In Twig, check if a specific key of an array exists

问题

In PHP we can check if a key exists in an array by using the function array_key_exists().

In the Twig templating language we can check if an variable or an object's property exists simply by using an if statement, like this:

{% if app.user %}
do something here
{% else %}
do something else
{% endif %}

But how do we check if a key of an array exists using Twig? I tried {% if array.key %}, but it gives me an error:

Key "key" for array with keys "0, 1, 2, 3...648" does not exist

As one of the primary ways of passing data into a template is using arrays, it seems like there should be some way of doing this. Any thoughts?

回答1:

Twig example:

{% if array.key is defined %}
  // do something
{% else %}
  // do something else
{% endif %}

回答2:

You can use the keys twig function

{% if myVar in someOtherArray|keys %}

回答3:

Quick Answer (TL;DR)

DeveloperTLindel wants to test for existence of array key in Twig.
DeveloperTLindel wants to trap any errors associated with undefined key.
This can be handled using the default filter.

Detailed Answer

Context

Twig 2.x (latest version as of Wed 2017-03-08)
General-purpose use of the default filter.

Problem

Scenario:
DeveloperTLindel wants to test for existence of array key in Twig.
DeveloperTLindel wants to avoid any errors or exceptions caused by potentially undefined key.

Solution

DeveloperTLindel can use the default filter.
The default filter catches any exceptions owing to undefined variable, and allows short-circuit substition of an alternate value.
The default filter is chainable.

Example01


{#- ****************************************
  testing for a single key in associative array
  -#} 
  {%- set mystring = myarray['key-no-existo'] |default('__BLANK__')  -%}

{#- ****************************************
  testing for a multiple keys in associative array
  -#} 
  {%- set mystring = myarray['alpha']
        |default(myarray['bravo'])
        |default(myarray['charlie'])
        |default('__BLANK__')
        -%}