JPA: Mapping to an existing database IS-907 Java EE JPA: Mapping to an existing database

Mapping entities to existing databases We have seen how JPA automatically maps classes to tables To map a class model to an existing database more detailed control over the mapping may be needed http://download.oracle.com/javaee/6/api/ package javax.persistence, Annotation Types Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

Table names Tablename, schema and catalog can optionally be specified with a @Table annotation: @Entity @Table(name=“tablename””, schema=“schema”, catalog=“catalog”) public class Employee { ... } Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

Columns Column properties are specified with column annotation: @Entity public class Employee { @Id private long empId; @Column(name=“login”, unique=“true”, nullable=“false”) private String username; ... } Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

Large objects The @Lob annotation is used to map fields to CLOBs or BLOBs byte[], Byte[], and Serializable classes are mapped to BLOB char[], Character[], and String are mapped to CLOB @Entity public class Employee { @Lob byte[] speech; @Lob Picture picture; @Lob String biography; } Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

@Basic annotation Fetching of field values can be deferred until the field is actually needed, to speed up loading of data: @Entity public class Employee { @Basic(fetch=“FetchType.LAZY”) @Lob private byte[] picture; ... } Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

Temporal types The mapping of Date and Calendar fields can be controlled with @Temporal annotations: @Entity public class Employee { @Temporal(TemporalType.DATE) private Calendar birthDate; @Temporal(TemporalType.TIMESTAMP) private Timestamp lastLogin; } Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

Foreign keys The name of foreign key columns can be specified with a JoinColumn annotation: @Entity public class Employee { @ManyToOne @JoinColumn(name=“dep”, nullable=“false”, unique=“false”) private Department dep; ... } Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

Join tables @Entity public class Project { @ManyToMany @JoinTable(name=“proj_emp” joinColumns=@JoinColumn(name=“projno”), inverseJoinColumns=@JoinColumn(name=“empid”)) private List<Employee> members; ... } Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

Ordered list @Entity public class Project { @ManyToMany @OrderBy(“name ASC”) private List<Employee> members; ... } Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

Using a Map instead of a List @Entity public class Project { @ManyToMany @MapKey(name=“name”) private Map<String,Employee> members; ... } Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

Lazy relationships Loading of related objects may be deferred by specifying fetch type: @Entity public class Employee { @ManyToOne(fetch=“FetchType.LAZY”) private Department department; ... } Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon

Cascading @Entity public class Order { @OneToMany(cascade={CascadeType.PERSIST, CascadType.MERGE}) List<OrderLine> lines; } ALL DETACH MERGE PERSIST REFRESH REMOVE Even Åby Larsen (even.larsen@uia.no) IS-102 Introduksjon