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This is documentation for Caché & Ensemble.

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Caché & Ensemble 2018.1.3 — 2018.1.4 > Caché Development References > Caché Class Definition Reference > Property Keywords > Required
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Required

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.

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, 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.

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

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