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ColdFusion: Article

Model-Driven Development with ColdFusion and UML

Generating Code from Class Diagrams

The sign of an experienced developer is solid design. Novices edit examples they find on the Net, journeymen figure out how to code something as they do it, but craftsmen plan their work. Starting out, this can look like wasted time, but if your app is any good, your customer will want to expand it. Then, if you need some help, you'll have to explain all that intuitive code to ten people, all of whom you are paying by the hour. Diagrams would be nice then, right?

Many development organizations are moving toward more structured development cycles, involving formal documentation standards, to ensure that code is maintainable after the developer moves away from the project. For these organizations, the challenge is to balance the demand for rapid development with the requirement for clear, solid design and analysis documents.

For developers, it is annoying to go through the trouble of writing all of those class, property, method, and argument names only to have to do it again in the database and in the code. Wouldn't it be great to do that once and then fill in the details -- kind of sketch out the application - so that the model would drive the development and get developers enthusiastic about the whole process? In this article I'll illustrate how to do this by taking a UML class diagram and using it to generate ColdFusion code. From this simple starting point, one could go on to create stubs for complex CFCs, tables, stored procedures, unit tests and even simple CRUD GUIs.

A Picture Is Worth a Thousand Words
To start, we need to find a diagramming tool that is capable of exporting its diagrams in a text format. UML tools generally seem to be using XMI (XML Metadata Interchange) to handle this, and Gentleware's Poseidon Community Edition comes to our rescue as a capable, free editor. The downside is that XMI is pretty verbose. Diagram two or three classes and you're already clocking hundreds of lines of text. The upside is that it's XML, and with ColdFusion's XML functions for parsing and searching, we'll be able to tackle this with ease... after we figure out the format of that huge file. Now that we have a tool to edit our diagrams and save them to text, we can plan our application. We're writing a tool to generate code from diagrams, so let's start by diagramming. That way we'll have something to generate at the end of this article. We know that we'll have to do at least four things: parse the XMI; create a model of our results that is easy to manipulate; generate code based on the model; and, finally, do something with the generated code (write to a file, execute, etc.). These things are likely to be complicated enough that they will involve a set of functions, so, on our diagram, we'll create four classes to start with: XMI_Parser, Generator, Model, and Writer.

Parsing the XML
First we'll have to get our tool to export an XMI version of our diagram. In Poseidon, this is as simple as File->Export Project to XMI. Open up the diagram you created earlier and export it to XMI, then open it in a text editor or an XML editor. You will see, as you browse through the file, that there is a lot of layout markup that is irrelevant to us: We're only interested in 17 of this file's 660 lines! The XML will get more and more complex as we add functions, attributes and new datatypes. We will need to find the information that is relevant to our application design, then extract and simplify it to make it easier to work with for the rest of the project. (see Figure 1) This requires a function that wraps a series of XPath queries by way of ColdFusion's xmlSearch. We'll put that on our diagram as a public function in the XMI_Parser class as "createModelFromFile," which will take a string called fileName (the path to the XMI file) and return a Model object. Poseidon shows this as "+createModelFromFile(fileName:string):Model." For our purposes, we start by identifying classes used in the diagram:

      xmlDoc = xmlparse('OpenModel.xmi');
      classes = xmlsearch(xmlDoc,"//UML:Class[@xmi.id]");
      classesLen = arrayLen(classes);
      for(i=1;i lte classesLen;i=i+1){
        thisClass = classes[i];
        //now loop down into properties, methods and arguments

Deconstructing the XPath Query
Our XPath query for classes looks through the whole XML document for all elements of type UML:Class that have an xmi.id element ("[@xml.id]]"), regardless of their position in the document ("//"), and returns an array of ColdFusion XML objects that match. Listing 1 shows the XML element describing our XMI_Parser class at this point in the design.
We can see that we are interested in elements of type UML:Class that contain elements of type UML:Attribute and UML:Operation. UML:Operation elements also contain UML:Parameters, some of which are input (kind="in") and some of which are output (kind="return"). The subelements refer to other Classes or Datatypes for their type info: <UML:DataType xmi.idref = '1'/>. Somewhere in our diagram there is a Class or Datatype that has xmi.id = '1' to match this reference. These IDs are assigned by the tool to track the entities being diagrammed. When we want to determine an element's type (e.g, string, date, etc.), we can do an XPath query to look it up:

thisMethodReturnsDataType = xmlsearch(xmlDoc,"//*[@xmi.id='#thisMethod.returnParam_XMI_IDREF#']");

Creating the Model
You can see now what we have to do. We are going to loop over the results of the classes XPath query, building a ColdFusion structure as we go that simplifies and abstracts the XML we are reading. For each Class, we will loop over the nested Attributes (properties for us), then the Operations (functions for us). For each Operation, we will loop over its Parameters (arguments). At the end of the day, we have a ColdFusion structure that looks like this:

   name [string]
   displayname [string]
   hint [string]

        name [string]
        type [string]
        required [BOOLEAN]
        displayname [string]
        hint [string]
        default [string]
        string name [string]
        access [string]
        returntype [string]
        roles [string]
        hint [string]
        output [BOOLEAN]
            name [string]
            type [string]
            required [BOOLEAN
            default [string]
            hint [string]

To ensure that we have a consistent interface to this data structure, we'll add functions to our Model class to add or remove information. Let's update our diagram with: addComponent, deleteComponent, addProperty, deleteProperty, addMethod, deleteMethod, addArgument, and deleteArgument. We'll also add functions called getModel (to return our populated struct), serialize (in case we want to save our struct to a file for later use), and deserialize (to populate a Model from a previously saved state), as well as a private property called componentStruct to keep track of everything as we go.

More Stories By Chip Temm

Over the past decade, Chip Temm moved from North America to Europe and on to Africa where his company anthroLogik solutions provided analysis and development services organizations across seven timezones. He is currently back in Washington, DC where "remote development" means working from home and "wildlife" means raccoon.

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