A collection is a list of data. Usually you create it when retrieving attributes or relations.
You can refer to a specific element in the collection in multiple ways.
Note If a reference points to a value that doesn't exist, the rule will crash. For example, retrieving the fifth value of a list that only contains four values causes a crash.
| Reference | Result |
|---|---|
| mylist.first() | The first value in the list mylist. |
| mylist.last() | The last value from the list mylist. |
| mylist[1] | The second element from the list mylist.
The number is the index of the value you want to retrieve from the list.Note The first element has index zero. As a consequence, |
| mylist.get(1) | The second element from the list my list. It is very similar to the example above. |
| mylist?.get(1) |
The second element from the list.
However, this syntax is null-safe.
?. is the null-safe getter of Groovy. You cannot combine the ?. with the [ ... ] notation. This means that if the referenced attribute is not present, the result is null, whereas the expression without the question mark fails to execute. |