OCLOperators Not
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"Not" is the usual Not operator found in most languages. | "Not" is the usual Not operator found in most languages. | ||
However, there are a few things to point out when writing expressions using True, False, nullable booleans, and Not. | |||
===== Avoid the | ===== Avoid the Risk With Nullable Booleans ===== | ||
Consider ''xxxx.DisableEditing = false'' | Consider ''xxxx.DisableEditing = false'' | ||
When you think you want to use "a boolean" with '''= true/false | When you think you want to use "a boolean" with '''= true/false,''' don't - it's almost never correct. | ||
The reason is that | The reason is that a nullable boolean is tri-state. '''False''', '''True,''' and '''Null'''. If an expression is xxxx.DisableEditing - that is false for BOTH False and Null. | ||
So, almost always use "xxxx.DisableEditing" or "not xxxx.DisableEditing" (there are exceptions, but not many) | So, almost always use "xxxx.DisableEditing" or "not xxxx.DisableEditing" (there are exceptions, but not many). | ||
For example | For example: | ||
self.ValidTo.notNull and | self.ValidTo.notNull and | ||
self.AddedTo.isNull and | self.AddedTo.isNull and | ||
(self.Agreement.Facilitator.DisableEditing = false) | (self.Agreement.Facilitator.DisableEditing = false) | ||
If DisableEditing is Null, then "(self.Agreement.Facilitator.DisableEditing = false)" is actually '''True'''. (the above false/null problem) | If DisableEditing is Null, then "(self.Agreement.Facilitator.DisableEditing = false)" is actually '''True'''. (the above false/null problem). | ||
self.ValidTo.notNull and | self.ValidTo.notNull and | ||
self.AddedToJournalSearch.isNull and | self.AddedToJournalSearch.isNull and | ||
not self.Agreement.Facilitator.DisableEditing | not self.Agreement.Facilitator.DisableEditing | ||
[[Category:OCLOperators]] | |||
Revision as of 07:35, 3 March 2023
"Not" is the usual Not operator found in most languages.
However, there are a few things to point out when writing expressions using True, False, nullable booleans, and Not.
Avoid the Risk With Nullable Booleans
Consider xxxx.DisableEditing = false
When you think you want to use "a boolean" with = true/false, don't - it's almost never correct.
The reason is that a nullable boolean is tri-state. False, True, and Null. If an expression is xxxx.DisableEditing - that is false for BOTH False and Null.
So, almost always use "xxxx.DisableEditing" or "not xxxx.DisableEditing" (there are exceptions, but not many).
For example:
self.ValidTo.notNull and self.AddedTo.isNull and (self.Agreement.Facilitator.DisableEditing = false)
If DisableEditing is Null, then "(self.Agreement.Facilitator.DisableEditing = false)" is actually True. (the above false/null problem).
self.ValidTo.notNull and self.AddedToJournalSearch.isNull and not self.Agreement.Facilitator.DisableEditing
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