javadoc/org-openide-awt/org/openide/awt/UndoRedo.Manager.html">UndoRedo.Manager</a> available.
        <ul>
        <li>Declare and instantiate a new UndoRedoManager at the top of the
         <tt>EditorTopComponent</tt>:

<pre class="examplecode">private UndoRedo.Manager manager = new UndoRedo.Manager();</pre>

        <p><li>Next, override the <tt>getUndoRedo()</tt> method in the <tt>EditorTopComponent</tt>:

<pre class="examplecode">@Override
public UndoRedo getUndoRedo() {
    return manager;
}</pre>

        <p><li>In the constructor of the <tt>EditorTopComponent</tt>, add
         a <tt>KeyListener</tt> to the <tt>JTextFields</tt> and, within
         the related methods that you need to implement, add the <tt>UndoRedoListeners</tt>:

<pre class="examplecode">jTextField1.getDocument().addUndoableEditListener(manager);
jTextField2.getDocument().addUndoableEditListener(manager);
</pre>

        <p><li>Run the application and show the Undo and Redo functionality in action,
        the buttons as well as the menu items. The functionality works exactly as you would expect. You might want to
 change the <tt>KeyListener</tt> so that not ALL keys cause the undo/redo
 functionality to be enabled. For example, when Enter is pressed, you probably
 do not want the undo/redo functionality to become available. Therefore, tweak
the code above to suit your business requirements.


        </ul>
        <li>Thirdly, we need to
         integrate with the NetBeans Platform's Save functionality:
        <ul>
        <li>By default, the "Save All" button is available in the
         NetBeans Platform toolbar. In our current scenario, we do not
         want to save "all", because "all" refers to a number of different
         documents. In our case, we only have one "document", which is the
         editor that we are reusing for all the nodes in the tree hirerarchy.
         Remove the "Save All" button and add the "Save" button instead, by adding
         the following to the layer file of the <tt>CustomerEditor</tt> module:

<pre class="examplecode">&lt;folder name="Toolbars"&gt;
    &lt;folder name="File"&gt;
        &lt;file name="org-openide-actions-SaveAction.shadow"&gt;
            &lt;attr name="originalFile" stringvalue="Actions/System/org-openide-actions-SaveAction.instance"/&gt;
            &lt;attr name="position" intvalue="444"/&gt;
        &lt;/file&gt;
        &lt;file name="org-openide-actions-SaveAllAction.shadow_hidden"/&gt;
    &lt;/folder&gt;
&lt;/folder&gt;</pre>

<p>When you now run the application, you will see a different icon
 in the toolbar. Instead of the "Save All" button, you now have
 the "Save" button available.

        <p><li>Set dependencies on the Dialogs API and the Nodes API.

            <p><li>In the <tt>EditorTopCompontn</tt> constructor, add a
             call to fire a method (which will be defined in the next step)
             whenever a change is detected:

<pre class="examplecode">public EditorTopComponent() {

        ...
        ...
        ...

        jTextField1.getDocument().addDocumentListener(new DocumentListener() {
            public void insertUpdate(DocumentEvent arg0) {
                fire(true);
            }
            public void removeUpdate(DocumentEvent arg0) {
                fire(true);
            }
            public void changedUpdate(DocumentEvent arg0) {
                fire(true);
            }
        });

        jTextField2.getDocument().addDocumentListener(new DocumentListener() {
            public void insertUpdate(DocumentEvent arg0) {
                fire(true);
            }
            public void removeUpdate(DocumentEvent arg0) {
                fire(true);
            }
            public void changedUpdate(DocumentEvent arg0) {
                fire(true);
            }
        });

        //Create a new instance of our SaveCookie implementation:
        impl = new SaveCookieImpl();

        //Create a new instance of our dynamic object:
        content = new InstanceContent();

        //Add the dynamic object to the TopComponent Lookup:
        associateLookup(new AbstractLookup(content));

    }

    ...
    ...
    ...
</pre>

             <p><li>Here are the two methods referred to above. First, the method
             that is fired whenever a change is detected. An implementation of
             the <tt>SaveCookie</tt> from the Nodes API is added to the <tt>InstanceContent</tt>
             whenever a change is detected:

<pre class="examplecode">    public void fire(boolean modified) {
        if (modified) {
            //If the text is modified,
            //we add SaveCookie impl to Lookup:
            content.add(impl);
        } else {
            //Otherwise, we remove the SaveCookie impl from the lookup:
            content.remove(impl);
        }
    }

    private class SaveCookieImpl implements SaveCookie {

        @Override
        public void save() throws IOException {

           Confirmation message = new NotifyDescriptor.Confirmation("Do you want to save \""
                    + jTextField1.getText() + " (" + jTextField2.getText() + ")\"?",
                    NotifyDescriptor.OK_CANCEL_OPTION,
                    NotifyDescriptor.QUESTION_MESSAGE);

            Object result = DialogDisplayer.getDefault().notify(message);
            //When user clicks "Yes", indicating they really want to save,
            //we need to disable the Save action,
            //so that it will only be usable when the next change is made
            //to the JTextArea:
            if (NotifyDescriptor.YES_OPTION.equals(result)) {
                fire(false);
                //Implement your save functionality here.
            }
        }
    }
</pre>
        <p><li>Run the application and notice the enablement/disablement of the
        Save button:

                      <p><img alt="enabled save button" src="../images/tutorials/crud/68dbmanager-992.png"/></p>

<p class="tips"> Right now, nothing happens when you click OK in the dialog
 above. In the next step, we add some JPA code for handling persistence of
 our changes.

        <p><li>Next, we add JPA code for persisting our change.
         Do so by replacing the comment "//Implement your save functionality here."
         The comment should be replaced by all of the following:

<pre class="examplecode">EntityManager entityManager = Persistence.createEntityManagerFactory("CustomerLibraryPU").createEntityManager();
entityManager.getTransaction().begin();
Customer c = entityManager.find(Customer.class, customer.getCustomerId());
c.setName(jTextField1.getText());
c.setCity(jTextField2.getText());
entityManager.getTransaction().commit();</pre>

<p class="tips"> The "customer" in <tt>customer.getCustomerId()()</tt> is currently undefined. Add the line
 in bold in the <tt>resultChanged</tt> below, after declaring <tt>Customer customer;</tt> at the top
 of the class, so that the current <tt>Customer</tt> object sets the <tt>customer</tt>,
 which is then used in the persistence code above to obtain the ID of
 the current <tt>Customer</tt> object.

<pre class="examplecode">@Override
public void resultChanged(LookupEvent lookupEvent) {
    Lookup.Result r = (Lookup.Result) lookupEvent.getSource();
    Collection&lt;Customer&gt; c = r.allInstances();
    if (!c.isEmpty()) {
        for (Customer customer : c) {
            <b>customer = cust;</b>
            jTextField1.setText(customer.getName());
            jTextField2.setText(customer.getCity());
        }
    } else {
        jTextField1.setText("[no name]");
        jTextField2.setText("[no city]");
    }
}</pre>

 <p><li>Run the application and change some data. Currently, we have no "Refresh"
  functionality (that will be added in the next step) so, to see the changed data, restart the application. Here, for
 example, the tree hierarchy shows the persisted customer name for "Toyota Motor Co":

                      <p><img alt="changed database" src="../images/tutorials/crud/68dbmanager-993.png"/></p>

        </ul>


 <li>Fourthly, we need to
  add functionality for refreshing the Customer viewer. You might want to
  add a <tt>Timer</tt> which periodically refreshes the viewer.
  However, in this example, we will add
  a "Refresh" menu item to the Root node so that the user will be able
  to manually refresh the viewer.
<ul>
        <li>In the main package of the <tt>CustomerViewer</tt> module,
         create a new <tt>Node</tt>, which will replace the <tt>AbstractNode</tt>
         that we are currently using as the root of the children in the 
         viewer. Note that we also bind a "Refresh" action to our
         new root node.

<pre class="examplecode">public class CustomerRootNode extends AbstractNode {

    public CustomerRootNode(Children kids) {
        super(kids);
        setDisplayName("Root");
    }

    @Override
    public Action[] getActions(boolean context) {
        Action[] result = new Action[]{
            new RefreshAction()};
        return result;
    }

    private final class RefreshAction extends AbstractAction {

        public RefreshAction() {
            putValue(Action.NAME, "Refresh");
        }

        public void actionPerformed(ActionEvent e) {
            CustomerTopComponent.refreshNode();
        }
    }

}</pre>

<p><li>Add this method to the <tt>CustomerTopComponent</tt>, for refreshing
 the view:

<pre class="examplecode">public static void refreshNode() {
    EntityManager entityManager = Persistence.createEntityManagerFactory("CustomerLibraryPU").createEntityManager();
    Query query = entityManager.createQuery("SELECT c FROM Customer c");
    List&lt;Customer&gt; resultList = query.getResultList();
    em.setRootContext(new <b>CustomerRootNode</b>(Children.create(new CustomerChildFactory(resultList), true)));
} </pre>


<p>Now replace the code above in the constructor
 of the <tt>CustomerTopComponent</tt> with a call to the above. As
 you can see in the highlighted part above, we are now using our <tt>CustomerRootNode</tt> instead
 of the <tt>AbstractNode</tt>. The <tt>CustomerRootNode</tt> includes
 the "Refresh" action, which calls the code above.

<p><li>In your save functionality, add the call to the method above so that,
             whenever data is saved, an automatic refresh takes place. You can
             take different approaches when implementing this extension to
             the save functionality. For example, you might want to create a
             new module that contains the refresh action. That module would
             then be shared between the viewer module and the editor module,
             providing functionality that is common to both.

 <p><li>Run the application again and notice that you have a new root node,
 with a "Refresh" action:

                      <p><img alt="new root node" src="../images/tutorials/crud/68dbmanager-994.png"/></p>

 <p><li>Make a change to some data, save it, invoke the Refresh action, and notice
  that the viewer is updated.

        </ul>
    </ol>
        <p>You have now learned how to let the NetBeans Platform handle changes
         to the <tt>JTextFields</tt>. Whenever the text changes, the NetBeans
         Platform Undo and Redo buttons are enabled or disabled. Also, the
         Save button is enabled and disabled correctly, letting the user
         save changed data back to the database.

    <h3 class="tutorial"><a name="create"></a>Create</h3>
    <p>In this section, you allow the user to create a new entry in the database.
    <ol>
        <li>Right-click the <tt>CustomerEditor</tt>
         module and choose "New Action".
         Use the New Action wizard to create a new "Always Enabled" action. The new
         action should be displayed anywhere in the toolbar and/or anywhere in
        the menu bar. In the next step of the wizard, call the action <tt>NewAction</tt>.

         <p class="tips">Make sure that
         you have a 16x16 icon available, which the wizard forces
         you to select if you indicate that you want the
         action to be invoked from the toolbar.</p>
        <P><li>In the New action, let the <tt>TopComponent</tt> be opened,
         together with emptied <tt>JTextFields</tt>:

<pre class="examplecode">import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public final class NewAction implements ActionListener {

    public void actionPerformed(ActionEvent e) {
        EditorTopComponent tc = EditorTopComponent.getDefault();
        tc.resetFields();
        tc.open();
        tc.requestActive();
    }

}</pre>

         <p class="tips">The action implements the <tt>ActionListener</tt> class, which
          is bound to the application via entries in the layer file, put there
          by the New Action wizard. Imagine how easy it will be when you
          port your existing Swing application to the NetBeans Platform, since
          you'll simply be able to use the same <tt>Action</tt> classes that you
          used in your original application, without needing to rewrite them
          to conform to <tt>Action</tt> classes provided by the NetBeans Platform!</p>


<p>In the <tt>EditorTopComponent</tt>, add the following method for resetting
 the <tt>JTextFields</tt> and creating a new <tt>Customer</tt> object:

<pre class="examplecode">public void resetFields() {
    customer = new Customer();
    jTextField1.setText("");
    jTextField2.setText("");
}</pre>

        <p><li>In the <tt>SaveCookie</tt>, ensure that a return of <tt>null</tt>
         indicates that a new entry is saved, instead of an existing entry
         being updated:

<pre>public void save() throws IOException {

    Confirmation message = new NotifyDescriptor.Confirmation("Do you want to save \""
                    + jTextField1.getText() + " (" + jTextField2.getText() + ")\"?",
                    NotifyDescriptor.OK_CANCEL_OPTION,
                    NotifyDescriptor.QUESTION_MESSAGE);

    Object result = DialogDisplayer.getDefault().notify(msg);

    //When user clicks "Yes", indicating they really want to save,
    //we need to disable the Save button and Save menu item,
    //so that it will only be usable when the next change is made
    //to the text field:
    if (NotifyDescriptor.YES_OPTION.equals(result)) {
        fire(false);
        EntityManager entityManager = Persistence.createEntityManagerFactory("CustomerLibraryPU").createEntityManager();
        entityManager.getTransaction().begin();
        <b>if (customer.getCustomerId() != null)</b> {
            Customer c = entityManager.find(Customer.class, cude.getCustomerId());
            c.setName(jTextField1.getText());
            c.setCity(jTextField2.getText());
            entityManager.getTransaction().commit();
        } else {
            <b>Query query = entityManager.createQuery("SELECT c FROM Customer c");
            List&lt;Customer&gt; resultList = query.getResultList();
            customer.setCustomerId(resultList.size()+1);
            customer.setName(jTextField1.getText());
            customer.setCity(jTextField2.getText());
            //add more fields that will populate all the other columns in the table!
            entityManager.persist(customer);
            entityManager.getTransaction().commit();</b>
        }
    }

}</pre>

<p><li>Run the application again and add a new customer to the database.

    </ol>

    <h3 class="tutorial"><a name="delete"></a>Delete</h3>
    <p>In this section, let the user delete a selected entry in the database. Using
     the concepts and code outlined above, implement the Delete action yourself.
    <ol>
        <li>Create a new action, <tt>DeleteAction</tt>. Decide whether you
         want to bind it to a Customer node or whether you'd rather bind it
         to the toolbar, the menu bar, keyboard shortcut, or combinations of
         these. Depending on where you want to bind
         it, you will need to use a different approach in your code. Read the
         tutorial again for help, especially by looking at how the "New" action
         was created, while comparing it to the "Refresh" action on the root
         node.
        <p><li>Get the current <tt>Customer</tt> object, return an 'Are you sure?' dialog,
         and then delete the entry. For help on this point, read the tutorial
         again, focusing on the part where the "Save" functionality is implemented.
         Instead of saving, you now want to delete an entry from the database.
    </ol>

</div>


    <!-- ======================================================================================== -->
    

    <h2><a name="nextsteps"></a>See Also</h2>

    <p>This concludes the NetBeans Platform CRUD Tutorial. This document has described
    how to create a new NetBeans Platform application with CRUD functionality for
    a given database.
    For more information about creating and developing applications, see the following resources:
    <ul>
        <li><a href="https://netbeans.org/kb/trails/platform.html">NetBeans Platform Learning Trail</a></li>
        <li><a href="http://bits.netbeans.org/dev/javadoc/">NetBeans API Javadoc</a></li>
    </ul>

    <!-- ======================================================================================== -->
    
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