# if Source: https://zotonic.com/docs/1849/if URI: https://zotonic.com/id/1849 Language: en Selects an argument depending on a condition. For example: ```django {{ value|if:"yes":"no" }} ``` This is a shortcut for using the tag#if tag. The same can be expressed as follows: ```django {% if value %}yes{% else %}no{% endif %} ``` Note that falsy values (0, `false`, `undefined` or empty string) evaluate to false. In templates, the compiler evaluates the condition once and only evaluates the selected argument. The other argument is not evaluated, so a model lookup in that branch does not run. Both arguments are required; use `undefined` when the false branch should produce no value. Combine the filter with `as` to reuse the selected value: ```django {% if show_image|if:m.media[id]:undefined as medium %} {{ medium.mime|escape }} {% endif %} ``` The media model is only queried when `show_image` is true. The block is rendered when the selected value is truthy, and `medium` contains that value. This lazy evaluation applies to compiled templates. Direct Erlang calls to `filter_if:'if'/4` follow normal Erlang evaluation: all arguments are evaluated before the function is called. Elaborate examples ------------------ ```django {% with is_i18n|if:r.translation[lang_code].body:r.body as body %} ``` So if `is_i18n` evaluates to true, `body` is assigned to `r.translation[lang_code].body`, else to `r.body`. ```django {% include "_language_attrs.tpl" id=pid class=(pid==id)|if:"active":"" %} ``` Add parameter `class` to the included template; when `pid` equals `id`, `class` is `"active"`, otherwise an empty string. License: Attribution: Related resources: https://zotonic.com/api/agent/related/1849?language=en ## API access - [API help]() - [OpenAPI specification]() - [This resource as JSON]()