= Mixins (and Mixees)

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This section defines a number of interfaces that define a contract for some framework-defined mixins.

[TIP]
====
See the xref:userguide:fun:overview.adoc#mixins[fundamentals user guide] for a discussion of mixins.
====


[#java-lang-object]
== java.lang.Object

The framework provides a number of mixins that contributes to `java.lang.Object` (in other words, to every domain object):

* core
** xref:refguide:applib:index/mixins/layout/Object_downloadLayout.adoc[Object_downloadLayout]

* Wicket viewer:
** xref:refguide:viewer:index/wicket/applib/mixins/Object_clearHints.adoc[Object_clearHints]



[[Dto]]
== Dto

JAXB view models can optionally implement the `Dto` interface.
Two mixins contribute to this interface:

* xref:refguide:applib:index/mixins/dto/Dto_downloadXml.adoc[Dto_downloadXml]
* xref:refguide:applib:index/mixins/dto/Dto_downloadXsd.adoc[Dto_downloadXsd]

These allow the view model/DTO to be seriailized, respectively, as XML and as the XSD schema for said XML.


[[Persistable]]
== Persistable


All JDO domain entities implement the DataNucleus `Persistable` role interface as a result of the enhancer process (the fully qualified class name is `org.datanucleus.enhancement.Persistable`).

Using this, the following mixins (actions and properties) are available for all JDO entities:

* xref:refguide:persistence:index/jdo/datanucleus/mixins/Persistable_datanucleusVersionLong.adoc[Persistable_datanucleusVersionLong] (property)
+
only visible if the entity is annotated with `javax.jdo.annotations.Version` and the `version` field introduced by enhancing can be cast to `Long`.

* xref:refguide:persistence:index/jdo/datanucleus/mixins/Persistable_datanucleusVersionTimestamp.adoc[Persistable_datanucleusVersionLong] (property)
+
only visible if the entity is annotated with `javax.jdo.annotations.Version` and the `version` field introduced by enhancing can be cast to `java.sql.Timestamp`.

As a developer you do not need to write any code to obtain the mixins that contribute to this interface.

These mixin properties/actions are all associated with the "Metadata" fieldset.



