Module filters

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 necessary 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, State};

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

env.add_filter("append_template", append_template);

Filter configuration

The recommended pattern for filters to change their behavior is to leverage global variables in the template. For instance take a filter that performs date formatting. You might want to change the default time format format on a per-template basis without having to update every filter invocation. In this case the recommended pattern is to reserve upper case variables and look them up in the filter:

use minijinja::State;

fn timeformat(state: &State, ts: f64) -> String {
    let configured_format = state.lookup("TIME_FORMAT");
    let format = configured_format
        .as_ref()
        .and_then(|x| x.as_str())
        .unwrap_or("HH:MM:SS");
    format_unix_timestamp(ts, format)
}

env.add_filter("timeformat", timeformat);

This then later lets a user override the default either by using add_global or by passing it with the context! macro or similar.

let ctx = context! {
    TIME_FORMAT => "HH:MM",
    ..other_variables
};

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.

Some additional filters are available in the minijinja-contrib crate.

Traits

Filter

A utility trait that represents filters.

Functions

absbuiltins

Returns the absolute value of a number.

attrbuiltins

Looks up an attribute.

batchbuiltins

Batch items.

boolbuiltins

Converts the value into a boolean value.

capitalizebuiltins

Convert the string with all its characters lowercased apart from the first char which is uppercased.

defaultbuiltins

If the value is undefined it will return the passed default value, otherwise the value of the variable:

dictsortbuiltins

Dict sorting functionality.

escape

Escapes a string. By default to HTML.

firstbuiltins

Returns the first item from a list.

floatbuiltins

Converts a value into a float.

indentbuiltins

indents Value with spaces

intbuiltins

Converts a value into an integer.

itemsbuiltins

Returns a list of pairs (items) from a mapping.

joinbuiltins

Joins a sequence by a character

lastbuiltins

Returns the last item from an iterable or string.

lengthbuiltins

Returns the “length” of the value

listbuiltins

Converts the input value into a list.

lowerbuiltins

Converts a value to lowercase.

mapbuiltins

Applies a filter to a sequence of objects or looks up an attribute.

maxbuiltins

Returns the largest item from the list.

minbuiltins

Returns the smallest item from the list.

pprintbuiltins

Pretty print a variable.

rejectbuiltins

Creates a new sequence of values that don’t pass a test.

rejectattrbuiltins

Creates a new sequence of values of which an attribute does not pass a test.

replacebuiltins

Does a string replace.

reversebuiltins

Reverses an iterable or string

roundbuiltins

Round the number to a given precision.

safe

Marks a value as safe. This converts it into a string.

selectbuiltins

Creates a new sequence of values that pass a test.

selectattrbuiltins

Creates a new sequence of values of which an attribute passes a test.

slicebuiltins

Slice an iterable and return a list of lists containing those items.

sortbuiltins

Returns the sorted version of the given list.

titlebuiltins

Converts a value to title case.

tojsonbuiltins and json

Dumps a value to JSON.

trimbuiltins

Trims a value

uniquebuiltins

Returns a list of unique items from the given iterable.

upperbuiltins

Converts a value to uppercase.

urlencodebuiltins and urlencode

URL encodes a value.