Difference between revisions of "EclipseLink/Examples/MOXy/JPA"

From Eclipsepedia

Jump to: navigation, search
(Many To Many)
(Converting JPA entities to/from XML (via JAXB))
 
(12 intermediate revisions by one user not shown)
Line 1: Line 1:
== Overview ==
+
== Converting JPA entities to/from XML (via JAXB) ==
 
+
JPA provides an easy and powerful means to use Java objects to interact with a relational databaseThese Java objects are called entities, and have their own characteristicsSome of these characteristics (bidirectional relationships, compound keys, embedded key classes, and lazy loading) can cause challenges when mapping these objects to XML.  This example demonstrates how to easily overcome these challenges using EclipseLink MOXy (JAXB):
This example demonstrates how to derive an XML representation from a set of JPA entities using JAXB.  In simplest terms JAXB will be used to apply a tree structure to the object graph of JPA entitiesMultiple tree representations of an object graph are possible and will depend on the root object chosen and the direction the relationships are traversed.
+
* [[EclipseLink/Examples/MOXy/JPA/Relationships | Binding JPA Relationships to XML]]
 
+
* [[EclipseLink/Examples/MOXy/JPA/CompoundPrimaryKeys | Binding Compound Primay Keys to XML]]
== JPA Entities ==
+
* [[EclipseLink/Examples/MOXy/JPA/EmbeddedIdClass | Binding Embedded ID Classes to XML]]
 
+
For this example the following JPA entities will be used.  In order to save space package names, import statements, and the get /set methods have been omitted from the following code samplesAll annotations shown below are standard JPA annotations.
+
 
+
<source lang="java">
+
@Entity
+
public class Department {
+
 
+
    @Id
+
    @Column(name="D_ID")
+
    private BigDecimal dId;
+
 
+
    private String name;
+
+
    @ManyToMany
+
    @JoinTable(name="DEPT_EMP", joinColumns =
+
        @JoinColumn(name="D_ID", referencedColumnName = "D_ID"),  
+
            inverseJoinColumns = @JoinColumn(name="E_ID",
+
                referencedColumnName = "E_ID"))
+
    private List<Employee> member;
+
 
+
}
+
</source>
+
 
+
<source lang="java">
+
@Entity
+
public class Employee {
+
 
+
    @Id
+
    @Column(name="E_ID")
+
    private BigDecimal eId;
+
 
+
    private String name;
+
 
+
    @OneToOne(mappedBy="resident")
+
    private Address residence;
+
 
+
    @OneToMany(mappedBy="contact")
+
    private List<PhoneNumber> contactNumber;
+
 
+
    @ManyToMany(mappedBy="member")
+
    private List<Department> team;
+
 
+
}
+
</source>
+
 
+
<source lang="java">
+
@Entity
+
public class Address {
+
+
    @Id
+
    @Column(name="E_ID", insertable=false, updatable=false)
+
    private BigDecimal eId;
+
 
+
    private String city;
+
 
+
    private String street;
+
 
+
    @OneToOne
+
    @JoinColumn(name="E_ID")
+
    private Employee resident;
+
 
+
}
+
</source>
+
 
+
<source lang="java">
+
@Entity
+
@Table(name="PHONE_NUMBER")
+
public class PhoneNumber {
+
 
+
    @Id
+
    @Column(name="P_ID")
+
    private BigDecimal pId;
+
 
+
    @ManyToOne
+
    @JoinColumn(name="E_ID", referencedColumnName = "E_ID")
+
    private Employee contact;
+
 
+
    private String num;
+
 
+
}
+
</source>
+
 
+
== JAXB Binding ==
+
 
+
For this example the XML acessor type will be set to FIELD for all the model classes.  This can be set as a package level JAXB annotation.
+
 
+
<source lang="java">
+
@XmlAccessorType(XmlAccessType.FIELD)
+
package com.example.model;
+
 
+
import javax.xml.bind.annotation.XmlAccessType;
+
import javax.xml.bind.annotation.XmlAccessorType;
+
</source>
+
 
+
=== Relationships - Privately Owned ===
+
 
+
These relationships apply when the target object(s) is only referenced by a single source object.  This type of relationship can be safely represented as nesting in XML (the default in JAXB).
+
 
+
==== One To One  ====
+
 
+
In JPA the OneToOne annotation indicates that only one instance of the source entity is able to refer to the same target entity instance.  Since the relationship between Employee and Address is bi-directional, we need to mark one side transient in JAXB to prevent a cycle.  In order to populate the relationship between Address and Employee the EclipseLink annotation @XmlContainerProperty can be used.
+
 
+
<source lang="java">
+
@Entity
+
public class Employee {
+
 
+
    @OneToOne(mappedBy="resident")
+
    @XmlContainerProperty("resident")
+
    private Address residence;
+
 
+
}
+
</source>
+
 
+
<source lang="java">
+
@Entity
+
public class Address {
+
+
    @OneToOne
+
    @JoinColumn(name="E_ID")
+
    @XmlTransient
+
    private Employee resident;
+
 
+
}
+
</source>
+
 
+
==== One To Many ====
+
 
+
In JPA the OneToMany annotation indicates that only one instance of the source entity is able to refer to the same target entity instance.  Since the relationship between Employee and Address is bi-directional, we need to mark one side transient in JAXB to prevent a cycle.
+
 
+
<source lang="java">
+
@Entity
+
public class Employee {
+
 
+
    @OneToMany(mappedBy="contact")
+
    private List<PhoneNumber> contactNumber;
+
 
+
}
+
</source>
+
 
+
<source lang="java">
+
@Entity
+
public class PhoneNumber {
+
 
+
    @ManyToOne
+
    @JoinColumn(name="E_ID", referencedColumnName = "E_ID")
+
    @XmlTransient
+
    private Employee contact;
+
 
+
}
+
</source>
+
 
+
=== Relationships - Shared Reference ===
+
 
+
These relationships apply when the target object(s) may be referenced by multiple source objects.  This type of relationship can not be safely represented as nesting in XML.
+
 
+
==== Many To One ====
+
 
+
In JPA the ManyToOne annotation indicates that one or more instances of the source entity are able to refer to the same target entity instance.
+
 
+
<source lang="java">
+
@Entity
+
public class PhoneNumber {
+
 
+
    @ManyToOne
+
    @JoinColumn(name="E_ID", referencedColumnName = "E_ID")
+
    @XmlIDREF
+
    private Employee contact;
+
 
+
}
+
</source>
+
 
+
<source lang="java">
+
@Entity
+
public class Employee {
+
 
+
    @Id
+
    @Column(name="E_ID")
+
    @XmlID
+
    private BigDecimal eId;
+
 
+
    @OneToMany(mappedBy="contact")
+
    private List<PhoneNumber> contactNumber;
+
 
+
}
+
</source>
+
 
+
==== Many To Many ====
+
 
+
In JPA the ManyToMany annotation indicates that one or more instances of the source entity are able to refer to the same target entity instance.
+
 
+
<source lang="java">
+
@Entity
+
public class Department {
+
+
    @ManyToMany
+
    @JoinTable(name="DEPT_EMP", joinColumns =
+
        @JoinColumn(name="D_ID", referencedColumnName = "D_ID"),
+
            inverseJoinColumns = @JoinColumn(name="E_ID",
+
                referencedColumnName = "E_ID"))
+
    @XmlIDREF
+
    private List<Employee> member;
+
 
+
}
+
</source>
+
 
+
<source lang="java">
+
@Entity
+
public class Employee {
+
 
+
    @Id
+
    @Column(name="E_ID")
+
    @XmlId
+
    private BigDecimal eId;
+
 
+
    @ManyToMany(mappedBy="member")
+
    private List<Department> team;
+
 
+
}
+
</source>
+

Latest revision as of 12:34, 29 January 2010

[edit] Converting JPA entities to/from XML (via JAXB)

JPA provides an easy and powerful means to use Java objects to interact with a relational database. These Java objects are called entities, and have their own characteristics. Some of these characteristics (bidirectional relationships, compound keys, embedded key classes, and lazy loading) can cause challenges when mapping these objects to XML. This example demonstrates how to easily overcome these challenges using EclipseLink MOXy (JAXB):