Caché Class Definition Reference
[Home] [Back] [Next]
InterSystems: The power behind what matters   

For a persistent class, specifies that the property’s value must be given a value before it can be stored to disk. For an XML-enabled class, specifies that the element to which the property is mapped is required.
To specify that the property is required, use the following syntax:
Property name As classname [ Required ];
Otherwise, omit this keyword or place the word Not immediately before the keyword.
For a persistent class, this keyword specifies that the property must be given a value before the containing object can be stored to disk; an error occurs if the property does not have a value. If a property is of type %Stream, the stream cannot be a null stream. That is, the property is considered to have a value if the %IsNull() method returns 0.
For a class that extends %XML.Adaptor, this keyword affects the corresponding XML schema. If a property is marked Required, then the corresponding element in the schema does not have minOccurs="0" and is thus considered required. See Projecting Objects to XML. Note that in this case, the class does not have to be a persistent class. XML schema validation occurs when Caché reads an XML document; see Using Caché XML Tools.
In a subclass, you can mark an optional property as required, but you cannot do the reverse.
If a property is marked as both read-only and required, note the following difference in behavior between object access and SQL access:
If you omit this keyword, the property is not required.
See Also

Send us comments on this page
Copyright © 1997-2019 InterSystems Corporation, Cambridge, MA