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Learn more about the functions ISNULL, ISUNKNOWN, IFUNKNOWN, IS A, TYPE OF, ISACTIVE, GUID.
Overview
Function | Description |
---|---|
ISNULL | Checks whether a value is unknown. |
ISUNKNOWN | Replaces a value if that value is unknown. |
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 if an instance of a specific entity type is currently active. |
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
Table of Contents | ||
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ISNULL
This function checks whether a value is unknown
Syntax
Code Block |
---|
ISNULL(expression) |
- expression - Expression that is checked.
Return type
- boolean - TRUE of the attribute is unknown, FALSE otherwise
Examples
Suppose the following data model.
...
- for Bob,
ISNULL ( Person.SequenceNumber )
= FALSE - for Jane,
ISNULL ( Person.SequenceNumber )
= TRUE
ISUNKNOWN
This function replaces a value if that value is unknown.
Syntax
Code Block |
---|
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.
...
- for Jane,
ISUNKNOWN ( Person.SequenceNumber , 999 )
= 999 - for Mary,
ISUNKNOWN ( Person.SequenceNumber , 999 )
= 667
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 |
---|
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” ) )
TYPE OF
Use this function to determine the type of an instance. The function returns the name of the entity.
Syntax
Code Block |
---|
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
.
...
Kitchen
instance the expression TYPE OF Room
= “Kitchen”...