Create a Custom Template

ADL comes with a library of built-in templates, but sometimes you need something specific to your project. This guide walks you through creating a custom Handlebars template from scratch.

What you’ll build

A simple template that generates a SQL CREATE TABLE statement for a data object. Along the way, you’ll learn the key Handlebars concepts you need to write your own templates for any output format.

Prerequisites

• An ADL project with at least one data object that has Data Items (columns) defined
• Familiarity with the basics of How ADL Works

Step 1: Create a new template

1. Navigate to the Templates screen.
2. Create a new template and give it a descriptive name, like “Simple Table DDL”.
3. The built-in code editor will open, ready for you to write your template.

Step 2: Write the basic structure

Start with the static parts — the SQL syntax that will be the same for every table:

CREATE TABLE [{{targetDataObject.name}}] (
);

The {{targetDataObject.name}} expression is a Handlebars placeholder. When ADL processes this template against a data object, it replaces this with the actual object name.

Step 3: Loop through columns

Now add the columns by looping through the Data Items:

CREATE TABLE [{{targetDataObject.name}}] (
{{#each targetDataObject.dataItems}}
  [{{name}}] {{dataType}}{{#unless isNullable}} NOT NULL{{/unless}}{{#unless @last}},{{/unless}}
{{/each}}
);

Here’s what each part does:

• {{#each targetDataObject.dataItems}} — Starts a loop over all columns in the data object.
• [{{name}}] — Outputs the column name in square brackets.
• {{dataType}} — Outputs the column’s data type.
• {{#unless isNullable}} NOT NULL{{/unless}} — Adds NOT NULL if the column doesn’t allow nulls.
• {{#unless @last}},{{/unless}} — Adds a comma after each column except the last one.
• {{/each}} — Ends the loop.

Step 4: Preview the output

1. Save your template.
2. Navigate to the Code Preview screen.
3. Select a data object and your new template.
4. Check the output — you should see a valid CREATE TABLE statement with all the columns from your data object.

Step 5: Enhance the template

Once the basics work, you can add more features:

Add a primary key

{{#if targetDataObject.businessKeyDefinitions}}
  CONSTRAINT [PK_{{targetDataObject.name}}] PRIMARY KEY (
  {{#each targetDataObject.businessKeyDefinitions}}
    [{{businessKeyComponentId}}]{{#unless @last}},{{/unless}}
  {{/each}}
  )
{{/if}}

Use helper functions

ADL provides custom Handlebars helpers for common operations. For example:

• {{stringReplace name "_" " "}} — Replace underscores with spaces
• {{now "yyyy-MM-dd"}} — Insert the current date
• {{lookupExtension targetDataObject.extensions "SchemaName"}} — Look up a custom extension value

Add conditional logic

{{#if targetDataObject.notes}}
-- {{targetDataObject.notes}}
{{/if}}

Step 6: Map and generate

Once you’re happy with the template:

1. Go to the Data Objects screen.
2. Select a data object and add a template mapping pointing to your new template.
3. Use the Code Generator to generate the output.

Tips for writing templates

• Start simple — Get the basic structure working before adding complexity.
• Preview often — The Code Preview screen is your best friend for testing templates.
• Study the built-in templates — They’re a great reference for common patterns and Handlebars techniques.
• Check the Handlebars Helpers — The custom helpers can save you a lot of effort.
• Keep templates focused — One template, one type of output. It’s easier to maintain several small templates than one giant one.

What’s next?

• Handlebars Helpers — Explore all the custom helper functions
• Template Library — Browse the built-in templates for inspiration
• Templates & Code Generation (Concepts) — Deeper dive into how the template system works