JPA映射关系

我会带着你远行 2023-05-31 10:09 16阅读 0赞

### JPA映射关系 ###

*  单向
 *   *  一对一
     *  多对一
     *  一对多
 *  双向
 *   *  一对多/多对一

# 单向 #

## 一对一 ##

实体:

@Entity
    @Table(name="tb_product")
    public class Product {
    	@Id
    	@GeneratedValue(strategy=GenerationType.IDENTITY)
    	private Long id;
    	private String name;
    	@OneToOne
    	@JoinColumn(name="dir_id")
    	private ProductDir dirId;
    	/**
    	 * @return the id
    	 */
    	public Long getId() {
    		return id;
    	}
    	/**
    	 * @param id the id to set
    	 */
    	public void setId(Long id) {
    		this.id = id;
    	}
    	/**
    	 * @return the name
    	 */
    	public String getName() {
    		return name;
    	}
    	/**
    	 * @param name the name to set
    	 */
    	public void setName(String name) {
    		this.name = name;
    	}
    	
    	/**
    	 * @return the dirId
    	 */
    	public ProductDir getDirId() {
    		return dirId;
    	}
    	/**
    	 * @param dirId the dirId to set
    	 */
    	public void setDirId(ProductDir dirId) {
    		this.dirId = dirId;
    	}
    	/** 
    	 * @Title: toString
    	 * @author zjh
    	 * @Desc: 
    	 * @return 
    	 * @see java.lang.Object#toString() 
    	 */
    	@Override
    	public String toString() {
    		return "Product [id=" + id + ", name=" + name + ", dirId=" + dirId
    				+ "]";
    	}
    }

@Entity
    @Table(name="tb_productDir")
    public class ProductDir {
    	@Id
    	@GeneratedValue(strategy=GenerationType.IDENTITY)
    	private Long id;
    	private String name;
    	/**
    	 * @return the id
    	 */
    	public Long getId() {
    		return id;
    	}
    	/**
    	 * @param id the id to set
    	 */
    	public void setId(Long id) {
    		this.id = id;
    	}
    	/**
    	 * @return the name
    	 */
    	public String getName() {
    		return name;
    	}
    	/**
    	 * @param name the name to set
    	 */
    	public void setName(String name) {
    		this.name = name;
    	}
    	/** 
    	 * @Title: toString
    	 * @author zjh
    	 * @Desc: 
    	 * @return 
    	 * @see java.lang.Object#toString() 
    	 */
    	@Override
    	public String toString() {
    		return "ProductDir [id=" + id + ", name=" + name + "]";
    	}
    }

测试

public class TestDemo {
    	IProductDao iProductDao = new ProductDaoImpl();
    	IProductDirDao iProductDirDao =  new ProductDirDaoImpl();
    	@org.junit.Test
    	public void Test(){
    		ProductDir productDir = new ProductDir();
    		productDir.setName("食品");
    		Product product = new Product();
    		product.setName("牛肉");
    		product.setDirId(productDir);
    		
    		iProductDirDao.save(productDir);
    		iProductDao.save(product);
    	}
    }

控制台打印

Hibernate: insert into tb_productDir (name) values (?)
    Hibernate: insert into tb_product (dir_id, name) values (?, ?)

## 多对一 ##

一的实体

## 一对多 ##

一的实体

@Entity
    public class Teacher {
    	@Id
    	@GeneratedValue(strategy = GenerationType.IDENTITY)
    	private Long id;
    	private String name;
    	@OneToMany
    	//这里如果是要一对多关系模式的话，必须加上JoinColumn()注解，否则会生成一张关联表，那样的话就会被误解为多对多
    	@JoinColumn(name="student_id")
    	private List<Student> students = new ArrayList<>();
    	/**
    	 * @return the id
    	 */
    	public Long getId() {
    		return id;
    	}
    	/**
    	 * @param id the id to set
    	 */
    	public void setId(Long id) {
    		this.id = id;
    	}
    	/**
    	 * @return the name
    	 */
    	public String getName() {
    		return name;
    	}
    	/**
    	 * @param name the name to set
    	 */
    	public void setName(String name) {
    		this.name = name;
    	}
    	/**
    	 * @return the students
    	 */
    	public List<Student> getStudents() {
    		return students;
    	}
    	/**
    	 * @param students the students to set
    	 */
    	public void setStudents(List<Student> students) {
    		this.students = students;
    	}
    	/** 
    	 * @Title: toString
    	 * @author zjh
    	 * @Desc: 
    	 * @return 
    	 * @see java.lang.Object#toString() 
    	 */
    	@Override
    	public String toString() {
    		return "Teacher [id=" + id + ", name=" + name + "]";
    	}
    }

多的实体

@Entity
    public class Student {
    	@Id
    	@GeneratedValue(strategy = GenerationType.IDENTITY)
    	private Long id;
    	private String name;
    	/**
    	 * @return the id
    	 */
    	public Long getId() {
    		return id;
    	}
    	/**
    	 * @param id the id to set
    	 */
    	public void setId(Long id) {
    		this.id = id;
    	}
    	/**
    	 * @return the name
    	 */
    	public String getName() {
    		return name;
    	}
    	/**
    	 * @param name the name to set
    	 */
    	public void setName(String name) {
    		this.name = name;
    	}
    	/** 
    	 * @Title: toString
    	 * @author zjh
    	 * @Desc: 
    	 * @return 
    	 * @see java.lang.Object#toString() 
    	 */
    	@Override
    	public String toString() {
    		return "Student [id=" + id + ", name=" + name + "]";
    	}
    }

测试代码

public class OneToManyTest {
    	@Test
    	public void testAdd(){
    		Student student = new Student();
    		student.setName("tom");
    		Student student2 = new Student();
    		student2.setName("jreey");
    		
    		Teacher teacher = new Teacher();
    		teacher.setName("jack");
    		teacher.getStudents().add(student);
    		teacher.getStudents().add(student2);
    		
    		EntityManagerFactory entityManagerFactory = JPAUtils.getEntityManagerFactory();
    		EntityManager createEntityManager = entityManagerFactory.createEntityManager();
    		EntityTransaction transaction = createEntityManager.getTransaction();
    		transaction.begin();
    		createEntityManager.persist(teacher);
    		createEntityManager.persist(student);
    		createEntityManager.persist(student2);
    		
    		transaction.commit();
    		createEntityManager.close();
    	}
    }

日志

Hibernate: insert into Teacher (name) values (?)
    Hibernate: insert into Student (name) values (?)
    Hibernate: insert into Student (name) values (?)
    Hibernate: update Student set student_id=? where id=?
    Hibernate: update Student set student_id=? where id=?

# 双向 #

## 一对多/多对一 ##