We began this chapter with the goal of mapping the following object model:
That goal has now been met. In the course of explaining JPA's object-relational mapping metadata, we slowly built the requisite schema and mappings for the complete model. First, the database schema:
And finally, the complete entity mappings. We have trimmed the mappings to take advantage of JPA defaults where possible.
Example 13.17. Full Entity Mappings
package org.mag; @Entity @IdClass(Magazine.MagazineId.class) @Table(name="MAG") @DiscriminatorValue("Mag") public class Magazine { @Column(length=9) @Id private String isbn; @Id private String title; @Column(name="VERS") @Version private int version; private String name; private double price; @Column(name="COPIES") private int copiesSold; @OneToOne(fetch=FetchType.LAZY, cascade={CascadeType.PERSIST,CascadeType.REMOVE}) @JoinColumn(name="COVER_ID") private Article coverArticle; @OneToMany(cascade={CascadeType.PERSIST,CascadeType.REMOVE}) @OrderBy @JoinTable(name="MAG_ARTS", joinColumns={ @JoinColumn(name="MAG_ISBN", referencedColumnName="ISBN"), @JoinColumn(name="MAG_TITLE", referencedColumnName="TITLE") }, inverseJoinColumns=@JoinColumn(name="ART_ID")) private Collection<Article> articles; @ManyToOne(fetch=FetchType.LAZY, cascade=CascadeType.PERSIST) @JoinColumn(name="PUB_ID") private Company publisher; @Transient private byte[] data; ... public static class MagazineId { ... } } @Entity @Table(name="ART", uniqueConstraints=@Unique(columnNames="TITLE")) @SequenceGenerator(name="ArticleSeq", sequenceName="ART_SEQ") public class Article { @Id @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="ArticleSeq") private long id; @Column(name="VERS") @Version private int version; private String title; private byte[] content; @ManyToMany(cascade=CascadeType.PERSIST) @OrderBy("lastName, firstName") @JoinTable(name="ART_AUTHS", joinColumns=@JoinColumn(name="ART_ID"), inverseJoinColumns=@JoinColumn(name="AUTH_ID")) private Collection<Author> authors; ... } package org.mag.pub; @Entity @Table(name="COMP") public class Company { @Column(name="CID") @Id private long id; @Column(name="VERS") @Version private int version; private String name; @Column(name="REV") private double revenue; @Embedded @AttributeOverrides({ @AttributeOverride(name="street", column=@Column(name="STRT")), @AttributeOverride(name="city", column=@Column(name="ACITY")) }) private Address address; @OneToMany(mappedBy="publisher", cascade=CascadeType.PERSIST) private Collection<Magazine> mags; @OneToMany(cascade=CascadeType.PERSIST,CascadeType.REMOVE) @JoinTable(name="COMP_SUBS", joinColumns=@JoinColumn(name="COMP_ID"), inverseJoinColumns=@JoinColumn(name="SUB_ID")) private Collection<Subscription> subscriptions; ... } @Entity @Table(name="AUTH") public class Author { @Id @GeneratedValue(strategy=GenerationType.TABLE, generator="AuthorGen") @TableGenerator(name="AuthorGen", tableName="AUTH_GEN", pkColumnName="PK", valueColumnName="AID") @Column(name="AID", columnDefinition="INTEGER64") private long id; @Column(name="VERS") @Version private int version; @Column(name="FNAME") private String firstName; @Column(name="LNAME") private String lastName; private Address address; @ManyToMany(mappedBy="authors", cascade=CascadeType.PERSIST) private Collection<Article> arts; ... } @Embeddable public class Address { private String street; private String city; @Column(columnDefinition="CHAR(2)") private String state; private String zip; } package org.mag.subscribe; @MappedSuperclass public abstract class Document { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private long id; @Column(name="VERS") @Version private int version; ... } @Entity @Table(schema="CNTRCT") @Inheritance(strategy=InheritanceType.JOINED) @DiscriminatorColumn(name="CTYPE") public class Contract extends Document { @Lob private String terms; ... } @Entity @Table(name="SUB", schema="CNTRCT") @DiscriminatorColumn(name="KIND", discriminatorType=DiscriminatorType.INTEGER) @DiscriminatorValue("1") public class Subscription { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private long id; @Column(name="VERS") @Version private int version; @Column(name="START") private Date startDate; @Column(name="PAY") private double payment; @OneToMany(cascade={CascadeType.PERSIST,CascadeType.REMOVE}) @MapKey(name="num") @JoinTable(name="SUB_ITEMS", schema="CNTRCT", joinColumns=@JoinColumn(name="SUB_ID"), inverseJoinColumns=@JoinColumn(name="ITEM_ID")) private Map<Long,LineItem> items; ... @Entity @Table(name="LINE_ITEM", schema="CNTRCT") public static class LineItem extends Contract { @Column(name="COMM") private String comments; private double price; private long num; @ManyToOne @JoinColumns({ @JoinColumn(name="MAG_ISBN", referencedColumnName="ISBN"), @JoinColumn(name="MAG_TITLE", referencedColumnName="TITLE") }) private Magazine magazine; ... } } @Entity(name="Lifetime") @DiscriminatorValue("2") public class LifetimeSubscription extends Subscription { @Basic(fetch=FetchType.LAZY) @Column(name="ELITE") private boolean getEliteClub() { ... } public void setEliteClub(boolean elite) { ... } ... } @Entity(name="Trial") @DiscriminatorValue("3") public class TrialSubscription extends Subscription { @Column(name="END") public Date getEndDate() { ... } public void setEndDate(Date end) { ... } ... }
The same metadata expressed in XML form:
<entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm orm_1_0.xsd" version="1.0"> <mapped-superclass class="org.mag.subscribe.Document"> <attributes> <id name="id"> <generated-value strategy="IDENTITY"/> </id> <version name="version"> <column name="VERS"/> </version> </attributes> </mapped-superclass> <entity class="org.mag.Magazine"> <table name="MAG"/> <id-class="org.mag.Magazine.MagazineId"/> <discriminator-value>Mag</discriminator-value> <attributes> <id name="isbn"> <column length="9"/> </id> <id name="title"/> <basic name="name"/> <basic name="price"/> <basic name="copiesSold"> <column name="COPIES"/> </basic> <version name="version"> <column name="VERS"/> </version> <many-to-one name="publisher" fetch="LAZY"> <join-column name="PUB_ID"/> <cascade> <cascade-persist/> </cascade> </many-to-one> <one-to-many name="articles"> <order-by/> <join-table name="MAG_ARTS"> <join-column name="MAG_ISBN" referenced-column-name="ISBN"/> <join-column name="MAG_TITLE" referenced-column-name="TITLE"/> <inverse-join-column name="ART_ID"/> </join-table> <cascade> <cascade-persist/> <cascade-remove/> </cascade> </one-to-many> <one-to-one name="coverArticle" fetch="LAZY"> <join-column name="COVER_ID"/> <cascade> <cascade-persist/> <cascade-remove/> </cascade> </one-to-one> <transient name="data"/> </attributes> </entity> <entity class="org.mag.Article"> <table name="ART"> <unique-constraint> <column-name>TITLE</column-name> </unique-constraint> </table> <sequence-generator name="ArticleSeq", sequenceName="ART_SEQ"/> <attributes> <id name="id"> <generated-value strategy="SEQUENCE" generator="ArticleSeq"/> </id> <basic name="title"/> <basic name="content"/> <version name="version"> <column name="VERS"/> </version> <many-to-many name="articles"> <order-by>lastName, firstName</order-by> <join-table name="ART_AUTHS"> <join-column name="ART_ID" referenced-column-name="ID"/> <inverse-join-column name="AUTH_ID" referenced-column-name="AID"/> </join-table> </many-to-many> </attributes> </entity> <entity class="org.mag.pub.Company"> <table name="COMP"/> <attributes> <id name="id"> <column name="CID"/> </id> <basic name="name"/> <basic name="revenue"> <column name="REV"/> </basic> <version name="version"> <column name="VERS"/> </version> <one-to-many name="mags" mapped-by="publisher"> <cascade> <cascade-persist/> </cascade> </one-to-many> <one-to-many name="subscriptions"> <join-table name="COMP_SUBS"> <join-column name="COMP_ID"/> <inverse-join-column name="SUB_ID"/> </join-table> <cascade> <cascade-persist/> <cascade-remove/> </cascade> </one-to-many> <embedded name="address"> <attribute-override name="street"> <column name="STRT"/> </attribute-override> <attribute-override name="city"> <column name="ACITY"/> </attribute-override> </embedded> </attributes> </entity> <entity class="org.mag.pub.Author"> <table name="AUTH"/> <attributes> <id name="id"> <column name="AID" column-definition="INTEGER64"/> <generated-value strategy="TABLE" generator="AuthorGen"/> <table-generator name="AuthorGen" table="AUTH_GEN" pk-column-name="PK" value-column-name="AID"/> </id> <basic name="firstName"> <column name="FNAME"/> </basic> <basic name="lastName"> <column name="LNAME"/> </basic> <version name="version"> <column name="VERS"/> </version> <many-to-many name="arts" mapped-by="authors"> <cascade> <cascade-persist/> </cascade> </many-to-many> <embedded name="address"/> </attributes> </entity> <entity class="org.mag.subcribe.Contract"> <table schema="CNTRCT"/> <inheritance strategy="JOINED"/> <discriminator-column name="CTYPE"/> <attributes> <basic name="terms"> <lob/> </basic> </attributes> </entity> <entity class="org.mag.subcribe.Subscription"> <table name="SUB" schema="CNTRCT"/> <inheritance strategy="SINGLE_TABLE"/> <discriminator-value>1</discriminator-value> <discriminator-column name="KIND" discriminator-type="INTEGER"/> <attributes> <id name="id"> <generated-value strategy="IDENTITY"/> </id> <basic name="payment"> <column name="PAY"/> </basic> <basic name="startDate"> <column name="START"/> </basic> <version name="version"> <column name="VERS"/> </version> <one-to-many name="items"> <map-key name="num"> <join-table name="SUB_ITEMS" schema="CNTRCT"> <join-column name="SUB_ID"/> <inverse-join-column name="ITEM_ID"/> </join-table> <cascade> <cascade-persist/> <cascade-remove/> </cascade> </one-to-many> </attributes> </entity> <entity class="org.mag.subscribe.Subscription.LineItem"> <table name="LINE_ITEM" schema="CNTRCT"/> <attributes> <basic name="comments"> <column name="COMM"/> </basic> <basic name="price"/> <basic name="num"/> <many-to-one name="magazine"> <join-column name="MAG_ISBN" referenced-column-name="ISBN"/> <join-column name="MAG_TITLE" referenced-column-name="TITLE"/> </many-to-one> </attributes> </entity> <entity class="org.mag.subscribe.LifetimeSubscription" name="Lifetime"> <discriminator-value>2</discriminator-value> <attributes> <basic name="eliteClub" fetch="LAZY"> <column name="ELITE"/> </basic> </attributes> </entity> <entity class="org.mag.subscribe.TrialSubscription" name="Trial"> <discriminator-value>3</discriminator-value> <attributes> <basic name="endDate"> <column name="END"/> </basic> </attributes> </entity> <embeddable class="org.mag.pub.Address"> <attributes> <basic name="street"/> <basic name="city"/> <basic name="state"> <column column-definition="CHAR(2)"/> </basic> <basic name="zip"/> </attributes> </embeddable> </entity-mappings>