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