Go Template Syntax Guide

Fundamentals of Go template syntax for dynamic content generation in DataMagik Document Designer.

Table of Contents

1. Basic Variable Substitution
2. Nested Object Access
3. Array Access
4. Comments
5. Whitespace Control
6. Pipeline Operations
7. Variables in Templates
8. Complete Example

1. Basic Variable Substitution

Access data fields using dot notation with double curly braces:

<h1>{{.Title}}</h1>
<p>{{.Description}}</p>
<span>{{.Amount}}</span>

Multiple variables in one line:

<p>Hello {{.FirstName}} {{.LastName}}, your balance is ${{.Balance}}</p>

2. Nested Object Access

Use dot notation to access nested object properties:

<h2>{{.Customer.Name}}</h2>
<p>Email: {{.Customer.Email}}</p>
<p>{{.Customer.Address.Street}}</p>
<p>{{.Customer.Address.City}}, {{.Customer.Address.State}} {{.Customer.Address.Zip}}</p>

Deep nesting:

<p>Shipped to: {{.Order.Shipping.Recipient.Name}}</p>
<p>Tracking: {{.Order.Shipping.TrackingNumber}}</p>

3. Array Access

Direct Index Access

<p>First item: {{index .Items 0}}</p>
<p>Second item: {{index .Items 1}}</p>

Accessing Array of Objects

<p>First customer: {{(index .Customers 0).Name}}</p>
<p>First customer email: {{(index .Customers 0).Email}}</p>

4. Comments

Comments are not rendered in the output:

{{/* This is a comment and won't appear in output */}}
<p>{{.Message}}</p>

{{/* Multi-line comment
   It can span multiple lines
   and won't appear in the output */}}

{{/* Customer Information Section */}}
<div class="customer-info">
  {{/* Display customer name */}}
  <h2>{{.Customer.Name}}</h2>
</div>

5. Whitespace Control

Control whitespace around template tags using - trim markers:

<!-- Default: whitespace preserved -->
<p>  {{.Name}}</p>

<!-- Trim before: {{- removes leading whitespace -->
<p>  {{- .Name}}</p>

<!-- Trim after: -}} removes trailing whitespace -->
<p>  {{.Name -}}</p>

<!-- Trim both sides -->
<ul>
  {{- range .Items}}
  <li>{{- .Name -}}</li>
  {{- end}}
</ul>

6. Pipeline Operations

Chain operations using the pipe operator |:

<!-- Case conversion -->
<p>{{.Name | upper}}</p>
<p>{{.Description | lower}}</p>
<p>{{.Title | title}}</p>

<!-- Formatted output -->
<p>{{.Price | printf "%.2f"}}</p>
<p>{{.Date | dateFormat "January 2, 2006"}}</p>

<!-- Multiple pipes -->
<p>{{.Email | lower | printf "Contact: %s"}}</p>

7. Variables in Templates

Declaring Variables

{{$total := .Amount}}
<p>Amount: ${{$total}}</p>

Variables in Loops

{{range $index, $item := .Products}}
<div>
  <p>{{$index}}. {{$item.Name}}</p>
  <p>Price: ${{$item.Price}}</p>
</div>
{{end}}

Capturing Root Context

Save the current context to access it inside range or with blocks:

{{$root := .}}
{{range .Orders}}
<div>
  <p>Order: {{.Number}}</p>
  <p>Company: {{$root.CompanyName}}</p>
</div>
{{end}}

8. Complete Example: Invoice Template

<div class="header">
  <h1>{{.Company.Name | upper}}</h1>
  <p>{{.Company.Address.Street}}</p>
  <p>{{.Company.Address.City}}, {{.Company.Address.State}} {{.Company.Address.Zip}}</p>
</div>

<div class="details">
  <h2>Invoice #{{.InvoiceNumber}}</h2>
  <p>Date: {{.InvoiceDate | dateFormat "January 2, 2006"}}</p>
  <p>Due: {{.DueDate | dateFormat "January 2, 2006"}}</p>
</div>

<div class="customer">
  <h3>Bill To:</h3>
  <p>{{.Customer.Name}}</p>
  <p>{{.Customer.Email}}</p>
</div>

<table>
  <thead>
    <tr><th>Description</th><th>Qty</th><th>Price</th><th>Total</th></tr>
  </thead>
  <tbody>
    {{- range .Items}}
    <tr>
      <td>{{.Description}}</td>
      <td>{{.Quantity}}</td>
      <td>${{.Price | printf "%.2f"}}</td>
      <td>${{.Total | printf "%.2f"}}</td>
    </tr>
    {{- end}}
  </tbody>
</table>

<div class="total">
  <p>Subtotal: ${{.Subtotal | printf "%.2f"}}</p>
  <p>Tax ({{.TaxRate}}%): ${{.Tax | printf "%.2f"}}</p>
  <p>Total: ${{.TotalAmount | printf "%.2f"}}</p>
</div>

For more on string manipulation, see the String Functions Guide. For conditional logic, see the Control Flow Guide. For date formatting, see the Date & Time Functions Guide.

Related: Go Template Package - Official Go documentation