[#javax-jdo-annotation-PrimaryKey]
= @PrimaryKey (jdo)

:Notice: Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at. http://www.apache.org/licenses/LICENSE-2.0 . Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR  CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.



The `@javax.jdo.annotation.PrimaryKey` annotation is used by JDO/DataNucleus to indicate that a property is used as the primary key for an entity with application-managed identity.

Apache Isis also uses this annotation in a very minimal way: to ensure that the framework's own logic to initialize newly instantiated objects (eg using xref:refguide:applib:index/services/factory/FactoryService.adoc[FactoryService#create(...)] does not touch the primary key, and also to ensure that the primary key property is always disabled (read-only).

[NOTE]
====
Apache Isis parses the `@NotPersistent` annotation from the Java source code; it does not query the JDO metamodel.
This means that it the `@NotPersistent` annotation must be used rather than the equivalent `<field>` link:http://www.datanucleus.org/products/accessplatform_4_0/jdo/application_identity.html[XML metadata].

Moreover, while JDO/DataNucleus will recognize annotations on either the field or the getter method, Apache Isis (currently) only inspects the getter method.
Therefore ensure that the annotation is placed there.
====

