Customizing Generation with GTL

The PowerDesigner Generation Template Language (GTL) is used to extract model object properties as text. GTL is written in templates and generated files defined under metaclasses in language definition and extension files. It powers generation of code for business process, object-oriented and XML languages, and can be used to define new generations for any model.

When you launch a generation from a model, PowerDesigner generates a file for each instance of each metaclass for which you have defined a generated file (see Generated Files (Profile)) by evaluating the templates it calls and resolving any variables.

GTL is object-oriented, supporting inheritance and polymorphism for reusability and maintainability, and provides macros for testing variables and iterating through collections, etc.

• Creating a Template and a Generated File
  GTL templates are commonly used for generating files. If your template is going to be used in generation, it must be referenced in a generated file.
• Extracting Object Properties
  Object properties are referenced as variables and enclosed between percent signs: %variable%. Variable names are case sensitive, and property names are, by convention, defined in CamelCase.
• Accessing Collections of Sub-Objects or Related Objects
  An OOM contains a collection of classes and classes contain collections of attributes and operations. To iterate over a collection, use the .foreach_item macro.
• Formatting Your Output
  You can change the formatting of variables by embedding formatting options in variable syntax. New lines and tabs are specified using the \n and \t escape sequences respectively.
• Conditional Blocks
  Place text containing a variable between square brackets to have it appear only if the variable resolves to a non-null value.
• Accessing Global Variables
  You can insert information such as your user name and the current date with global variables.
• GTL Operators
  GTL supports standard arithmetic and logical operators along with some advanced template operators.
• Translation Scope
  The initial scope of a template is always the metaclass on which it is defined. All standard and extended attributes, collections, and templates defined on the active object metaclass and its parents are visible, but only one object is active at any given time.
• Shortcut Translation
  Shortcuts are dereferenced during translation, so that the scope of the target object replaces the scope of the shortcut. This is different from VB Script where shortcut translation retrieves the shortcut itself. You can use the %IsShortcut% variable to test whether an object is a shortcut, and the Shortcut keyword to access the properties of the shortcut itself.
• Escape Sequences
  GTL supports a number of escape sequences to simplify the layout of your templates and generated files, and to make reserved characters accessible.
• Calling Templates
  You can call a template from a generated file or from another template by entering its name surrounded by percentage signs. Object properties, collections, and local and global variables are called in the same way. At generation time, a template call is replaced by the template content, which is then resolved to its final textual value.
• GTL-Specific Metamodel Extensions
  A number of calculated attributes and collections are provided as GTL-specific extensions to the metamodel.
• GTL Macro Reference
  GTL supports macros to express template logic, and to loop on object collections. Macro keywords are prefixed by a . (dot) character, which must be the first non-blank character in the line, and you must respect the use of line breaks in the macro syntax.
• GTL Syntax and Translation Errors
  Error messages stop the generation of the file in which errors have been found, these errors are displayed in the Preview tab of the corresponding object property sheet.