JPA教程 - JPA列定义示例

当将Java bean映射到实体时，我们可以在映射注释中设置数据库表列定义。

以下代码将列定义设置为 VARCHAR(40)。

@Column(columnDefinition = "VARCHAR(40)")
private String name;

@Column注释表示物理数据库列的特定特征。

例子

下面的代码来自Person.java。

package cn.w3cschool.common;
import static javax.persistence.FetchType.LAZY;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.Table;@Entity
@Table(name="EMP")
public class Person {@Id@Column(name = "EMP_ID")private long id;@Column(columnDefinition = "VARCHAR(40)")private String name;private String surname;public Person() {}public Person(String name, String surname) {this.name = name;this.surname = surname;}public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSurname() {return surname;}public void setSurname(String surname) {this.surname = surname;}@Overridepublic String toString() {return "Person [id=" + id + ", name=" + name + ", surname=" + surname + "]";}
}

这里是显示如何使用Person实体的代码。

package cn.w3cschool.common;import java.util.List;import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;import org.springframework.transaction.annotation.Transactional;@Transactional
public class PersonDaoImpl {public void test(){Person p1 = new Person("Tom", "Smith");p1.setId(1L);Person p2 = new Person("Jack", "Kook");p2.setId(2L);save(p1);save(p2);listAll();}private void listAll(){List<Person> persons = getAll();for (Person person : persons) {System.out.println(person);}}@PersistenceContextprivate EntityManager em;public Long save(Person person) {em.persist(person);return person.getId();}public List<Person>getAll() {return em.createQuery("SELECT p FROM Person p", Person.class).getResultList();}}

下载 Column_Definition.zip

这里是运行上面的代码的结果。

以下是数据库表转储。

Table Name: EMPRow:Column Name: EMP_ID,Column Type: BIGINT:Column Value: 1Column Name: NAME,Column Type: VARCHAR:Column Value: TomColumn Name: SURNAME,Column Type: VARCHAR:Column Value: SmithRow:Column Name: EMP_ID,Column Type: BIGINT:Column Value: 2Column Name: NAME,Column Type: VARCHAR:Column Value: JackColumn Name: SURNAME,Column Type: VARCHAR:Column Value: Kook