How to check if a variable or value exists using Twig
Expected results for conditional tests using is defined, length, is not empty, is not null
Below is a reference for the expected results for numerous conditional tests you can perform in your Twig templates. For a broader discussion and examples on how and when to use these conditional tests, see Testing if something exists: is defined, length, is not null, is not empty
| devMode | is defined | variable | length | is not empty | is not null | |
|---|---|---|---|---|---|---|
| nonExistentVariable | true | False |
Template Error: Variables does not exist
|
|||
| nonExistentVariable | false | False | False | False | False | False |
| nonExistentVariable.attribute | true | False |
Template Error: Variable does not exist
|
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| nonExistentVariable.attribute | false | False | False | False | False | False |
| nonExistentVariable['attribute'] | true | False |
Template Error: Impossible to access a key
("nonExistentAttribute") on a null variable
|
|||
| nonExistentVariable['attribute'] | false | False | False | False | False | False |
| string | true/false | True | True | True | True | True |
| string (empty) | true/false | True | False | False | False | True |
| 0 | true/false | True | False | True | True | True |
| 1 | true/false | True | True | True | True | True |
| true | true/false | True | True | True | True | True |
| false | true/false | True | False | False | False | True |
| null | true/false | True | False | False | False | False |
Associative and multi-dimensional arrays (Hashes)
Twig refers to associative arrays and multi-dimensional arrays as hashes (an abbreviation for hash table).
| devMode | is defined | variable | length | is not empty | is not null | |
|---|---|---|---|---|---|---|
| array | true/false | True | True | True | True | True |
| array (empty) | true/false | True | False | False | False | True |
| array.attribute | true/false | True | True | True | True | True |
| array.nonExistentAttribute | true | False |
Template Error: Key does not exist as the array
is empty
|
|||
| array.nonExistentAttribute | false | False | False | False | False | False |
| array['attribute'] | true/false | True | True | True | True | True |
| array['nonExistentAttribute'] | true | False |
Template Error: Key "nonExistentAttribute" for
array with keys "keyName1, keyName2" does not exist
|
|||
| array['nonExistentAttribute'] | false | False | False | False | False | False |
| attribute(array, 'attribute') | true/false | True | True | True | True | True |
| attribute(array, 'nonExistentAttribute') | true | False |
Template Error: Key "nonExistentAttribute" for
array with keys "keyName1, keyName2" does not exist
|
|||
| attribute(array, 'nonExistentAttribute') | false | False | False | False | False | False |
Objects
The results below use the EntryModel as an example. In Craft 2, the
only reliable way to test for an attribute of your object (such as a
custom field), is to use array syntax:
object['attribute'].
| devMode | is defined | variable | length | is not empty | is not null | |
|---|---|---|---|---|---|---|
| object | true/false | True | True | True | True | True |
| object.attribute | true/false | True | True | True | True | True |
| object.nonExistentAttribute | true | True |
CException: Craft\EntryModel and its behaviors do
not have a method or closure named "nonExistentAttribute".
|
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| object.nonExistentAttribute | false | True |
Internal Server Error: Craft\EntryModel and its
behaviors do not have a method or closure named
"nonExistentAttribute".
|
|||
| object['attribute'] | true/false | True | True | True | True | True |
| object['nonExistentAttribute'] | true | False |
Template Error: Key "nonExistentAttribute" in
object with ArrayAccess of class "Craft\EntryModel" does not
exist
|
|||
| object['nonExistentAttribute'] | false | False | False | False | False | False |
| attribute(object, 'attribute') | true/false | True | True | True | True | True |
| attribute(object, 'nonExistentAttribute') | true | True |
CException: Craft\EntryModel and its behaviors do
not have a method or closure named "nonExistentAttribute".
|
|||
| attribute(object, 'nonExistentAttribute') | false | True |
Internal Server Error: Craft\EntryModel and its
behaviors do not have a method or closure named
"nonExistentAttribute".
|
|||
Notes
- True: Test returns True.
- False: Test returns False.
- True: Test only returns True. False results are wrong or throw errors.
- True: Test will incorrectly return True in some cases when results should be False.
Conditionals: All true results in the table above indicate that your variable exists or has a value. The default empty and null were updated to test for a value using not empty and not null so they can be easily compared to the results testing for a variable alone or using the length filter.
Objects: Objects and arrays in Twig can typically be accessed and tested in the same way, however, currently, the most reliable way to access your object attributes is using array syntax: object['attribute']. This is due to how PHP allows objects to be defined using magic methods and how Twig tests for the existence of variables and methods on those objects. In Craft 2, when an object uses the magic __call() method, Twig gets confused and always returns true.
Optimization: No testing has been done to determine which of the above tests may be the most performant. In some cases, using the length or is not empty tests may add an additional query to your page load. Testing directly for the variable or using is not null appears to not add any additional queries to your page load.