近三天jpa学习
创建完persistence.xml后，需要对数据库中表进行entity映射，当然，也可以不事先创建表，使用在persistence中的配置来自动创建数据库中的表。我创建了两个实体entity，这两个实体entity我已经在数据库中事先创建好表和他们对应。
testuser类
import java.util.Date;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Cacheable;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.TableGenerator;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;
import com.tao3c.dao.impl.TestUserDaoImpl;
@Entity
@Table(name = "test_user")
@Cacheable
@Cache(usage = CacheConcurrencyStrategy.TRANSACTIONAL, region = "com.XXX.entity.TestUserEntity")
@NamedQueries({
@NamedQuery(name=TestUserDaoImpl.QUERY_GETALLTESTUSER,query=TestUserDaoImpl.TESTUSER_GETALLUSER),
@NamedQuery(name=TestUserDaoImpl.QUERY_GETTESTUSERBYCONDITION,query=TestUserDaoImpl.TESTUSER_GETUSERBYCONDITION),
@NamedQuery(name=TestUserDaoImpl.QUERY_GETTESTUSERNORELATIONJOIN,query=TestUserDaoImpl.TESTUSER_GETNORELATIONJOIN)
})
public class TestUserEntity extends AbstractBaseEntity {
private static final long serialVersionUID = -7139178611703146047L;
public TestUserEntity(){
this.emails = new HashSet<TestEmailEntity>();
}
/**
* int TestUserEntity.java $id值
*/
@Id
@TableGenerator(name = "TestUserGenerator", table = "id_testuser", pkColumnName = "GEN_KEY", pkColumnValue = "com.tao3c.testuser", valueColumnName = "GEN_VALUE", allocationSize = 10, initialValue = 11)
@GeneratedValue(strategy = GenerationType.TABLE, generator = "TestUserGenerator")
@Column(name = "id", unique = true, nullable = false)
private int id;
@Column(name = "name")
private String name;
@Temporal(TemporalType.DATE)
private Date regtime;
@OneToMany(cascade={CascadeType.PERSIST,CascadeType.REFRESH,CascadeType.REMOVE,CascadeType.MERGE},mappedBy="testuser")
private Set<TestEmailEntity> emails;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Date getRegtime() {
return regtime;
}
public void setRegtime(Date regtime) {
this.regtime = regtime;
}
public Set<TestEmailEntity> getEmails() {
return emails;
}
public void setEmails(Set<TestEmailEntity> emails) {
this.emails = emails;
}
public void addTestEmail(TestEmailEntity entity){
this.emails.add(entity);
}
}testemails类
import javax.persistence.Cacheable;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Id;
import javax.persistence.Table;
import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;
@Entity
@Table(name="test_emails")
@Cacheable
@Cache(usage = CacheConcurrencyStrategy.TRANSACTIONAL, region = "com.XXX.entity.TestUserEntity")
public class TestEmailEntity {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name="id")
private int id;
@Column(name="userid")
private int userid;
@Column(name="emailname")
private String emailname;
@ManyToOne(cascade={CascadeType.MERGE,CascadeType.REFRESH,CascadeType.PERSIST,CascadeType.REMOVE},optional=false)
@JoinColumn(name="user_id")
private TestUserEntity testuser;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getUserid() {
return userid;
}
public void setUserid(int userid) {
this.userid = userid;
}
public String getEmailname() {
return emailname;
}
public void setEmailname(String emailname) {
this.emailname = emailname;
}
public TestUserEntity getTestuser() {
return testuser;
}
public void setTestuser(TestUserEntity testuser) {
this.testuser = testuser;
}
}首先说明下，在testuser类中可以存在多个testemail 用来测试jpa的一对多和多对已的关系。
在testuser中
@Entity
@Table(name = "test_user")
@Cacheable
@Cache(usage = CacheConcurrencyStrategy.TRANSACTIONAL, region = "com.XXX.entity.TestUserEntity")
@NamedQueries({
@NamedQuery(name=TestUserDaoImpl.QUERY_GETALLTESTUSER,query=TestUserDaoImpl.TESTUSER_GETALLUSER),
@NamedQuery(name=TestUserDaoImpl.QUERY_GETTESTUSERBYCONDITION,query=TestUserDaoImpl.TESTUSER_GETUSERBYCONDITION),
@NamedQuery(name=TestUserDaoImpl.QUERY_GETTESTUSERNORELATIONJOIN,query=TestUserDaoImpl.TESTUSER_GETNORELATIONJOIN)
})entity声明这是一个实体类，table声明了数据库中表的名称，如果不使用缓存策略的话可以将cacheable和cache去除，在cache中的region声明了缓存策略，这是在配置文件中配置的。namedqueries中事先定义了所要使用的sql，在查询中是使用类似于这样的语句进行查询
Query query = entityManager.createNamedQuery(QUERY_GETTESTUSERBYCONDITION);
同样也可以使用原生的jpql进行查询，直接使用jpql进行查询使代码看起来不简洁，对以后的维护不利。
/** * int TestUserEntity.java $id值 */ @Id @TableGenerator(name = "TestUserGenerator", table = "id_testuser", pkColumnName = "GEN_KEY", pkColumnValue = "com.tao3c.testuser", valueColumnName = "GEN_VALUE", allocationSize = 10, initialValue = 11) @GeneratedValue(strategy = GenerationType.TABLE, generator = "TestUserGenerator") @Column(name = "id", unique = true, nullable = false) private int id;
在这里id声明了entity的主键，TableGenerator对应于GeneratedValue中的generator，因为使用的主键生成策略是GenerationType.TABlE 既它的id键值是通过数据库中的一个表来生成的，这个你表的名字为id_testuser 该表有两个字段分别为gen_key 和gen_value 其实这个表中只需要一列就可以了， gen_key的值变为com.tao3c.testuser，gen_value的起始值为11，如果在这个表中没有11这一行，那么hibernate的实现中对initValue值是不起作用的这就需要自己手动的将该行插入到表中，设置gen_value的值为11,allocationSize 为每次取出多少的id值供后续使用，该属性不能取的太大，如果你频繁重启服务器的话，就会使id的值以allocationSize间隔跳跃。
@Temporal(TemporalType.DATE) private Date regtime;
为时间字段的映射
.......后续的内容在写了，先干活l