JPA 列定义示例

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;
  }

  @Override
  public 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);
    }

  }
  @PersistenceContext
  private 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: EMP
 Row:
    Column Name: EMP_ID,
    Column Type: BIGINT:
    Column Value: 1
    Column Name: NAME,
    Column Type: VARCHAR:
    Column Value: Tom

    Column Name: SURNAME,
    Column Type: VARCHAR:
    Column Value: Smith

 Row:
    Column Name: EMP_ID,
    Column Type: BIGINT:
    Column Value: 2

    Column Name: NAME,
    Column Type: VARCHAR:
    Column Value: Jack

    Column Name: SURNAME,
    Column Type: VARCHAR:
    Column Value: Kook