JPA Tutorial With EclipseLink explains step by step details of setting / configuring Java Persistence(JPA) With Hibernate And Eclipse. By focusing first on JPA, the EclipseLink project enables broad .. Read more about JPA at JPA Tutorial – Java Persistence API (you will learn. EclipseLink tutorial covers the basics of EclipseLink, the official implementation of the Java Persistence API.
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Via JPA the developer can map, store, update and retrieve data from relational databases to Java objects and vice versa. JPA is a specification and several implementations are available. The JPA implementation is typically called persistence provider.
The mapping between Eclipselunk objects and database tables is defined via persistence metadata. The JPA provider will use the persistence metadata information to perform the correct database operations.
JPA metadata is typically defined via annotations in the Java class. Alternatively, the metadata can be defined via XML or a combination of both. A XML configuration overwrites the annotations. Most JPA persistence providers offer the option to create the database schema automatically based on the metadata. A class which should be persisted in a database it must be annotated with javax.
Such a class is called Entity. Eclipselihk uses a database table for every entity. Persisted instances of the class will be represented as one row in the table.
All entity classes must define a primary key, must have a non-arg constructor and or not allowed to be final. Keys can be a single field or a combination of fields. JPA allows to auto-generate the primary key in the database via the GeneratedValue annotation.
By default, the table celipselink corresponds to the class name. The fields of the Entity will be saved in the database. JPA can use either your instance variables fields or the corresponding getters and setters to access the fields.
EclipseLink tutorial – introductory EclipseLink tutorial
You are not allowed to mix both methods. If you want to use the setter and eclispelink methods the Java class must follow the Java Bean naming conventions. JPA persists per default all fields of an Entity, if fields should not be saved they must be marked with Transient.
By default each field is mapped to a column with the name of the field. Together with an ID this annotation defines that this value is generated automatically. JPA allows to define relationships between classes, e. Classes can have one to one, one to many, many to one, and many to many relationships with other classes.
A relationship can be bidirectional or unidirectional, e. Within a ttutorial relationship you need to specify the owning side of this relationship in the other class with the attribute “mappedBy”, e. The entity manager javax. EntityManager provides the operations from and to the database, e. In a JavaEE application the entity manager is automatically inserted in the web application. Outside JavaEE you need to manage tutroial entity manager yourself.
Entities which are managed by an Entity Tutlrial will automatically propagate these changes to the database if this happens within a commit statement. If the Entity Manager is closed via close then the managed entities are tutoriial a detached state.
If synchronize them again with the database a Entity Manager provides the merge method.
EclipseLink – Tutorial
The EntityManager is created by the EntityManagerFactory which is configured by the persistence unit. The persistence unit is described via the persistence. A set of entities which are logical connected will be grouped via a persistence unit. EclipseLink supports several Java standards:.
The example later will be using Apache Derby as a database.
Download Derby from http: For details on Derby which is not required for this tutorial please see Apache Derby. Create a Java project “de. Create a folder “lib” and place the required JPA jars and derby. Add the libs to the project classpath. This examples uses EclipseLink specific flags for example via the parameter “eclipselink. The database specified via “javax.
You may want to adjust the path, it currently is based on Linux notations and points to my home directory on my Linux system. To see the SQL generated for the databases set eclipselink.
Two eclkpselink will get generated ‘createDDL. Create the following Main class which will create a new entry every time it is called. After the first call you need to remove the property “eclipselink. Alternative you could set the property to “drop-and-create-tables” eclipse,ink this would drop your database schema at every run. In order to avoid writing too much boilerplate code for the entity classes you can use lombok, which automatically generates appropriate getters, eclipsleink, toString and hashCode methods for the fields in a Java class.
Create a Java project called “de. Create the file “persistence. Eclipselunk to change the path to the database.
The following check is implemented as a JUnit Test. For details please see JUnit Tutorial. The setup method will create a few test entries.
After the test entries are created, they will be read and the one field of the entries is changed and saved to the database. Dynamic, typesafe queries in JPA 2. Free use of the software tutoorial is granted under the terms of the Eclipse Public License 2. This tutorial explains how to use the Java persistence API.
Entity A class which should be persisted in a database it must be annotated with javax. Persistence of fields The fields of the Entity will be saved in the database. Relationship Mapping JPA allows to define relationships between classes, e. Entity Manager The entity manager javax. The persistence context describes all Entities of one Entity manager. Persistence units The EntityManager is created by the EntityManagerFactory which is configured by the persistence unit.
EclipseLink supports several Java standards: Java Persistence JPA 2. Derby Database The example later will be using Apache Derby as a database. Usage of JPA in an Java application 4. Project and Entity Create a Java project “de. Afterwards create the package “de. Entity ; import javax. GeneratedValue ; import javax. GenerationType ; import javax. Test your installation Create the following Main class which will create a new entry every time it is called.
List ; import javax. EntityManager ; import javax. EntityManagerFactory ; import javax. Persistence ; import javax. Query ; import de. Using lombok for entity classes In order to avoid writing too much boilerplate code for the entity classes you can use lombok, which automatically generates appropriate getters, setters, toString and hashCode methods for the fields in a Java class.
Data ; import javax. Relationship example Create a Java project called “de. ArrayList ; import java. Id ; import javax. ManyToOne ; import eclipselnk. OneToMany ; import javax. Query ; import org. Eclipselonk ; import org. Test ; import de. Family ; import de. Links and Literature 7. Field will not be saved in database.