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Learn more about the collection functions EXISTS, EACH, ALL, COLLECT FROM WHERE, COLLECT FROM NAMED WHERE, COLLECT, UNPACK, LIST, SIZE, UNIQUE, SUBSET OF, UNION, INTERSECTION, DIFFERENCE, SYMMETRIC_DIFFERENCE. 

Overview

FunctionDescription
EXISTSDetermines

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EXISTS

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whether an instance of a specified entity exists, optionally meeting certain criteria

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Syntax

Code Block
EXISTS instances [ WHERE ( condition ) ]
  • instances - Instances to search.
  • condition - boolean expression that represents the criterion the instance has to meet.

Return type

  • boolean

Examples

Suppose the following data model.

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EACH

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Determines whether all instances of a specified entity meet a certain criteria

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Syntax

Code Block
EACH instances WHERE ( condition )
  • instances - A collection of instances to search.
  • condition - Boolean expression that represents the criterion the instance has to meet.

Return type

  • boolean

Examples

Suppose the following data model.

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ALLCreates

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ALL

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a collection of all instances of a specified

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Syntax

Code Block
 ALL entity
  • entity - Entity of which to collect all its instances.

Return type

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entity

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Examples

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COLLECT FROM [WHERE]

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Creates a collection of entity or attribute instances (meeting certain criteria).

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Code Block
 COLLECT entity | attribute FROM collection [ WHERE ( expression ) ]
  • entity or attribute - Entity or attribute to collect.
  • collection - A collection of entity instances.
  • expression - Boolean expression that represents the criterion the instance has to meet.

Return type

  • collection of entity instances
  • collection of attribute values
COLLECT

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Examples

Suppose the following model. Entity Teacher has a multivalued relation with entity Child via the relation Teacher.teaches_Children.

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COLLECT Child.name FROM ALL Child
WHERE ( Child.hobbies = "Reading" )

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FROM

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NAMED [WHERE]

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Version of

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COLLECT FROM [WHERE]

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for complex nested selections

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Syntax

Code Block
 COLLECT entity | attribute FROM collection NAMED alias [ WHERE ( expression ) ]
  • entity or attribute - Entity or attribute to collect. This should contain the alias, e.g. alias.Name.
  • collection - A collection of entity instances.
  • alias - A name for the collection.
  • expression - Boolean expression that represents the criterion the instance has to meet.

Return type

  • collection of entity instances
  • collection of attribute values
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A collections contains no duplicates. Intermediary COLLECT expressions can contain duplicates however, please see the note on collections and duplicates.

Examples

Suppose the following model with only instances of entity Person. Person.hasChildren is a relation from Person to Person.

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To retrieve all the parent names, we use this expression:

Code Block
COLLECT Parent.name 
FROM
  COLLECT Person 
  FROM ALL Person 
  WHERE ( Person.hasChildren != ? ) NAMED Parent

This expression results in “Rick”, “Julia” and “Joan”.

To retrieve all children names, we use this expression:

Code Block
COLLECT Child
FROM (
  COLLECT Person.hasChildren 
  FROM ALL Person 
  WHERE ( Person.hasChildren != ? ) ) NAMED Child

This expression results in a collection of three instances of Person (i.e Person_1, Person_3 and Person_5, with names Kim, Bob and Sam).

To retrieve all children younger than 15, we use this expression:

Code Block
COLLECT Child 
FROM (
  COLLECT Person.hasChildren
  FROM ALL Person 
  WHERE ( Person.hasChildren != ? ) ) NAMED Child
WHERE ( Child.Age < 15 )

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with

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To retrieve the children’s names with a parent older than 40 years:

Code Block
COLLECT Child.Name 
FROM (
  COLLECT Person.hasChildren 
  FROM ALL Person 
  WHERE ( Person.hasChildren != ? AND Person.Age > 40 ) ) NAMED Child

This expression results in a collection with only the name “Kim”.

You can make it as complex as you like, for example:

Code Block
COLLECT Child.Name 
FROM (
  COLLECT Parent.hasChildren
  FROM (
    COLLECT Person
    FROM ALL Person 
    WHERE ( Person.hasChildren != ? ) ) NAMED Parent
  WHERE ( Parent.Age > 40 )
) NAMED Child 
WHERE ( Child.Age < 18 )

This expression results also in a collection with only the name “Kim”.

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an alias

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Code Block
thisPerson := Person ;
 
COLLECT Person
    FROM ALL Person 
    WHERE ( Person != thisPerson )

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UNPACK

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UNPACKExtracts the value from a single valued collection or list.

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Is the inverse of the LIST function.

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Code Block
UNPACK ( collection/list )
  • 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.

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  • 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 the UNPACK cannot resolve a list with two elements. To solve this the UNIQUE function 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”

LISTCreates

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LIST

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a list based on a value.

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Is the inverse of the UNPACK function

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Syntax

Code Block
LIST ( attribute/collection )

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This function determines the size of a collection.

Syntax

Code Block
SIZE ( collection )
  • collection - A collection of attribute or entity instances. This can be an expression or a relation attribute for instance.

Return type

  • integer

Example

Suppose you have a Parent and a Child entity, where Parent has a multivalued relation with Child via the relation Parent.has_Children. With this model the following instances are created:

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Then:

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SIZE and COUNT are similar except for ?:

SIZE ( ? ) results in 0, while COUNT ( ? ) results in ?

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UNIQUE

The UNIQUE function filters duplicate items from a collection. An expression resulting in a collection, never contains duplicate values. A subexpression with the COLLECT statement however, can contain duplicates. See the note on collections and duplicates for more info.

Syntax

Code Block
 UNIQUE ( collection )
  • collection - A collection of attribute or entity instances.

Examples

Suppose the following model.

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Return type

  • a multivalued list with entries of any type

Examples

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Suppose the following data model.

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  • LIST ( COLLECT Person.name FROM ALL Person ) = [ "Bob" , "Jane" , "Mary" , "Rick" , "Ron" , "Jenny" ]
    • In this example the LIST function adds no value, as the result of the COLLECT is already a list.
  • LIST ( COLLECT Person.SequenceNumber FROM ALL Person ) = []
    • As Jenny has an unknown sequence number, the result of the COLLECT expression is ?. The LIST function creates an empty list in case the parameter has ? value.
SIZEDetermines the size of a collection.
UNIQUEFilters duplicate items from a collection resulting from a subexpression in a larger expression.
SUBSET OFReturns
TRUE if the items in a collection are all present in another collection.

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Syntax

Code Block
 collection1 SUBSET OF collection2
  • collection1 - The collection that is tested to be a subset of the second collection.
  • collection2 - The collection that is tested to hold all the items in the first collection.

Return type

  • boolean

Diagram

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Examples

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Values between single quotes are considered value list items. For backwards compatibility reasons, a comma separated sequence of value list items is treated as a collection. That's why there is no need to enclose the values between square brackets. In fact if you do add the square brackets you create a matrix rather than a list.

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UNIONAdds two collections of the same base type to a

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Syntax

Code Block
 UNION ( collection1 , collection2 )

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collection1 - First collection to be added to the new collection.

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new collection.

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Return type

  • collection

Diagram

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Examples

Suppose you have a Parent and a Child entity, where Parent has a multivalued relation with Child via the relation Parent.has_Children. With this model the following instances are created:

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INTERSECTIONDetermines

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INTERSECTION

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the intersection of two collections.

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Syntax

Code Block
INTERSECTION ( collection1 , collection2 )

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Return type

  • collection

Diagram

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Examples

Suppose the following model. Entity Teacher has a multivalued relation with entity Child via the relation Teacher.teaches_Children.

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DIFFERENCEDetermines the difference between 2 collections. Returns

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DIFFERENCE

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a collection containing all the items from collection1 that are not present in collection2.

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Syntax

Code Block
DIFFERENCE ( collection1 , collection2 )

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Return type

  • collection

Diagram

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Examples

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SYMMETRIC DIFFERENCE

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SYMMETRIC_DIFFERENCEDetermines the symmetric difference between two collections.

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 Returns a collection with the elements of the provided collections which are in either one of the collections, but not in both.

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Syntax

Code Block
SYMMETRIC_DIFFERENCE ( collection1 , collection2 )

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Return type

  • collection

Diagram

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Examples

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A note on collections and duplicates

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An expression resulting in a collection does not contain duplicates. Please be aware however, that intermediary results of a COLLECT statement can contain duplicates. You have to be aware of this when using the SIZE or UNPACK function.

This is best illustrated with the following examples.

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Now an example with the UNPACK function. We leave out the first instance from the previous example.

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Functions

Include Page
Collection function EXISTS
Collection function EXISTS


Include Page
Collection function EACH
Collection function EACH


Include Page
Collection function ALL
Collection function ALL


Include Page
Collection function COLLECT FROM WHERE
Collection function COLLECT FROM WHERE


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Collection function COLLECT FROM NAMED WHERE
Collection function COLLECT FROM NAMED WHERE


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Collection function UNPACK
Collection function UNPACK


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Collection function LIST
Collection function LIST


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Collection function SIZE
Collection function SIZE


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Collection function UNIQUE
Collection function UNIQUE


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Collection function SUBSET OF
Collection function SUBSET OF


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Collection function UNION
Collection function UNION


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Collection function INTERSECTION
Collection function INTERSECTION


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Collection function DIFFERENCE
Collection function DIFFERENCE


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Collection function SYMMETRIC_DIFFERENCE
Collection function SYMMETRIC_DIFFERENCE


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A note on collections and duplicates
A note on collections and duplicates

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 Only the intermediary results of a COLLECT statement can contain duplicates. The functions UNIQUE, UNION, INTERSECTION, DIFFERENCE and SYMMETRIC_DIFFERENCE always return collections without duplicates.

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