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

Question

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

Answer 1

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__')
        -%}

See also

• SO: Similar question related to non-existent or null variables
• SO: General purpose use of default filter