Module minijinja::filters

Expand description

Filter functions and abstractions.

MiniJinja inherits from Jinja2 the concept of filter functions. These are functions which are applied to values to modify them. For example the expression {{ 42|filter(23) }} invokes the filter filter with the arguments 42 and 23.

MiniJinja comes with some built-in filters that are listed below. To create a custom filter write a function that takes at least a value, then registers it with add_filter.

Using Filters

Using filters in templates is possible in all places an expression is permitted. This means they are not just used for printing but also are useful for iteration or similar situations.

Motivating example:

<dl>
{% for key, value in config|items %}
  <dt>{{ key }}
  <dd><pre>{{ value|tojson }}</pre>
{% endfor %}
</dl>

Custom Filters

A custom filter is just a simple function which accepts its inputs as parameters and then returns a new value. For instance the following shows a filter which takes an input value and replaces whitespace with dashes and converts it to lowercase:

fn slugify(value: String) -> String {
    value.to_lowercase().split_whitespace().collect::<Vec<_>>().join("-")
}

env.add_filter("slugify", slugify);

MiniJinja will perform the necessary conversions automatically. For more information see the Filter trait.

Accessing State

In some cases it can be necesary to access the execution State. Since a borrowed state implements ArgType it’s possible to add a parameter that holds the state. For instance the following filter appends the current template name to the string:

use minijinja::value::Value;
use minijinja::State;

fn append_template(state: &State, value: &Value) -> String {
    format!("{}-{}", value, state.name())
}

env.add_filter("appendTemplate", append_template);

Built-in Filters

When the builtins feature is enabled a range of built-in filters are automatically added to the environment. These are also all provided in this module. Note though that these functions are not to be called from Rust code as their exact interface (arguments and return types) might change from one MiniJinja version to another.