Hibernate annotation JPA基础配置(注解配置)

TomasEdision

2010-12-03

关注关注

JPA(Java Persistence API), 是EJB3.0的组成部分, 它显著简化了EJB持续性并提供了一个对象关系映射方法, 该方法使开发者可以采用声明方式定义如何通过一种标准的可移植方式将Java对象映射到关系数据库表.

Hibernate从3.2开始,就开始兼容JPA,可以通过注释的方式,代替原有的xml映射方式.

引入Hibernateannotation后,我们需要进行如下准备,下载依赖的类库.

Hibernatecore3.2+

Hibernateannotation

JPA

【示例】

首先先来看一个使用Annotation后的实体配置:

Company.java
@Entity
@Table(name = "fin_company")
public class Company {

   @Id
   @GeneratedValue(strategy = GenerationType.AUTO)
   private long id;
   
   @Column(name = "c_name", length = 50, nullable = false)
   private String name;
   
   @Column(columnDefinition = "text")
   private String description;
   
   @OneToMany(mappedBy = "company", fetch = FetchType.LAZY, cascade = CascadeType.REMOVE)
   private List<Employee> employees;

   public Company() {
      this.employees = new ArrayList<Employee>();
   }

   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 getDescription() {
      return description;
   }

   public void setDescription(String description) {
      this.description = description;
   }

   public List<Employee> getEmployees() {
      return employees;
   }

   public void setEmployees(List<Employee> employees) {
      this.employees = employees;
   }
}

Employee.java
@Entity
@Table(name = "fin_employee")
public class Employee {

   private long id;
   private String name;
   private Company company;

   @Id
   @GeneratedValue(strategy = GenerationType.AUTO)
   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;
   }

   @ManyToOne(fetch = FetchType.LAZY)
   @JoinColumn(name = "company_id")
   public Company getCompany() {
      return company;
   }

   public void setCompany(Company company) {
      this.company = company;
   }
   
   @Transient
   public String getCompanyName() {
      return this.company.getName();
   }
}

在上面的Java类中, 我们可以看到, 所有以@开头的标注都是JPA标注, JPA标注可以写在属性名前, 也可以写在属性的get方法前. 接下来逐一介绍这些基本标注的意思.

【注释说明】

@Entity

将普通的Java类指定为实体,默认情况下,所有Java类为非持续化类@Table

指定映射数据表名, 默认情况下以类名作为数据表名, 如非特殊指定, 可以省略该注释项

@Id

@GeneratedValue(strategy=GenerationType.AUTO)

privatelongid;

指定该实体的主键字段, 并且主键的增长方式有JAP选择最适合于基础数据库的主键生成器

@Column(name = "c_name", length = 50, nullable = false)

privateStringname;

name:默认情况下,JPA会根据属性名生成数据表字段名,使用name属性进行特殊指定