What construct should I use to check whether a value is NULL in a Twig template?
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8 Answers
Depending on what exactly you need:
is nullchecks whether the value isnull:
{% if var is null %}
{# do something #}
{% endif %}
is definedchecks whether the variable is defined:
{% if var is not defined %}
{# do something #}
{% endif %}
Additionally the is sameas test, which does a type strict comparison of two values, might be of interest for checking values other than null (like false):
{% if var is sameas(false) %}
{# do something %}
{% endif %}
6 Comments
J.-B. C.
And to check if something is not null, simply do
{% if var is not null %}
daSn0wie
quick note that: $var == null will return true with $var is 0, but $var is null will return false
Petter Soderlund
Also note that $var == 0 will return true if $var is null
Pavel Petrov
In addition, unlike the PHP
isset() function, is defined will return true if a variable is defined and it's value is null.
ahmed hamdy
Notice: as Twig 2.x check for variable is equal to value like
is_ sameas must be {% if var is same as(false) %} not {% if var is sameas(false) %} see Doc url => twig.symfony.com/doc/2.x/tests/sameas.html |
How to set default values in twig: http://twig.sensiolabs.org/doc/filters/default.html
{{ my_var | default("my_var doesn't exist") }}
Or if you don't want it to display when null:
{{ my_var | default("") }}
2 Comments
Fluffy
So does it differentiate between
undefined or empty and null?
CTS_AE
Exactly what I was looking for. Had to make sure that you have | default which you can then try defaulting to another variable like so: {{ my_var | default(my_var2) }} I just tested, but you can even continue to chain like so: {{ my_var | default(my_var2) | default("my_var and my_var2 do not exist") }}
Without any assumptions the answer is:
{% if var is null %}
But this will be true only if var is exactly NULL, and not any other value that evaluates to false (such as zero, empty string and empty array). Besides, it will cause an error if var is not defined. A safer way would be:
{% if var is not defined or var is null %}
which can be shortened to:
{% if var|default is null %}
If you don't provide an argument to the default filter, it assumes NULL (sort of default default). So the shortest and safest way (I know) to check whether a variable is empty (null, false, empty string/array, etc):
{% if var|default is empty %}
Comments
I don't think you can. This is because if a variable is undefined (not set) in the twig template, it looks like NULL or none (in twig terms). I'm pretty sure this is to suppress bad access errors from occurring in the template.
Due to the lack of a "identity" in Twig (===) this is the best you can do
{% if var == null %}
stuff in here
{% endif %}
Which translates to:
if ((isset($context['somethingnull']) ? $context['somethingnull'] : null) == null)
{
echo "stuff in here";
}
Which if your good at your type juggling, means that things such as 0, '', FALSE, NULL, and an undefined var will also make that statement true.
My suggest is to ask for the identity to be implemented into Twig.
5 Comments
Shabbyrobe
Kendall is right to suggest that they implement it - I've had nothing but good experiences asking for things to be implemented on Twig's github issue tracker. They're very friendly and professional.
noisebleed
@kendall-hopkins Got curious, when is it appropriate to use
{if var is none} and what is the PHP equivalent?
Kendall Hopkins
@noisebleed
{% if abcxyz is none %} becomes if (isset($context["abcxyz"])) { $_abcxyz_ = $context["abcxyz"]; } else { $_abcxyz_ = null; } if ((null === $_abcxyz_)) { echo "hi"; }. So basically if the value is undefined or null, it will be true.Kendall Hopkins
Will B.
The equivalent to this answer would also be to use
{% if var is empty %} twig.sensiolabs.org/doc/tests/empty.html which translates to PHP if (empty($var)) that evaluates against a falsey value (!isset, null, 0, array(), "", false, "0", 0.0 ) php.net/manual/en/function.empty.php You can also use {% if var is same as(var) %} for identity (===). twig.sensiolabs.org/doc/tests/sameas.html //test if varibale exist
{% if var is defined %}
//todo
{% endif %}
//test if variable is not null
{% if var is not null %}
//todo
{% endif %}
3 Comments
STT LCU
Why do you think this answer is better than the currently accepted one?
Artemix
Welcome to StackOverflow! What is the difference from already accepted answer? Is it outdated? Why your answer is better than already existing ones?
crmpicco
@STTLCU He's including
if var is not null.You can also use one line to do that:
{{ yourVariable is not defined ? "Not Assigned" : "Assigned" }}
Comments
you can use the following code to check whether
{% if var is defined %}
var is variable is SET
{% endif %}
Comments
Also if your variable is an ARRAY, there are few options too:
{% if arrayVariable[0] is defined %}
#if variable is not null#
{% endif %}
OR
{% if arrayVariable|length > 0 %}
#if variable is not null#
{% endif %}
This will only works if your array is defined AND is NULL
Comments
