Advanced Database Example

Advanced Database Example

This chapter will demonstrate advanced example of using ASP Express components to build web page for tables Vendors and Parts with support for master-detail data editing. We are going to use TASPXFindView, TASPXShoppingCartView, TASPXEditView, TASPXReconcileView and TASPXTabbedView components to develop application user interface.

The major goal of this sample is to explain the basic principles of implementing data retrieval and updates with ASP Express.

Create a new ActiveX Library project and add two MTS Data Modules in it. Save all project files in some directory using the following naming convention:

Put TADOConnection, two TADODataSet components, TDataSource, TXMLProvider and TXMLADOResolver on the design window of BusinessServices data module. Set their properties according to this table:

This is how your data module BusinessServices will look like after you have completed the instructions above:

Right-click VendorProvider component and select Save XML option. Enter Vendors in the Save As dialog and Vendors.XML file with Vendor-Parts data will be saved in the specified location. Set DB.Connected property to False.

BusinessServices component shell provide the following services for our application:

• Search against Vendors table;
• Retrieval of any particular Vendor information including all Parts supplied by this vendor;
• Method to save modifications of Vendors-Parts data to the database.

For both search and retrieval we are going to use the same Vendors, VendorSource and Parts components changing their properties accordingly to archive desired functionality.

Implement IBusinessServices.GetVendor method as shown below:

This method will return one Vendor record and all Parts which it supplies. 

Implement IBusinessServices.FindVendors as follows:

FindVendors performs case-insensitive search against Vendors table by VendorName and/or City fields. If neither parameter was provided then exception is raised. This method temporarily disconnects Parts dataset and the result of FindVendors will include located vendors only.

Implementation of IBusinessServices.SaveChanges method is almost trivial and pretty much the same for the majority of projects:

Next, you will build presentation services of application that will use methods GetVendor, FindVendor and SaveChanges.

Put TASPXEngine, TASPXPersistentSession, TASPXReconcileView, TXMLData and TASPXFindView components on the PresentationServices data module. Setup their properties:

Design form for the viewFindVendors component. Select viewFindVendors.Form property in Object Inspector and click on a (...) button to bring up Web Form Designer. 

Drag and drop two TLabelElement components, two TTextElement components and one TSubmitElement component on the form.  Set component properties according to the table:

This is how your form may look like:

Setup viewFindVendors.Columns property as follows:

Implement viewFindVendors.OnPerformFind event handler:

Implement IPresentationServices.DisplayFindVendors method ...

... and install both BusinessServices and PresentationServices components in package/application MyASPXSamples. Generate test ASP script to test IPresentationServices.DisplayFindVendors method using Page Wizard. Navigate to the script in a web browser and make sure that everything works fine:

On this phase we are going to provide user with a ability to place arbitrary vendors with their parts in some sort of a shopping cart. This will allow user to perform multiple searches against vendor database and maintain a list  of selected vendors at the same time.

When user clicks on a link in Find Vendors section a shopping cart component will retrieve picked vendor and corresponding  parts information from the database and preserve this data in user session. The shopping cart content will be displayed on the same page with Find Vendors section.  

Put TXMLData and TASPXShoppingCartView components on the PresentationServices data module. Setup their properties:

Build columns for viewVendorSC component:

Setup viewVendorsSC.ToolBar.Buttons collection:

Implement dataVendors.OnSessionInit and viewVendorsSC.OnPutItemInCar event handler and IPresentationServices.DisplayVendorCartAndFindSections interface method as explained below:

First event handler will initialize dataVendors with empty XML data packet upon UserSession request. Second event handler is called whenever viewVendorsSC detects that new Vendor record should be placed in vendors cart. New interface method will display shopping cart content and current state of find view if called from ASP script.

Create ASP script to test DisplayVendorCartAndFindSecitons using Page Wizard:

Navigate to the page in a web browser and play with it for awhile:

Shopping cart contains vendor and relates parts records that can be displayed in any other view-type components.

We don't have enough empty space on our latest version of User Interface to display more views. The common solution to this problem is to use another HTML page or implement tabbed presentation of information. Lets place TASPXTabbedView component on the PresentationServices data module. Change properties of this component as described below:

Add new interface method IPresentationServices.DisplayVendors:

Deploy a new ASP script that invokes IPresentationServices.DisplayVendors and try to switch between Find and Edit tabs, add vendors to shopping cart, etc. The page displayed below was build with Advanced template and includes demo menu.  

We have provided an extra Edit tab that can be used to link some other views to application presentation. Lets put TXMLData and two TASPXEditView components on the data module. Change their properties according to the table:

Setup viewEditVendors.Columns:

Setup viewEditVendors.Form as shown on the picture. Transform PreferredText1 into PreferredSelect1 and add two items to PreferredSelect1.Values: Yes and No. Then set VendorNoText1.ReadOnly to True.

Setup viewEditVendors.ToolBar.Buttons:

Setup viewEditParts.Columns:

Setup viewEditParts.Form. Set PartNoText1.ReadOnly  and VendorNoText2.ReadOnly property values to True.

Setup viewEditParts.ToolBar.Buttons:

Create viewEditVendors.OnApplyUpdates event handler to send Delta of changes to BusinessServices component for data resolving. This event handler will also perform error reconciliation:

Run application in a web browser and try to explore its reach features.

Switch to Edit tab...

... click on Techniques link...

.. then click Underwater Diver Vehicle link...

In this advanced example you've learned how to build web-enabled data entry screens that are accessible in modern forth generation browsers. Powerful data management of ASP Express enables transactional data updates with optimistic locking in multi-user environment. Built-in master-detail support makes a snap complex User Interface design.

While developing this example we have implemented several methods of IPresentationServices interface that expose different pieces of presentation logic incorporated in our component. We have been running this methods from different ASP scripts.

Marotz, Inc (C) 2000