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# Configuring Mutable Mappings

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Direct mappings typically map simple, non-mutable values such as `String` or `Integer`. Transformation mappings can potentially map complex mutable object values, such as mapping several database field values to an instance of a Java class.

If a transformation mapping maps a mutable value, TopLink must clone and compare the value in a unit of work (see "Configuring Copy Policy").

By default, TopLink assumes that all transformation mappings are mutable. If the mapping maps a simple nonmutable value, you can improve unit of work performance by configuring the IsMutable option to `false`.

Table: Mapping Support for Mutable Mappings summarizes which mappings support this option.

Mapping Support for Mutable Mappings

Mapping | Using TopLink Workbench | Using Java
--- | --- | ---
Relational Mappings |  |
Transformation Mapping |  |
EIS Mappings |  |
EIS Transformation Mapping |  |
XML Mappings |  |
XML Transformation Mapping |  |