Required
Usage
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.
Details
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
Opens in a new window, 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.AdaptorOpens in a new window, 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.
Notes
If a property is marked as both read-only and required, note the following difference in behavior between object access and SQL access:
When you save the object, Caché does not validate the property. This means that Caché ignores the Required keyword for that property.
When you insert or update a record, Caché does consider the Required keyword for the property.
Default
If you omit this keyword, the property is not required.
See Also
“Property Definitions” in this book
“Defining and Using Literal Properties” in Using Caché Objects
“Working with Collections” in Using Caché Objects
“Working with Streams” in Using Caché Objects
“Defining and Using Object-Valued Properties” in Using Caché Objects
“Defining and Using Relationships” in Using Caché Objects
“Introduction to Compiler Keywords” in Using Caché Objects
