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UNPACK
Extracts the value from a single valued collection or list. Is the inverse of the LIST function.
Syntax
UNPACK ( collection/list )
Input
- collection/list - A collection or list of one entity or attribute instance.
Return type
- entity instance
- attribute value of any type
Examples
Suppose the following data model.
| Person.name | Person.SequenceNumber |
|---|---|
| “Bob” | 654 |
| “Jane” | 523 |
| “Mary” | 667 |
| “Rick” | 500 |
| “Ron” | 490 |
| “Jenny” | 765 |
UNPACK ( COLLECT Person.name FROM ALL Person WHERE ( Person.SequenceNumber = MIN ( COLLECT Person.SequenceNumber FROM ALL Person ) ) )= “Ron”- In case a second entry "Ron","490" exists, the expression
UNPACK ( COLLECT Person.name FROM ALL Person WHERE ( Person.SequenceNumber = MIN ( COLLECT Person.SequenceNumber FROM ALL Person ) ) )will fail, because theUNPACKcannot resolve a list with two elements. To solve this theUNIQUEfunction has to be used:UNPACK ( UNIQUE ( COLLECT Person.name FROM ALL Person WHERE ( Person.SequenceNumber = MIN ( COLLECT Person.SequenceNumber FROM ALL Person ) ) ) )= "Ron". UNPACK ( COLLECT Person.name FROM ALL Person WHERE ( Person.SequenceNumber = MAX ( COLLECT Person.SequenceNumber FROM ALL Person ) ) )= “Jenny”
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