Templating / Building templates

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To render HTML pages with dynamic content, Bolt uses the Twig templating language. This means that everybody who is familiar with Twig can easily get started with building templates in Bolt.

In short, Twig can be described as a 'flexible, fast, and secure template engine for PHP'. Primarily, it separates the markup of your templates from the PHP code in the CMS. It does this elegantly and quickly, which means that writing your HTML templates in Twig will give you clean and legible templates.

That means you don't have to use PHP-like statements in your markup, so there's less code like this:

<?php if ( the_something('3') ) { ?>
<h1>Title is: <?php echo the_title() ?>.</h1>
<?php } ?>

Instead, more like this:

{% if something('3') %}
    <h1>Title is: {{ title }}.</h1>
{% endif %}

A template in Bolt can use all standard Twig tags, functions, filters and tests, with a few additions that are specific to working with Bolt. If you're not familiar with Twig yet, you should read "Twig for Template Designers", on the official Twig website.

Twig syntax basics¶

There are basically three different types of Twig delimiters that you can use in your templates:

• {% %} — Control structures, or "do something" actions
• {{ }} — Output structures, or "output something" action
• {# #} — Comments that are not meant for outputting to the rendered page

Inside control & output structures you can use expressions, statements, variables, functions and filters.

A simple example of these together might look like this:

{# Render the content in template.twig here #}
{% include 'template.twig' %}

{# Create a varable called "vars" containing an array #}
{% set vars = {'foo': 'bar'} %}

{# Check if the "vars" variable can be looped over #}
{% if vars is iterable %}
    {# Loop over our variable #}
    {% for key, value in vars %}
        <p>{{ key }} has the {{ value }}</p>
    {% endfor %}
{% else %}
    <p>Well this is strange!</p>
{% endif %}

For in-depth coverage you should read the Twig manual.

Control structures¶

Simply, control structures are sections of logic in your template file that "does something".

They are defined using by pairing a curly brace and a percentage sign — {% %} — that contains a "tag".

The most common tags used in a Twig template are typically:

• for that is used to iterate over an array
• if statements allow you to conditionally perform actions
• set is used to "set" a variable's value
• include statements return the rendered content of another template
• block tags are used to break out inheritable sections of templates for re-use or overriding in child templates

For example, {% if foo == "bar" %} is a statement that tests if the variable foo is equal to the value "bar". If so, the part that's between the opening statement and the corresponding {% endif %} will be rendered.

Output structures¶

As the name suggests, output structures are used to display the output of variables, or Twig functions & filters.

They are defined using by pairing two curly braces — {{ }} — that contain the instructions to give to Twig in order to output the desired text.

For example:

• {{ foo }} outputs the contents of the variable foo
• {{ bar(foo) }} outputs the results of the function bar(). In this case, 'foo' is used as an argument in the function, so the output is most likely dependent on the contents of foo.
• {{ foo|bar }} Outputs the variable foo, but with bar as a filter. If foo is "hello", {{ foo|upper }} would output "HELLO".

Comments¶

Comments are just that, to add comments to your templates, that don't do anything, but leave yourself useful information relevant to that part of the template.

They are comparable to the HTML comments like <!-- foo -->, except for the fact that Twig comments don't get sent to the browser,so you can't see them using 'view source'.

They are defined using by pairing a curly brace with a # sign — {# #} — that contain the comment's text.

For example, the following lines of a Twig template would render an empty HTML <div>, but leaves yourself a reminder to why.

<div>
    {# TODO: Add something here #}
</div>

Filesystem Layout¶

A Bolt website theme consists of a set of Twig templates, that are located in the theme folder in the public directory of your site.

You can always add more templates, if you want to. By default, the index.twig template is the homepage, but you can override it using the configuration settings.

The current default theme contains the following files and folders:

The file names of the 'helper' templates all start with an underscore. This is just a convention, to make it easier to recognize which template does what. If one of your ContentTypes have a 'template select' field, Bolt will skip these helper templates by default, when providing you with a list to select your template.

Tip: the default template set uses the include tag to insert the header, footer and such, but you're free to use Template Inheritance if you prefer.

By default, Bolt creates links to single pages based on the ContentTypes, and it uses a template based on its name.

For instance, if your site has a ContentType foos, a single record in that ContentType will be available under domain.com/foo/slug-of-record, where slug-of-record is the "slugified" version of the title. Bolt will try to use foo.twig as the template to render the page.

You can change this by either defining another template in contenttypes.yaml, or using a 'template select' field in the ContentType. More information about this can be found in the section on working with ContentTypes.

Using your themes theme.yaml you can provide overrides for certain settings of the main config.yaml. These are useful when building themes and you want to provide your own templates.

These are (provided with examples):

homepage_template: index.twig
record_template: record.twig
listing_template: listing.twig
search_results_template: listing.twig
maintenance_template: maintenance.twig

listing_template is used for both ContentType listings and taxonomy listings.

By using the template_directory setting in your themes theme.yaml you can choose the location of the templates within your theme structure.

For example to place all your templates in a directory called twig you would add the following to your theme's theme.yaml:

template_directory: twig

Template structure¶

A simple page.twig template could look something like the example you see below.

Using this example we'll go over some of the details of the Twig Template language. As mentioned before: Much, much more detailed info can be found at Twig for Template Designers on the official Twig site.

{% extends 'partials/_master.twig' %}

{% block main %}
<article>

    <h1><a href="{{ record.link }}">{{ record.title }}</a></h1>

    {# Only display the image, if there's an actual image to display #}
    {% if record.image != "" %}
        <div class='image'>
            <img src="{{ record.image|thumbnail(320, 240) }}">
        </div>
    {% endif %}

    {{ record.body }}

    <p class="meta">
        Posted by {{ record.user.displayname }} on
        {{ record.datecreated|date("M d, ’y")}}
    </p>

</article>
{% endblock main %}

What happens in this example is the following:

• {% extends 'partials/_master.twig' %}, line 1: The extends tag tells Twig that this is a child template, that inherits the content and functionality from _master.twig
• {% block main %}, line 3: The block tag, and its matching endblock on line 23, tells Twig to override the contents of the block called "main" in _master.twig
• {{ record.title }}, line 6: Since this is a generic template, record contains the record of the current requested page. For example, if the current page is domain.com/news/the-website-is-live, record would contain the record from the news ContentType that has 'the-website-is-live' as a slug. The record variable acts like an array, so to output the title field, we use dot-notation (.)
• {{ record.link }}, line 6: Here we use the link property to get the URL that links to the content
• {# Only display .. #}, line 8: This is a simple comment. It will be removed when the template is rendered to the browser, so it will not show up in 'view source'
• {% if content.image != "" %} … {% endif %}, lines 9 - 13: The if statement only parses the part between the start and end tag, if the given condition is true. So, in this case, the image is only rendered to the browser, if content.image does not equal an empty string (""), i.e. if it is not empty
• {{ record.image|thumbnail(320, 240) }}, line 11: By using the thumbnail filter, we can create thumbnail images on the fly. In this case, the image source attribute in the HTML will be something like '/thumbs/300x240/imagename.jpg'. Bolt has a built-in image resizer that will create the image with the exact dimensions, and caches it for further use.
• {{ record.body }}, line 15: This renders the body field of the ContentType record
• {{ record.datecreated|date("M d, ’y")}}, line 19: datecreated is one of the elements that is always present in all ContentTypes, and it contains the date the record was created. It's stored in a machine-readable format, so to display it the way we want, we use the date() filter. In this case, it will output something like 'August 26, ’12'.