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ColdFusion: Article

Building Generic Maintenance Interfaces

Sparing yourself an awful lot of tedious work

When the March 2006 issue of CFDJ arrived, I had just begun working on the maintenance interfaces for the support tables of a new system. There are many of these tables, and implementing the associated maintenance routines looked set to consume a lot of time.

I had just finished implementing DAOs for the first of the support forms when I came across Nic Tunney's article on ObjectBreeze. ObjectBreeze was going to save me a lot of time on implementation - and spare me an awful lot of tedious work building DAOs for each table.

ObjectBreeze saved me so much time it got me to thinking… Would it be possible to implement the user interfaces generically, in the same way that ObjectBreeze implements our data model? And if we have a consistent, generic interface to access a data model, can we leverage that interface in the view and controller tiers too? The controller tier seems simple enough - for a simple maintenance form it merely needs to actuate the CRUD methods of the DAO. As far as the view tier goes, if it knew what the data model looked like, it shouldn't be difficult. The potential benefits would be enormous - I could concentrate my time on the difficult tasks of aggregating data and implementing business logic without worrying about data access or user interfaces.

Building the Basics
For this article we're going to put together a fictitious system for a hypothetical racing club. This club needs to track the drivers, teams, and cars that enter club races in various classes. Figure 1 details our data model. We have tables for each object - drivers, cars, teams, and classes. A car belongs to a single team, races in a single class, and is driven by a single driver. Drivers can drive any number of cars in different classes for different teams. Teams can own any number of cars, and classes can contain any number of cars.

Let's start with the drivers. They're one of the simplest objects because they don't contain any references to other objects (tables). The club is interested in tracking a driver's first and last name and his nationality. First we'll set up our controller (drivers.cfm). This will be the only file that the browser requests when manipulating a driver object. Our controller is essentially a switch statement that interprets a form parameter called controlMethod. Our controller supports the standard CRUD operations - create (add), read (edit), update, and delete operations, plus a list operation. Each operation involves a database operation and a user interface to render the results. The list operation will retrieve all of the drivers and display them in a grid, and the edit operation retrieves one driver and outs his details in a form for editing. Create is similar to edit except that it creates a new driver record. Update applies the results of a create or edit operation and delete removes a driver's data from the database. ObjectBreeze is used to handle the data model.

Each method that has to present data to the user also contains a call to the custom tag responsible for building the view. There's a tag for displaying lists (grid) and for editing a single record (detail). Since these templates are going to be generic, I've put them in a directory called genericUI. A CFMODULE call is used to invoke the generic code.

The Views
The maintenance for the drivers' table is a typical table maintenance application - a list of items and a detail form for editing an individual item. The generic grid template will display our list of items with controls to enable adding and deleting records, and a control to select an item for editing. To do this we have to tell the grid control which fields we want displayed, what the captions for those fields should be, and the data to be displayed. Using that information it's a pretty simple matter of looping over the list of captions to create the grid header. A two-dimensional loop displays the requested fields for each row of data.

The detail form is similar to the grid. For each field in the data model, we generate a table row containing a label and a textbox to edit the corresponding field. Arguments to our custom tag are similar to the grid except that we're passing a single data object.

See Listing 1 for the code we've built so far.

So how does it work? Not bad for a first stab. We've got a grid containing a list of drivers. We've got links for adding, editing, and deleting drivers. It definitely isn't perfect - there are a couple shortcomings we'll want to address. The first of these shortcomings is that the controller template is specific to the drivers' table. Before we can really reuse our code we'll want to build a generic controller template.

The Controller
Fortunately the task of converting the controller template is fairly simple. We want to call the controller as a custom tag, so instead of looking at form variables for our parameters we're going to be looking at attributes. We'll also have to tell the controller what fields we want displayed, and what their associated captions are. We'll also pass the form scope into the controller. Then we modify our custom tag calls to use these attributes instead of our hard-coded field lists. Our generic controller gets a new name - genericmasterdetail.cfm - and it moves into the genericUI folder.

The page that the browser invokes now becomes very simple - just a call to genericmasterdetail with the proper parameters. When we test our new drivers.cfm page in the browser, everything looks and functions exactly as before. Now we're ready to really leverage what we've built. The classes and team tables are both simple tables, similar in structure to the drivers' table. We make copies of the drivers.cfm file, change the parameters we pass to genericmasterdetail, and presto - fully functional maintenance forms for drivers, teams, and classes. I've done a little preprocessing to make things a bit neater. For example, I've included logic in classes.cfm to instruct our generic user interface to display only the class name during the list operation and all three fields during add or edit operations. See Listing 2 for the updated code.

Object Composition
The objects we've worked with so far are very simple in that all of the data they require is in one table. Usually, we're not that lucky; we often need data from multiple tables. ObjectBreeze supports models like these through composite objects. ObjectBreeze gives us a nice set of features for working with composite objects - we use the containsOne() or containsMany() methods to register the relationships between our tables with ObjectBreeze and it takes care of our database interactions for us.

Introducing composition into our generic user interfaces poses two problems. The first is how to tell the controller code to create a compound data object for us. The second is how to deal with this data in the user interface.

The second question is actually the easier of the two to answer. If we have a "contains one" relationship, such as the one between a team and a car, we can use a list box control to update that relationship. If we have a "contains many" relationship, we can use a cross-select to select the related items. Of course we'll have to know the relationship between the parent and children to know how to handle each item, but we have to describe that relationship to the controller to get the data objects configured properly in the first place.

XML to the Rescue
XML is the perfect choice for describing data to our generic user interfaces. It also makes it easy to enhance our code without making changes to the way it gets called. We're going to work with the racecars table for our first example. Cars are driven by a driver, entered in a class, and owned by a team. That is to say that there is a "contains one" relationship between our racecars object and the team, classes, and drivers objects.

The XML document that describes the racecars' object to genericmasterdetail is in Listing 3. The document describes the data model (datamodel element and children), the grid view (grid element), and the detail view (detail element). We'll feed this document into our genericmasterdetail custom tag and from there into the grid and detail custom tags. These tags have changed in several different ways. First, the arguments have changed. The form scope still gets passed into genericmasterdetail, grid, and detail but the configuration document has replaced the other arguments. All the references to the old arguments were updated to look at the configuration document instead. A new custom tag - uiformelements - has been created to handle the display of the individual form elements. Finally, two helper functions have been created to help us manage composite data access objects.

Listing 3 contains the racecars' XML document and the helper functions configureDAO() and getProperty().

All of these upgrades buy us a lot of functionality. We've moved quite a ways beyond simple forms. We can now add, update, and delete records in a wide variety of formats with just a few lines of XML.

More Stories By Craig Drabik

Craig Drabik is a senior programmer with the State University of New York at Buffalo. He is a Macromedia certified ColdFusion developer who has been working in ColdFusion since version 4.51.

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