Documentation:OCLOperators notNull

OCLOperators notNull

This page was created by Hans.karlsen on 2017-11-20. Last edited by Wikiadmin on 2026-07-29.

You use notNull in OCL to test whether a value is present; it is for anyone writing an expression, constraint, or action that must handle missing attribute or variable values.

Syntax

value.notNull

notNull returns a Boolean value:

Expression result	`notNull` returns
The value has a value	`true`
The value is null	`false`

Check an attribute

Given a Car class with a Name attribute, use notNull to test whether Name has been assigned a value:

self.Name.notNull

The expression returns true when Name has a value. It returns false when Name is null.

For example, use the test before an expression that depends on Name being present:

if self.Name.notNull then
  self.Name
else
  'No name assigned'
endif

Check a variable

You can also test a variable before using it:

vCar.notNull

This returns true when vCar refers to a value and false when it is null.

Use notNull for comparison, not nullValue

Use notNull when you need to determine whether a value is null. Do not compare a value directly to <Type>.nullValue.

vCar.notNull

Use nullValue when you need a typed null value for an assignment or to return null from a method. For example, it can unset an attribute; it is not the null-comparison mechanism.

notNull and notEmpty are different

notNull checks whether one value is null. It does not test whether a collection contains items.

Use notEmpty only when you need to determine whether a collection has at least one element. Do not use ->notEmpty on a value type: the value is converted to a one-item list, causing the test to evaluate to true.

Inverse operator

isNull is the inverse of notNull:

Value state	`value.notNull`	`value.isNull`
Value is present	`true`	`false`
Value is null	`false`	`true`

Contents