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Learn more about the functions ISNULL, ISUNKNOWN, IFUNKNOWN, IS A, TYPE OF, ISACTIVE, GUID.
Overview
Function | Description |
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ISNULL | Checks |
Table of Contents minLevel 2
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ISNULL
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whether a value is unknown |
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Syntax
Code Block |
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ISNULL(expression) |
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. |
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Return type
- boolean - TRUE of the attribute is unknown, FALSE otherwise
Examples
Suppose the following data model.
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- for Bob,
ISNULL ( Person.SequenceNumber )
= FALSE - for Jane,
ISNULL ( Person.SequenceNumber )
= TRUE
...
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Replaces a value if that value is unknown. |
Syntax
Code Block |
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ISUNKNOWN(expression, value) |
- expression- Expression of which the value has to be returned if that value is known.
- value - Value to return if the attribute value is unknown.
Return type
- any type, equals the attribute type
Examples
Suppose the following data model.
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- for Jane,
ISUNKNOWN ( Person.SequenceNumber , 999 )
= 999 - for Mary,
ISUNKNOWN ( Person.SequenceNumber , 999 )
= 667
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IS A
Use this function to check the type of an instance. The function returns TRUE if the selected instance is of the specified entity.
Syntax
Code Block |
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instance IS A entity_name |
- instance - Instance to check.
- entity_name - Name of the entity as string.
Return type
- boolean
Examples
Suppose a domain model in which there is a singleton entity Residence
that has a multivalued relation hasRooms
with Room
. Room
is the base entity for singleton Kitchen
and not singletons Bedroom
and Bathroom
.
If you want to determine the number of bedrooms is the residence:
COUNT ( COLLECT Room FROM Residence.hasRooms WHERE ( Room IS A “Bedroom” ) )
If you want to determine the number of bathrooms is the residence:
COUNT ( COLLECT Room FROM Residence.hasRooms WHERE ( Room IS A “Bathroom” ) )
IFUNKNOWN | Alternative notation of the ISUNKNOWN function, which increases readability especially for long expressions. |
IS A | Checks the entity type of an instance. |
TYPE OF | Determines the entity type of an instance. |
ISACTIVE | Determines |
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TYPE OF
Use this function to determine the type of an instance. The function returns the name of the entity.
Syntax
Code Block |
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TYPE OF base_entity |
- base_entity - Name of the instance's base entity.
Return type
- string
Examples
Suppose a domain model in which there is a singleton entity Residence
that has a multivalued relation hasRooms
with Room
. Room
is the base entity for singleton Kitchen
and not singletons Bedroom
and Bathroom
.
- for the
Kitchen
instance the expressionTYPE OF Room
= “Kitchen” - for the
Bedroom
instances the expressionTYPE OF Room = “Bedroom”
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ISACTIVE
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if an instance of a specific entity type is currently active. |
Code Block |
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ISACTIVE instances [WHERE condition] |
- instances - instances to search
- condition - optional condition to limit the collection of instances to check
Return type
boolean - TRUE if one of the instances is active, FALSE otherwise
UI Text Box type note Singletons are always active, so ISACTIVE <singleton> will always return TRUE
Examples
Suppose the following data model.
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- If no instance of Person is activated,
ISACTIVE Person
= FALSE - If
Person_1
is active,ISACTIVE Person
= TRUE - If
Person_1
is active,ISACTIVE Person WHERE Person.Age >= 18
= FALSE (sincePerson_1
is excluded by the condition) ISACTIVE system
= TRUE (system
contains the system attributes and is a singleton. Therefore it is always active)- If no instance of Person is activated, the following expression will fail because Person is not in scope:
Person.Age >= 18
ISACTIVE
function the expression can be evaluated without error:(ISACTIVE Person) AND Person.Age >= 18
UI Text Box type note Note that expression above will be evaluated from left to right, so first (ISACTIVE Person) will be evaluated (= FALSE) and therefore the result of the AND will be FALSE as well. The right hand side of the expression (Person.Name >= 18) will not be evaluated, otherwise the expression would still fail.
GUID | Generates a globally unique identifier which can later be used to uniquely mark and recognize a desired element. |
Functions
Include Page Miscellaneous function ISNULL Miscellaneous function ISNULL
Include Page Miscellaneous function ISUNKNOWN Miscellaneous function ISUNKNOWN
Include Page Miscellaneous function IFUNKNOWN Miscellaneous function IFUNKNOWN
Include Page Miscellaneous function IS A Miscellaneous function IS A
Include Page Miscellaneous function TYPE OF Miscellaneous function TYPE OF
Include Page Miscellaneous function ISACTIVE Miscellaneous function ISACTIVE
Include Page Miscellaneous function GUID Miscellaneous function GUID
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