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 %StreamOpens in a new tab, 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 tab, 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:
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When you save the object, Caché does not validate the property. This means that Caché ignores the Required keyword for that property.
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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
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“Property Definitions” in this book
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“Defining and Using Literal Properties” in Using Caché Objects
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“Working with Collections” in Using Caché Objects
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“Working with Streams” in Using Caché Objects
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“Defining and Using Object-Valued Properties” in Using Caché Objects
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“Defining and Using Relationships” in Using Caché Objects
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“Introduction to Compiler Keywords” in Using Caché Objects
