SCA Java implementation.jpa (TUSCANY) created by Luciano Resende
http://cwiki.apache.org/confluence/display/TUSCANY/SCA+Java+implementation.jpa
Content:
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h1.Injection of JPA Entity Manager Factory/Entity Manager
The injection of JPA Entity Manager Factory/Entity Manager would allow sharing
of EMFs across multiple components, this would be useful in scenarios where you
have conversation. In this case, the runtime would be responsible for making
sure the EM would be created and closed transparently for the application
developer based on the conversation.
h1. JPA Data Services
In this case, we would be extending the SCA programming model to expose
services that interact with a persistent layer in a declarative fashion hiding
the implementation details from the service developer.It's all about
simplicity, allowing a service to be defined without explicitly coding the
persistence layer. This would be a new Tuscany Component Type named
Implementaiton.JPA. A developer would provide the business objects that would
by JPA to do the OR mapping, and a business interface that would be introspect
by Tuscany to properly make the JPA calls to the persistence layer to retrieve
the information. Information on how to connect to the data source would be done
in the composite, and we could provide some annotations to read
h4. Business Object
The business object can be defined as per JPA programming model. You can
define it as a JPA Entity and make use of JPA annotations, or use the ORM.xml
as well.
{code}
@Entity
public class Customer {
@Id protected int id;
@Basic protected String name;
@Basic protected String phone;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
}
{code}
h4. Business Interface
The Business interface would define the access to the JPA entities, and we
would introduce Java Annotations to bind a specific method to a JPA query.
{code}
import org.osoa.sca.annotations.Remotable;
@Remotable
public interface CustomerService {
Customer[] getCustomers();
void setCustomer(Customer customer);
@Query(SELECT c FROM customer c WHERE c.name = '" + name + "'")
Customer queryCustomerByName(String name);
}
{code}
We would use some Convention over Configuration to bind the interfaces methods
to proper database activities :
| Method | Correspondent db operation |
| createXXX | Insert a new entity on the db. A collection of new entities
should also be supported |
| getXXX | Read a given entity from the db \\ A method signature with no
parameters read a collection. |
| setXXX | Update a previously existent entity on the db. |
| deleteXXX | Remove a previously existent entity on the db. |
| queryXXX | Execute a query on the db. \\ We would introduce a Java
Annotation to bind a given query to the method invocation |
Note that introspection will be required by the runtime to properly identify
the operation type being requested. Based on this introspection, the runtime
will also be responsible for any necessary conversion to the proper collection
being expected as a result.
h4. Composite
{code}
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0";
xmlns:tuscany="http://tuscany.apache.org/xmlns/sca/1.0";
targetNamespace="http://sample/implementation.jpa";
name="customer">
<component name="CustomerServiceComponent">
<tuscany:implementation.jpa>
<tuscany:persistence-unit name="customer">
<tuscany:class>assets.Customer</tuscany:class>
</tuscany:persistence-unit>
<tuscany:connectionInfo>
<tuscany:connectionProperties
driverClass="org.apache.derby.jdbc.EmbeddedDriver"
databaseURL="jdbc:derby:target/test-classes/customer; create = true"
loginTimeout="600000"/>
</tuscany:connectionInfo>
</tuscany:implementation.jpa>
</component>
</composite>
{code}
h1. Benefits
* Simplify the programming model for accessing data, hiding some of the API
details required for this kind of components
* Allow exposing data services trough multiple SCA Bindings (e.g ws, json-rpc,
feeds, etc)
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