3.1_The template engine

The template engine

A type safe template engine based on Scala

Play comes with Twirl,
a powerful Scala-based template engine, whose design was inspired by ASP.NET Razor. Specifically it is:

compact, expressive, and fluid: it minimizes the number of characters and keystrokes required in a file,
and enables a fast, fluid coding workflow. Unlike most template syntaxes, you do not need to interrupt your coding to explicitly denote server blocks within your HTML. The parser is smart enough to infer this from your code. This enables a really compact and
expressive syntax which is clean, fast and fun to type.

easy to learn: it allows you to quickly become productive, with a minimum of concepts. You use simple
Scala constructs and all your existing HTML skills.

not a new language: we consciously chose not to create a new language. Instead we wanted to enable Scala
developers to use their existing Scala language skills, and deliver a template markup syntax that enables an awesome HTML construction workflow.

editable in any text editor: it doesn’t require a specific tool and enables you to be productive in
any plain old text editor.

Templates are compiled, so you will see any errors in your browser:

Overview

A Play Scala template is a simple text file that contains small blocks of Scala code. Templates can generate any text-based format, such as HTML, XML or CSV.

The template system has been designed to feel comfortable to those used to working with HTML, allowing front-end developers to easily work with the templates.

Templates are compiled as standard Scala functions, following a simple naming convention. If you create a

views/Application/index.scala.html

template
file, it will generate a

views.html.Application.index

class
that has an

apply()

method.

For example, here is a simple template:

@(customer: Customer, orders: List[Order])

<h1>Welcome @customer.name!</h1>

<ul>
@for(order <- orders) {
<li>@order.title</li>
}
</ul>

You can then call this from any Scala code as you would normally call a method on a class:

val content = views.html.Application.index(c, o)

Syntax: the magic ‘@’ character

The Scala template uses

@

as
the single special character. Every time this character is encountered, it indicates the beginning of a dynamic statement. You are not required to explicitly close the code block - the end of the dynamic statement will be inferred from your code:

Hello @customer.name!
^^^^^^^^^^^^^
Dynamic code

Because the template engine automatically detects the end of your code block by analysing your code, this syntax only supports simple statements. If you want to insert a multi-token statement, explicitly mark it using brackets:

Hello @(customer.firstName + customer.lastName)!
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Dynamic Code

You can also use curly brackets, to write a multi-statement block:

Hello @{val name = customer.firstName + customer.lastName; name}!
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Dynamic Code

Because

@

is
a special character, you’ll sometimes need to escape it. Do this by using

@@

:

My email is bob@@example.com

Template parameters

A template is like a function, so it needs parameters, which must be declared at the top of the template file:

@(customer: Customer, orders: List[Order])

You can also use default values for parameters:

@(title: String = "Home")

Or even several parameter groups:

@(title: String)(body: Html)

Iterating

You can use the

for

keyword,
in a pretty standard way:

<ul>
@for(p <- products) {
<li>@p.name ($@p.price)</li>
}
</ul>

Note: Make sure that

{

is
on the same line with

for

to
indicate that the expression continues to next line.

If-blocks

If-blocks are nothing special. Simply use Scala’s standard

if

statement:

@if(items.isEmpty) {
<h1>Nothing to display</h1>
} else {
<h1>@items.size items!</h1>
}

Declaring reusable blocks

You can create reusable code blocks:

@display(product: Product) = {
@product.name ($@product.price)
}

<ul>
@for(product <- products) {
@display(product)
}
</ul>

Note that you can also declare reusable pure code blocks:

@title(text: String) = @{
text.split(' ').map(_.capitalize).mkString(" ")
}

<h1>@title("hello world")</h1>

Note: Declaring code block this way in a template can be sometime useful but keep in mind that a template
is not the best place to write complex logic. It is often better to externalize these kind of code in a Scala class (that you can store under the

views/

package
as well if you want).

By convention a reusable block defined with a name starting with implicit will be marked as

implicit

:

@implicitFieldConstructor = @{ MyFieldConstructor() }

Declaring reusable values

You can define scoped values using the

defining

helper:

@defining(user.firstName + " " + user.lastName) { fullName =>
<div>Hello @fullName</div>
}

Import statements

You can import whatever you want at the beginning of your template (or sub-template):

@(customer: Customer, orders: List[Order])

@import utils._

...

To make an absolute resolution, use root prefix
in the import statement.

@import _root_.company.product.core._

If you have common imports, which you need in all templates, you can declare in

build.sbt

TwirlKeys.templateImports += "org.abc.backend._"

Comments

You can write server side block comments in templates using

@*
*@

:

@*********************
* This is a comment *
*********************@

You can put a comment on the first line to document your template into the Scala API doc:

@*************************************
* Home page.                        *
*                                   *
* @param msg The message to display *
*************************************@
@(msg: String)

<h1>@msg</h1>

Escaping

By default, dynamic content parts are escaped according to the template type’s (e.g. HTML or XML) rules. If you want to output a raw content fragment, wrap it in the template content type.

For example to output raw HTML:

<p>
@Html(article.content)
</p>

Next: Common
use cases

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