java - org.hibernate.dialect.OracleDialect does not support identity key generation

Question

I was trying to import a sample project in to eclipse and was facing the below given error up on running the application.

Caused by: org.hibernate.MappingException: org.hibernate.dialect.OracleDialect does not support identity key generation
    at org.hibernate.dialect.Dialect.getIdentityColumnString(Dialect.java:743)
    at org.hibernate.dialect.Dialect.getIdentityColumnString(Dialect.java:733)
    at org.hibernate.mapping.Table.sqlCreateString(Table.java:426)
    at org.hibernate.cfg.Configuration.generateSchemaCreationScript(Configuration.java:1028)
    at org.hibernate.tool.hbm2ddl.SchemaExport.<init>(SchemaExport.java:125)
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:492)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1744)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1782)
    at org.springframework.orm.hibernate4.LocalSessionFactoryBuilder.buildSessionFactory(LocalSessionFactoryBuilder.java:247)
    at org.springframework.orm.hibernate4.LocalSessionFactoryBean.buildSessionFactory(LocalSessionFactoryBean.java:373)
    at org.springframework.orm.hibernate4.LocalSessionFactoryBean.afterPropertiesSet(LocalSessionFactoryBean.java:358)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1541)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1479)
    ... 32 more

As per this SO link, I have changed the

@GeneratedValue(strategy = GenerationType.IDENTITY)

to

@GeneratedValue(strategy = GenerationType.AUTO) or @GeneratedValue(strategy = GenerationType.TABLE)

But didn't work.

Here is the code:

User.java:

@Entity
@Table(name = "users")
@ManagedBean
@ViewScoped
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "username", nullable = false)
    private String username;

    @Column(name = "password", nullable = false)
    private String password;

    @Column(name = "role", nullable = false)
    private String role;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getRole() {
        return role;
    }

    public void setRole(String role) {
        this.role = role;
    }

    }

From the applicationContext.xml:

<!-- Session Factory Declaration -->
<bean id="SessionFactory"
    class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
    <property name="dataSource" ref="DataSource" />
    <property name="annotatedClasses">
        <list>
            <value>com.crud.model.User</value>
        </list>
    </property>
    <property name="hibernateProperties">
        <props>
            <prop key="hibernate.dialect">org.hibernate.dialect.OracleDialect</prop>
            <prop key="hibernate.show_sql">true</prop>
            <prop key="hibernate.hbm2ddl.auto">create</prop>

        </props>
    </property>
</bean>

Answer 1

You can use tell Hibernate to use a sequence to generate your ID's

@Id
@Column(name = "ID")
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator = "id_Sequence")
@SequenceGenerator(name = "id_Sequence", sequenceName = "ID_SEQ")
private int id;

This config basically tells Hibernate to use a database sequence called ID_SEQ to generate the ID's for this object. You can specify other sequences on other objects if you want other unique ID's or you can use the same sequence if you want globally unique ID's across your entire system.

The only downside to this is that can't perform batch inserts (without some further config) because Hibernate needs to get the next sequence value from the database every time, and you can't use this config if you want to use a MySQL database, because they don't support sequences.

If any of that doesn't make sense let me know and I'll explain it further.