Documentation:Boolean: Difference between revisions

Boolean

Latest revision as of 05:46, 20 January 2025

This page was created by Lars.olofsson@mdriven.net on 2021-09-12. Last edited by Edgar on 2025-01-20.

Definition

A boolean in OCL can be both Non-nullable and Nullable.

NonNullableBoolean : Boolean

NullableBoolean : Boolean?

As an attribute on a class that is saved to the database, almost always use non-nullable. Why? Because otherwise, it will default to null, and it's easy to handle False and Null mistakenly and incorrectly.

Evaluating

Remember to evaluate booleans like this:

class.BooleanAttribute

not class.BooleanAttribute

Not like this:

class.BooleanAttribute = True

class.BooleanAttribute = False

i.e. without an equal sign and True, False.

Mistakes We Have Seen Happen

class.BooleanAttribute->notEmpty

The expression will always return True because it will be converted to a list with one Boolean and that list will never be empty.

See also Initial values and Default Database values for more information on adding Boolean values and evolving the database

@@ Line 1: / Line 1: @@
-A boolean in OCL can be both Non-nullable and Nullable.
+<message>Write the content here to display this box</message>
+===== Definition =====
+A boolean in OCL can be both Non-nullable and Nullable.
   NonNullableBoolean : Boolean
   NullableBoolean : Boolean?
-As an attribute on a class that is saved to database, almost always use '''non-nullable'''. Why? Because otherwise it will default to null and it's easy to by mistake not handle False and Null correctly.
+As an attribute on a class that is saved to the database, almost always use '''non-nullable'''. Why? Because otherwise, it will default to null, and it's easy to handle ''False'' and ''Null'' mistakenly and incorrectly.
+===== Evaluating =====
+Remember to evaluate booleans like this:
+ '''class.BooleanAttribute'''
+ '''not class.BooleanAttribute'''
+Not like this:
+ class.BooleanAttribute = True
+ class.BooleanAttribute = False
+i.e. without an equal sign and True, False.
+===== Mistakes We Have Seen Happen =====
+ class.BooleanAttribute->notEmpty
+The expression will always return True because it will be converted to a list with one Boolean and that list will never be empty.
+See also [[Initial values and Default Database values]] for more information on adding Boolean values and evolving the database
+[[Category:OCL]]
+{{Edited|July|12|2025}}