IdKey (Index Keyword)

Usage

To specify that the Object Identity values for this table should be formed from the property or properties on which this index is based, use the following syntax:

Index name On property_expression_list [ IdKey ];

Where:

• name is the name of the index. It is useful to follow a naming convention so that indices can be easily distinguished from properties. For example, you could include IDX at the end of all index names.

• property_expression_list is either a single property name or a comma-separated list of properties, enclosed in parentheses.

Otherwise, omit this keyword or place the word Not immediately before the keyword.

Details

This keyword specifies that the property or properties on which this index is based will be used to form the Object Identity value for this object.

The Object Identity value is used to uniquely locate persistent object instances. Once an object using IdKey has been saved, you cannot modify the values of any of the properties that make up the IdKey.

An IdKey index also behaves like a unique index. That is, for the property (or the combination of properties) that you use in this index, InterSystems IRIS enforces uniqueness. It is permitted, but redundant, to specify the Unique keyword as true in this index definition.

See Also

• Index Definitions in this book

• Define and Build Indexes in Defining a High-Performance Schema

• Introduction to Compiler Keywords in Defining and Using Classes