EclipseLink : No Persistence provider for EntityManager - jpa

Question

I am trying to develop a web application. I started creating a Play! Framework project in Eclipse.
For the model part I chose to use JPA and since I had already created the database I was searching a way auto-generate the model classes.
I converted it to faceted form and used Dali to create the mapping with the database. During the configuration I was promted to chose a JPA implementation so I chose EclipseLink 2.1.3 Helios as a user library.
All the jars where added in my project.
After searching for similar errors, I modified the persistence.xml to:
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="StudentApplication">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<class>models.Grade</class>
<class>models.GradePK</class>
<class>models.Student</class>
<properties>
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/studentapplication"/>
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
<property name="javax.persistence.jdbc.user" value="root"/>
<property name="javax.persistence.jdbc.password" value="root"/>
</properties>
</persistence-unit>
</persistence>
The exact error I am getting now is:
Execution exception (In /app/controllers/class.java around line 98)
PersistenceException occured : No Persistence provider for EntityManager named jpa
I have to note that in application.conf I have declared the db connection and when I run the application I get
22:03:53,084 INFO ~ Connected to jdbc:mysql://localhost/studentapplication?useUnicode=yes&characterEncoding=UTF-8&connectionCollation=utf8_general_ci
Finally the file structure is:
-controllers
-models
-views
-META-INF
|_persistense.xml
As you may have understood (besides my rep) I am a newbie in web application development and specifically in JPA. I would be more than grateful to any kind of help. I apologize in advance if I posted not-needed information or if I missed mandatory information. Thank you for your time.
Thomas

Answer 1

It seems that you are referencing the persistence unit in your application by a different name than in your persistence.xml. Your persistence unit is named "StudentApplication" in persistence.xml. However, the error states that it is named "jpa" in your application.
Assuming that you are using application managed entity manager, there must be a line like this in your app:
EntityManagerFactory emf = Persistence.createEntityManagerFactory("jpa");
Change it to
EntityManagerFactory emf = Persistence.createEntityManagerFactory("StudentApplication");