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<h2>
<em>EMF - JPOX Integration Details</em>
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</div>
<div class="abstract">Discusses a number of specific implementation and use details of the EMF - JPOX integration.</div>
<div class="app" id="projecthome">
<ul class="minitoc">
<li>
<a href="#Requirements+on+EObjects%3A+InternalEObject">Requirements on EObjects: InternalEObject</a>
</li>
<li>
<a href="#Requirements+on+EPackages">Requirements on EPackages</a>
</li>
<li>
<a href="#Persisted+EMF+Objects+after+Commit">Persisted EMF Objects after Commit</a>
</li>
<li>
<a href="#Classloader">Classloader</a>
</li>
<li>
<a href="#Custom+Types">Custom Types</a>
</li>
<li>
<a href="#cutpaste">Move an EObject between EContainers or support cut and paste in the EMF editor</a>
</li>
<li>
<a href="#Validation">Validation</a>
</li>
<li>
<a href="#Force+a+join+table+for+1%3An+relations">Force a join table for 1:n relations</a>
</li>
<li>
<a href="#JPOX%2FRelational+Validation+and+EObject+persistency">JPOX/Relational Validation and EObject persistency</a>
</li>
<li>
<a href="#PersistenceManagerFactory+configuration">PersistenceManagerFactory configuration</a>
</li>
<li>
<a href="#Fetch+Group">Fetch Group</a>
</li>
<li>
<a href="#Direct+read+of+contained+objects%2C+container+feature+not+set">Direct read of contained objects, container feature not set</a>
</li>
<li>
<a href="#Registering+a+Persistence+Manager+Factory+Creator">Registering a Persistence Manager Factory Creator</a>
</li>
<li>
<a href="#Lazy+loading+and+proxy+objects">Lazy loading and proxy objects</a>
</li>
<li>
<a href="#Hiding+class+names%2C+using+interfaces">Hiding class names, using interfaces</a>
</li>
<li>
<a href="#notjpoxsupported">Not Supported by JPOX</a>
</li>
</ul>
<a name="N10011"></a><a name="Requirements+on+EObjects%3A+InternalEObject"></a>
<div class="h3">
<h3>Requirements on EObjects: InternalEObject</h3>
<p>The EMF JPOX persistency layer only requires that the persisted objects implement
the org.eclipse.emf.ecore.InternalEObject interface.</p>
</div>
<a name="N1001A"></a><a name="Requirements+on+EPackages"></a>
<div class="h3">
<h3>Requirements on EPackages</h3>
<p>The OR Mapper searches for the EPackage classes in the project and uses the classpath of the project of
the selected ecore file. The only requirement is that the EPackage classes (the generated interface)
extend the EMF EPackage interface directly.</p>
</div>
<a name="N10023"></a><a name="Persisted+EMF+Objects+after+Commit"></a>
<div class="h3">
<h3>Persisted EMF Objects after Commit</h3>
<p>When EMF objects have been persisted and the transaction is committed then these objects can not be
changed anymore. Only read access is possible. Please refer to the
<a class="external" href="http://www.jpox.org/docs/1_1/attach_detach.html">relevant JDO documentation</a> about this topic.</p>
</div>
<a name="N10031"></a><a name="Classloader"></a>
<div class="h3">
<h3>Classloader</h3>
<p>Teneo performs explicit classloading in specific locations. It is possible to set the classloader which is being
user by Teneo. This can be done through the org.eclipse.emf.teneo.classloader.ClassLoaderResolver class. In this class you can
register a org.eclipse.emf.teneo.classloader.ClassLoaderStrategy. The registered ClassLoaderStrategy is used by
Teneo to explicitly load classes.</p>
</div>
<a name="N1003A"></a><a name="Custom+Types"></a>
<div class="h3">
<h3>Custom Types</h3>
<p>You can register your own TypeMappings through a
call to org.jpox.TypeManager.addType. This needs to be done during initialization of the
Persistence Manager Factory. To accomplish this you need to override <a href="jpoxdatastore.html#JpoxDataStore">JPOXDataStore</a> and the
method addCustomTypes(...). Then you can register your own typemapping as follows:</p>
<pre class="code">
tm.addType(List.class.getName(), EListMapping.class.getName(),
EListWrapper.class.getName(), false, "1.4", true, false, false, clr);
</pre>
<p>See the jpox documentation <a class="external" href="http://www.jpox.org/docs/1_1/types_userdefined.html">here</a>, it is not necessary
to use the xml file to register type mappings, the call to the TypeManager above will also work.</p>
</div>
<a name="N10053"></a><a name="cutpaste"></a>
<div class="h3">
<h3>Move an EObject between EContainers or support cut and paste in the EMF editor</h3>
<p>In the standard approach it is not possible to move an EObject from one containment relation to another containment relation. A move
between containment relations corresponds to a cut and paste in the EMF editor. The reason is that Teneo will
specify an dependent-element="true" for a containment relation. This has as a consequence that JPOX will throw
an exception (Cannot write fields to a deleted object) when you move an EObject from its container to another container.</p>
<p>
<em>Solution:</em> as a solution you can prevent the dependent-element from being set, by specifying
an annotation on the relevant EReference features. As an example:</p>
<pre class="code">
<xsd:element maxOccurs="unbounded" minOccurs="0" name="books" type="lib:Book">
<xsd:annotation>
<xsd:appinfo source="teneo.jpa">@OneToMany(cascade={MERGE,PERSIST,REFRESH,REMOVE})</xsd:appinfo>
</xsd:annotation>
</xsd:element>
</pre>
<p>This annotation means that cascading deletes are still enforced but a child (the Writer) can exist without its
parent (the Library).</p>
<p>When this annotation is used in the context of a JPOX Resource then when an EObject is removed from
its container then it will also be removed from the resource and from the database. However, when you set this
annotation and not work with JPOX Resources then the removed EObject is not removed from the database and will
be present without a container!</p>
</div>
<a name="N1006C"></a><a name="Validation"></a>
<div class="h3">
<h3>Validation</h3>
<p>When storing and retrieving EMF objects from a JPOX store it is not required to work with a
EMF type Resource. However the standard EMF validator checks if every EObject is
present in an EMF resource and that all referenced EObjects are in the same resource. So, if
this standard validator is used unnecessary errors are thrown.
</p>
<p>To prevent this situation you can register your own validator which does not perform this resource check.
For your convenience it is also possible to use the org.eclipse.emf.teneo.jpox.validation.JPOXValidator. See its
source code below.
</p>
<p>
Validators are registered using a call to put method of the EValidator.Registry.INSTANCE object.
</p>
<pre class="code">
public class JPOXValidator extends EObjectValidator
{
/**
* Overrides the method from the superclass to prevent this check because it
* is not required in the context of a jdo store. Note that this assumes that
* an object and its references are all stored in the same jpox database.
*/
public boolean validate_EveryReferenceIsContained(EObject eObject, DiagnosticChain diagnostics,
Map context)
{
return true;
}
}
</pre>
</div>
<a name="N10080"></a><a name="Force+a+join+table+for+1%3An+relations"></a>
<div class="h3">
<h3>Force a join table for 1:n relations</h3>
<p>In a relational database 1:n relations are often modeled by adding a foreign-key (to the
parent) in the child table/object. The disadvantage of this approach is that duplicates
are not supported. To support duplicates in an elist a join table is required. To signal to
Teneo, that a join table should be used, the annotation as in this example can be used:</p>
<pre class="code">
<xsd:element name="joinedItem" type="xsd:anyURI" ecore:reference="this:Item" maxOccurs="unbounded">
<xsd:annotation>
<xsd:appinfo source="teneo.jpa">@OneToMany(unique=false)</xsd:appinfo>
</xsd:annotation>
</xsd:element>
</pre>
<p>Based on this annotations Teneo will generate a join table for this model. Note that
this annotation can be combined with the indexed annotation.</p>
<p>
<em>The unique annotation does not exist in the EJB3 spec and is a Teneo extension.</em>
</p>
</div>
<a name="N10094"></a><a name="JPOX%2FRelational+Validation+and+EObject+persistency"></a>
<div class="h3">
<h3>JPOX/Relational Validation and EObject persistency</h3>
<p>When an object is made persistent using JPOX then it is almost always directly written to the backing
relational store. At that moment also constraints, such as nullable fields, are checked. This means that
only valid EObjects should be made persistent using the PersistenceManager makePersistent call.</p>
<p>
<em>An object is also made persistent when it is added to the collection of a persistent object.
So only valid objects should be added to the collection of a persistent object</em>. See the example below.</p>
<p>The following source will result in an error because the Book object does not have its title set when
it is added to the library.</p>
<pre class="code">
Book book = LibraryFactory.eINSTANCE.createBook();
lib.getBooks().add(book); // ERROR, here the book does not have a title yet!
book.setAuthor(writer);
book.setPages(305);
book.setTitle("The Hobbit");
book.setCategory(BookCategory.SCIENCE_FICTION_LITERAL);
</pre>
<p>To make this valid, the book should be added to the library after all its values have been set.</p>
</div>
<a name="N100AD"></a><a name="PersistenceManagerFactory+configuration"></a>
<div class="h3">
<h3>PersistenceManagerFactory configuration</h3>
<p>PersistenceManagerFactories should be created through a call to the relevant methods in the JPOXHelper.INSTANCE
object. If only the database connection information is passed then the JPOXHelper will
use the configuration properties below. for
more information see the jpox site <a class="external" href="http://www.jpox.org/docs/1_1/pmf.html">here</a>.</p>
<pre class="code">
properties.setProperty(PMFConfiguration.JDO_IGNORECACHE_PROPERTY, "false");
properties.setProperty(PMFConfiguration.JDO_RETAINVALUES_PROPERTY, "true");
properties.setProperty(PMFConfiguration.JDO_NONTRANSACTIONAL_READ_PROPERTY, "true");
properties.setProperty(PMFConfiguration.STRING_DEFAULT_LENGTH_PROPERTY, "255");
properties.setProperty("javax.jdo.PersistenceManagerFactoryClass", "org.jpox.PersistenceManagerFactoryImpl");
// set it all to false because of performance
properties.setProperty(PMFConfiguration.AUTO_CREATE_SCHEMA_PROPERTY, "false");
properties.setProperty(PMFConfiguration.AUTO_CREATE_CONSTRAINTS_PROPERTY, "false");
properties.setProperty(PMFConfiguration.AUTO_CREATE_SCHEMA_PROPERTY, "false");
properties.setProperty(PMFConfiguration.AUTO_CREATE_TABLES_PROPERTY, "false");
properties.setProperty(PMFConfiguration.VALIDATE_COLUMNS_PROPERTY, "false");
properties.setProperty(PMFConfiguration.VALIDATE_CONSTRAINTS_PROPERTY, "false");
properties.setProperty(PMFConfiguration.VALIDATE_TABLES_PROPERTY, "false");
properties.setProperty(PMFConfiguration.CACHE_LEVEL_1_TYPE_PROPERTY,
"org.eclipse.emf.teneo.jpox.cache.EMFWeakRefCache");
properties.setProperty(PMFConfiguration.METADATA_JDO_FILE_EXTENSION_PROPERTY,
JpoxHelper.INSTANCE.getJdoFileExtension());
</pre>
<p>
<em>For the EMF - JPOX integration it is very important that as a level1 cache one of the
cache implementations found in org.eclipse.emf.teneo.jpo.xemf.cache is used.</em>
</p>
<p>The default String length is set to prevent a bug in MySql, the JDO default is 256.</p>
<p>The AUTO_CREATE_* and VALIDATE_* properties are set this way for performance reasons. At initialization time the JpoxDataStore will override these properties to update the database schema,
see also here <a href="jpoxdatastore.html#options">options</a>.</p>
<p>You can set the file extension to use through the JpoxHelper.INSTANCE.setJdoFileExtension, this allows you to
more easily test multiple package.jdo files.</p>
<p>The current integration will not work properly if one of the following settings is used:</p>
<ul>
<li>org.jpox.delayDatastoreOperationsUntilCommit to true does not work with bi-directional references</li>
<li>javax.jdo.option.Optimistic set to true does not work with bi-directional references.
The current EMF/JPOX integration works with pessimistic transactions. However, in the current
JPOX version records are not locked in the database (<a class="external" href="http://www.jpox.org/docs/1_1/transactions.html">see</a>).</li>
</ul>
</div>
<a name="N100E0"></a><a name="Fetch+Group"></a>
<div class="h3">
<h3>Fetch Group</h3>
<p>A FetchGroup defines which fields are read when an object is loaded from the data store. The EMF - JPOX
integration sometimes overrides the working of a FetchGroup because containment references are always
read.</p>
</div>
<a name="N100EA"></a><a name="Direct+read+of+contained+objects%2C+container+feature+not+set"></a>
<div class="h3">
<h3>Direct read of contained objects, container feature not set</h3>
<p>When an object is contained and is read directly (using a JDO query) then its container feature is not set.
For example, a Book is contained in the Library (see tutorial). If a jdo query reads all books then these books
EMF objects do not have their container set. If a library object is read which contains books then
the books will have their container feature set.</p>
<p>Since the 0.6.3 release the container can be set explicitly after retrieving the
contained EObjects directly from the database, see <a href="jpoxdatastore.html#setcontainer">here</a>.
</p>
</div>
<a name="N100FB"></a><a name="Registering+a+Persistence+Manager+Factory+Creator"></a>
<div class="h3">
<h3>Registering a Persistence Manager Factory Creator</h3>
<p>You can register your own persistence manager factory creator class. This
class is called by Teneo to create a PersistenceManagerFactory. By registering your
own PersistenceManagerFactoryCreator, you can override the creation of persistence managers etc.</p>
<p>The persistence manager factory creator should implement the interface:
org.eclipse.emf.teneo.jpox.PMFCreator. The creator can be registered using
the method JpoxHelper.INSTANCE.setPMFCreator(....).</p>
</div>
<a name="N10107"></a><a name="Lazy+loading+and+proxy+objects"></a>
<div class="h3">
<h3>Lazy loading and proxy objects</h3>
<p>As a default when an object is loaded from the JPOX store only the primitive type fields are read
immediately. Reference fields and collections are lazely loaded, only when required. This behavior is
very similar to the proxy object behavior of standard EMF resource implementations.</p>
<p>If even 'more lazy' behavior is required then it is possible to set the fetch group on the
PersistenceManager, <a class="external" href="http://www.jpox.org/docs/1_1/fetchgroup.html">see</a>
</p>
</div>
<a name="N10117"></a><a name="Hiding+class+names%2C+using+interfaces"></a>
<div class="h3">
<h3>Hiding class names, using interfaces</h3>
<p>EMF is very interface oriented and tries to hide the generated implementation classes. JPOX
on the other hand requires the use of the implementation classes in queries. The runtime layer
supports the conversion of an EMF interface name to a implementation class through the JpoxHelper.INSTANCE.getInstanceClass method.
With this it is possible
to work with EMF interfaces without using the implementation class names directly.</p>
</div>
<a name="N10121"></a><a name="notjpoxsupported"></a>
<div class="h3">
<h3>Not Supported by JPOX</h3>
<p>Lists of user-defined primitive types are not supported, an example is a list
of enumerates</p>
</div>
</div>
</div>
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