View source for EDT:Tutorial: RUI With DataBase Lesson 8

[[EDT:Tutorial: Access a database with EGL Rich UI|Access a database with EGL Rich UI]]


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= Lesson 8: Add variables and functions to the Rich UI handler =

Add source code that supports the user interface.In lessons 8 and 9, you update the EGL source code directly
and review changes in the Preview tab.

== Add code to support the data grid ==

Change the declaration of the data grid for two purposes: to
cause the web page to react when the user selects a cell and to ensure
that the grid output is formatted correctly.

<ol><li>In Project Explorer, open '''PaymentClient''' &gt; '''EGLSource''' &gt; '''handlers''' and double-click '''PaymentFileMaintenance.egl'''.
<li>Click on the Source tab.
</ol>

Make the following changes, ignoring the error marks: 

In the '''allPayments_ui''' DataGrid declaration,
add the following code immediately before the '''columns''' property: 
   selectionListeners ::= cellClicked, 
The '''selectionListeners''' property
specifies one or more functions that are called whenever the user
selects a cell in the grid. In this case, you are appending a function
name to a pre-existing array. You will write the '''cellClicked''' function
later in this lesson.

Formatters are functions that change the appearance of
the values in DataGrid columns. To demonstrate the feature, find the
DataGridColumn declaration for category. To ensure that the user sees
a category description rather than an integer, add this code after '''width=90''': 
   , formatters = [ formatCategory ]
When you display dollar amounts in a column, you typically
right-align the values. You do not need to code a function to cause
right-alignment. Instead, add this code after the '''width''' entry
for amount:
   , alignment = DataGridLib.ALIGN_RIGHT
The '''allPayments_ui''' declaration
is now as follows, with error marks for '''cellClicked''' and '''formatCategory''': 
      allPayments_ui DataGrid{
         layoutData = new GridLayoutData{
                          row = 2, column = 1,
                          verticalAlignment = GridLayoutLib.VALIGN_TOP},
         selectionListeners ::= cellClicked,
         columns =[
            new DataGridColumn{name = "category", displayName = "Type", 
                               width = 90, formatters = [ formatCategory ]},
            new DataGridColumn{name = "description", displayName = "Description", 
                               width = 120},
            new DataGridColumn{name = "amount", displayName = "Amount due", 
                               width = 90, alignment = DataGridLib.ALIGN_RIGHT}
         ], 
         data = allPayments as any[],
         selectionMode = DataGridLib.SINGLE_SELECTION};

Save the file before going on to the next step.

== Code the function that responds when the user clicks the data grid ==

The '''cellClicked''' function is invoked when
the user clicks a cell in the data grid.

Immediately below the '''start''' function,
add the following lines:
   function cellClicked(myGrid DataGrid in)
      selectedPayment = allPayments_ui.getSelection()[1] as paymentRec;
      selectedPayment_form.publish();
   end

First, the '''cellClicked''' function
updates the '''selectedPayment''' record with data from
a single data-grid row. That row can include more fields than are
displayed to the user. In this application, the single row in the
data grid will have come from a single row in the database.

Second,
the '''publish''' function causes the transfer
of data from the '''selectedPayment''' record to the '''selectedPayment_ui''' layout.
That transfer is made possible by code that was provided for you when
you created the '''selectedPayment_ui''' layout, which
is the single-record layout at the right of your web page. If you
review the code, you can trace the relationships:Â 

<ul><li>A Form Manager declaration includes form fields. 
<li>Each form field references a controller declaration.
<li>The controller declaration relates a model to a view; in this
case, a field of the '''selectedPayment''' record to a
child of the '''selectedPayment_ui''' layout.
</ul>

The Form Manager provides various benefits but is essentially
a collection of controllers.

Here is an explanation of two other
issues&quot;”the use of the bracketed array index ('''[1]'''),
and the use of the '''as''' operator:

<ol><li>The '''getSelection''' function always returns
a subset of the rows in the '''data''' array of
the data grid. However, when you declared the data grid, you specified
the following setting to indicate that the user can select only one
row at a time: '''selectionMode = DataGridLib.SINGLE_SELECTION'''.
When the user can select only one row, only one element is available.
<li>Every element in the array returned by a '''getSelection''' function
is of type ANY. You typically use the same Record part to process
input to the grid and to process output from the grid, and in this
tutorial, the Record part is '''paymentRec'''. The Record
part has the following uses:
</ol>
:*To be the basis of the array elements that you assign to the '''data''' property of the data grid, as shown in the following setting:
   data = allPayments as any[]
:*To cast the array element that is returned by the '''getSelection''' function of the data grid, as shown here:
   allPayments_ui.getSelection()[1] as paymentRec 

In each case, the '''as''' clause provides
the necessary cast.

== Format column values in the grid ==

To add the formatter function:

*Add the following code before the final '''end''' statement in the file: 
   function formatCategory(class string, value string, rowData any in)
      value = PaymentLib.getCategoryDesc(value as INT);
   end
:Formatters have the parameters shown. In this case, the formatter wraps a library function you created earlier.
*Press Ctrl-Shift-O to organize the required import statements and save the file. All the error marks disappear.

== Test the formatting of the data grid and the transfer of data to the single-record layout ==

You can test your recent changes even before you gain
access to the database.

*Click the Preview tab and note that the categories are now descriptions (for example, '''Rent''' rather than '''1'''). [[Image:EDT_Tutorial_edt_richui_sql08_formatted_grid.jpg|The formatted data grid]]
*Click one or another row in the data grid and note that the single-row layout is updated appropriately. However, the formatter affected only the data grid, and the description field in the single-row layout contains a numeric. The tutorial will address that issue later.
*Click the Source tab and change the '''start''' function so that the first record in the prototype data includes a value for '''payeeName''', which is a '''paymentRec''' record field that is not displayed by the data grid:  
   function start()
      allPayments_ui.data =[
      new paymentRec{
         category = 1, description = "test01", amount = 100.00
         ''' , payeeName = "Someone" '''},
      new paymentRec{category = 2, description = "test02", amount = 200.00},
      new paymentRec{category = 3, description = "test03", amount = 300.00}];
   end
*Click the Preview tab and click the first row in the data grid. [[Image:EDT_Tutorial_edt_richui_sql08_prototype_and_all_plus.jpg|The data transferred from data grid to the single-record layout]]

As shown, you can switch quickly from one tab in the Rich
UI editor to another, to test even a small change.

== Comment the prototype data ==

You can comment or uncomment code quickly, as shown in this
step.

*Click the Source tab.
*In the '''start''' function, select the complete assignment statement, right-click the area selected, and click '''EGLSource > Toggle Comment'''. [[Image:EDT_Tutorial_edt_richui_sql08_toggle_comments.jpg|The selection of code and the Comment menu item]]
*Comment marks (//) are now at the start of each line. You could remove the comments by selecting the commented statements and repeating the task. However, leave the comments in place.  EGL also supports the use of slash asterisk (/*) and asterisk slash (*/) delimiters, as shown here: 
   /* 
       You can add comments in either of two ways. 
   */

== Declare a service-access variable ==

You now declare a service-access variable, which will
let you communicate with the service that you defined earlier.

To create the variable:

*Near the top of the EGL source code, find the handler declaration for '''PaymentFileMaintenance'''. Add a blank line, and immediately before the '''ui''' GridLayout declaration, add the following statement:
   dbService SQLService?{@dedicatedService};
:The '''@dedicatedService''' property indicates that the service being referenced is a dedicated service, which will be deployed with the Rich UI handler. 

:In the following display, the red X in the margin indicates a problem in the code: [[Image:EDT_Tutorial_edt_richui_sql08_red_x.jpg|The declaration of the service-access variable, in code]]

:To see the error message, move the cursor over the X.

*Fix the '''unresolved type''' error by pressing Ctrl+Shift+O. The new '''import''' statement provides access to the '''services''' package, '''SQLService''' part, which is in the '''PaymentService''' project. The reference to '''SQLService''' is resolved because that project is on the EGL build path of the '''PaymentClient''' project.
*Save the file. 

== Create functions that use the service-access variable to invoke the service ==

You now create several functions to invoke different functions
in the dedicated service. Once you understand how to set up one invocation,
the others are straightforward.

First add a service exception handler and logging functions prior to the final '''end''' statement.   Include the following code:
   function serviceExceptionHandler(ex anyException)
        try
            throw ex;
        onException(serviceEx ServiceInvocationException)
            log("Failure:  service invocation, exception = " +
                            serviceEx.message);
            log("Detail 1:  " + serviceEx.detail1);
            log("Detail 2:  " + serviceEx.detail2);
            log("Detail 3:  " + serviceEx.detail3);
        onException(anyex anyException)
            log("Failure:  service invocation, exception = " + anyex.message);
        end
        throw ex;
   end
   
   logActive boolean = true;
   
   function log(text string in)
        if(logActive)
            sysLib.writeStderr(text);
        end
   end

Then include the function that reads all data from the table.  Leave a blank line after the ''cellClicked''' function and add the following code:    
   function readFromTable()
      call dbService.getAllPayments() returning to updateAll
         onException serviceExceptionHandler;
   end

'''Notes:''' 
<ol><li>The '''call''' statement in Rich UI is a variation
used only to access services. The runtime communication in this case
is asynchronous, which means that the user can continue to interact
with the handler while the service is responding.
<li>The asynchronous '''call''' statement includes
two function names:

<ul><li>'''updateAll'''
<li>'''serviceExceptionHandler'''
</ul>

The two are ''callback functions'', which are invoked
by the EGL runtime code after the service responds or fails. If the
service returns a value successfully, the '''updateAll''' function
is invoked. If the call fails, the EGL runtime code invokes the function
named '''serviceExceptionHandler'''. 

Our example exception handler function just displays the exception messages
in the display of error information in the
at the bottom of the web page
(at run time). However, you would typically an error handler of your own that might log the error information, but display a message to the user saying something like &quot;Your request cannot be completed at this time.&quot; 
</ol>
Now, to create the '''updateAll''' callback function, click anywhere in the '''call''' statement,
right-click, and click '''Create Callback Functions'''.
Alternatively, you could clicked anywhere in the statement, held down
the Ctrl key, and pressed 1. [[Image:EDT_Tutorial_edt_richui_sql08_callback.jpg|The Create Callback Functions option]]
EGL creates an empty '''updateAll''' function.
An error handler would have been created as well if you had not already included a function named '''serviceExceptionHandler''' in the program.

The
parameter list in the created '''updateAll''' function
is equivalent to the type of return value that is expected from the
service. Here are the relationships that explain the behavior of the
Rich UI editor:

<ul><li>The parameter list in the callback function is correct because
the '''getAllPayments''' function in the Service part is
available to the editor.
<li>The function is available because you resolved the reference to
the '''SQLService''' part in a previous step.
</ul>
 
Next, create the function that adds sample data.  Click Ctrl-F to gain access to the Find/Replace dialog,
type '''SampleData''', and click '''Find'''.
Update the '''sampleData''' function so that
the code is as follows:
   function sampleData(event Event in)
      call dbService.createDefaultTable() returning to updateAll
         onException serviceExceptionHandler;
   end
You do not use the '''Create Callback Functions''' feature
because the callback functions exist. 

Next, create the function that adds data.   Update the '''addRow''' function so that the
code is as follows: 
   function addRow(event Event in)
      call dbService.addPayment(new paymentRec) returning to recordAdded
         onException serviceLib.serviceExceptionHandler;
   end
Click anywhere in the '''call''' statement,
right-click, and click '''Create Callback Functions'''. EGL adds the '''recordAdded''' function. 

Now create the function that deletes data.  Update the '''deleteRow''' function so that
the code is as follows: 
   function deleteRow(event Event in)
      for(i INT from 1 to allPayments.getSize()) 
         if (allPayments[i].paymentID == selectedPayment.paymentID)
            allPayments.removeElement(i);
            exit for;
         end
      end
      call dbService.deletePayment(selectedPayment) returning to recordRevised
         onException  serviceExceptionHandler;
   end

The function acts as follows:
<ul><li>Deletes the selected row from the local array of records
<li>Calls the database service to delete the row from the database
itself
</ul>

Now click anywhere in the '''call''' statement,
right-click, and click '''Create Callback Functions'''. EGL adds the '''recordRevised''' function.

To complete this step,
<ul>
<li>Press Ctrl-Shift-F to format the code.
<li>Save the file.
</ul>
''' Related information '''<br>
[../../com.ibm.egl.pg.doc/topics/pegl_ui_richui_rest_call_statement.html Invoking a service asynchronously from a Rich UI application]

== Update the start function to initialize the data grid with database rows ==

To initialize the data grid, add the following code before
the '''end''' statement of the '''start''' function:
  readFromTable();
Although
you could have assigned the '''readFromTable''' function
directly to the '''onConstructionFunction''' property,
you are advised to retain the '''start''' function as a
separate unit of logic in case you later decide to add other code
that runs before the web page is rendered.

Retain the commented
code in the '''start''' function in case you need to test
the web page without accessing the database. You can use the comment
and uncomment capability of the Rich UI editor to quickly switch from
the function call to the prototype data and back again.

== Complete the callback functions ==

You now complete the callback functions that were created
automatically:

<ul><li>'''updateAll'''
<li>'''recordAdded'''
<li>'''recordRevised'''
</ul>

The '''updateAll''' function receives an array
of '''paymentRec''' records from the dedicated service.
The function is called in the following ways:

<ul><li>As a callback function at startup, after the '''readFromTable''' function
calls the service.
<li>As a callback function whenever the user clicks the '''Sample''' button
to invoke the '''sampleData''' function.
</ul>

Update the '''updateAll''' function so that
the code is as follows: 
   function updateAll(retResult paymentRec[] in)
      allPayments = retResult;
      allPayments_ui.data = allPayments as any[];
   end
The function updates the global
array of payment records with the data received from the service and
then refreshes the data grid.

The '''recordAdded''' function receives the
record that was sent to and returned by the service function '''addPayment'''. Update the '''recordAdded''' function so that
the code is as follows: 
   function recordAdded()
      readFromTable();
   end
The function '''readFromTable''' reads
all the rows from the database. The data stored by the grid can then
contain the new row, including the '''paymentID''' value
that was automatically generated by the database and that is otherwise
unavailable to the grid. 

The '''recordRevised''' function receives
the record that was sent to and returned by the service function '''addPayment'''.Update the '''recordRevised''' function so that
the code is as follows: 
   function recordRevised()
      allPayments_ui.data = allPayments as any[];
   end
The function refreshes the data grid.

Clean up this step by formatting your code and saving the file.
If you see errors
in your source file, compare your code to the file contents in [[EDT:Tutorial: RUI With DataBase Lesson 8 Code|Code for PaymentLib.egl after lesson 8]].

== Test the interface ==

Preview your work now that you are accessing a database.

<ol><li>Click the Preview tab. The data grid has
no content because you commented out the prototype data, and the database
has no rows.[[Image:EDT_Tutorial_edt_richui_sql08_initial_ui.jpg|The initial data grid]]

<li>Click '''Sample''' to create sample data. 
<li>If EGL requests a password, enter '''admin''' for
both the '''User ID''' and '''Password''' fields.
Select '''Remember my user ID...''' and click '''OK'''.<br /> [[Image:EDT_Tutorial_edt_richui_sql08_pwd.jpg|The ID and password window]]

If you exit and restart the workbench
before you complete this tutorial, this window might be re-displayed
the next time you attempt to access the database.
Eventually
the grid is re-displayed with rows of sample data.<br /> [[Image:EDT_Tutorial_edt_richui_sql08_sample_data.jpg|Three payment entries, &quot;œApartment,&quot;? &quot;œGroceries,&quot;? and &quot;œISP&quot;? are displayed]]

<li>Click the '''Add''' button.  A new row with a single default value is displayed at
the bottom of the grid.<br />[[Image:EDT_Tutorial_edt_richui_sql08_added.jpg|A new row is added]]

<li>Select the Apartment row and click '''Delete'''. The row is deleted from both the display and the database.<br /> [[Image:EDT_Tutorial_edt_richui_sql08_deleted.jpg|The &#34;Apartment&#34; row is now gone.]]

<li>Click the first row of the data grid. <br />  [[Image:EDT_Tutorial_edt_richui_sql08_transfer_database.jpg|The data grid and single-record layout both contain data from the database.]]
Data from the database was transferred
from the data grid to the single-record layout. Note that the value
of the '''Key''' field reflects how many rows were
added to the database and will probably not match the value on your
web page.
</ol>

== Lesson checkpoint ==

You learned how to complete the following tasks:

<ul><li>To create formatters.
<li>To respond to the user's selection in a data grid.
<li>To transfer data from the data grid to a grid layout.
<li>To comment and uncomment code.
<li>To access services from a Rich UI application.
</ul>

In the next lesson, you will complete the code for the Rich
UI handler.

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