JPA 系列教程5-双向一对多

时间：2023-03-09 00:08:46
JPA 系列教程5-双向一对多

双向一对多的ddl语句

同单向多对一，单向一对多表的ddl语句一致

Product

package com.jege.jpa.one2many;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.Table;

/**

 * @author JE哥

 * @email 1272434821@qq.com

 * @description:双向:多个商品属于同一个商品类型

 */

@Entity

@Table(name = "t_product")

public class Product {

  @Id

  @GeneratedValue

  private Long id;

  private String name;

  // 多对一

  // optional=false表示外键type_id不能为空

  @ManyToOne(optional = true)

  @JoinColumn(name = "type_id")

  private ProductType type;

  public Product() {

  }

  public Product(String name, ProductType type) {

    this.name = name;

    this.type = type;

  }

  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 ProductType getType() {

    return type;

  }

  public void setType(ProductType type) {

    this.type = type;

  }

  @Override

  public String toString() {

    return "Product [id=" + id + ", name=" + name + "]";

  }

}

ProductType

package com.jege.jpa.one2many;

import java.util.HashSet;

import java.util.Set;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.OneToMany;

import javax.persistence.Table;

/**

 * @author JE哥

 * @email 1272434821@qq.com

 * @description:双向：一个商品类型下面有n个商品

 */

@Entity

@Table(name = "t_product_type")

public class ProductType {

  @Id

  @GeneratedValue

  private Long id;

  private String name;

  // 一对多:集合Set

  @OneToMany(mappedBy = "type", orphanRemoval = true)

  private Set<Product> products = new HashSet<Product>();

  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 Set<Product> getProducts() {

    return products;

  }

  public void setProducts(Set<Product> products) {

    this.products = products;

  }

  @Override

  public String toString() {

    return "ProductType [id=" + id + ", name=" + name + "]";

  }

}

One2ManyTest

package com.jege.jpa.one2many;

import java.util.Set;

import javax.persistence.EntityManager;

import javax.persistence.EntityManagerFactory;

import javax.persistence.Persistence;

import javax.persistence.Query;

import org.junit.After;

import org.junit.AfterClass;

import org.junit.Before;

import org.junit.BeforeClass;

import org.junit.Test;

/**

 * @author JE哥

 * @email 1272434821@qq.com

 * @description:双向一对多Test

 */

public class One2ManyTest {

  private static EntityManagerFactory entityManagerFactory = null;

  private EntityManager entityManager = null;

  @BeforeClass

  public static void setUpBeforeClass() throws Exception {

    entityManagerFactory = Persistence.createEntityManagerFactory("com.jege.jpa");

  }

  // 一次性保存1一个商品类型，保存这个商品类型下面的2个商品

  // 多对一保存的时候必须先保存一方，否则会出现多余的update语句，从而影响性能

  @Before

  public void persist() throws Exception {

    entityManager = entityManagerFactory.createEntityManager();

    entityManager.getTransaction().begin();

    ProductType type = new ProductType();

    type.setName("商品类型1");

    Product product1 = new Product("商品1", type);

    Product product2 = new Product("商品2", type);

    entityManager.persist(type);// 持久化状态 商品类型1

    entityManager.persist(product1);// 持久化状态

    entityManager.persist(product2);// 持久化状态

    entityManager.getTransaction().commit();

    System.out.println("++++++++++++++++++++");

  }

  // 级联保存

  // 需要先修改ProductType.java类

  // @OneToMany(mappedBy = "type",cascade=CascadeType.PERSIST)

  @Test

  public void persist2() throws Exception {

    entityManager = entityManagerFactory.createEntityManager();

    entityManager.getTransaction().begin();

    ProductType type = new ProductType();

    type.setName("商品类型1");

    // 建立多方到一方的关系

    Product product1 = new Product("商品1", type);

    Product product2 = new Product("商品2", type);

    // 从一方建立到多方的关系

    type.getProducts().add(product1);

    type.getProducts().add(product2);// 临时状态

    entityManager.persist(type);// 持久化状态

    entityManager.getTransaction().commit();

  }

  // 级联删除

  // 需要先修改ProductType.java类

  // @OneToMany(mappedBy = "type",cascade=CascadeType.REMOVE)

  @Test

  public void remove() throws Exception {

    entityManager = entityManagerFactory.createEntityManager();

    entityManager.getTransaction().begin();

    ProductType type = entityManager.find(ProductType.class, 1L);

    entityManager.remove(type);

    entityManager.getTransaction().commit();

  }

  // 只删除一方，不能删除一方里面的多方

  // 需要先修改ProductType.java类

  // @OneToMany(mappedBy = "type")

  @Test

  public void remove2() throws Exception {

    entityManager = entityManagerFactory.createEntityManager();

    entityManager.getTransaction().begin();

    ProductType type = entityManager.find(ProductType.class, 1L);

    String jpql = "update Product set type=null where type=?";

    Query query = entityManager.createQuery(jpql);

    query.setParameter(1, type);

    int update = query.executeUpdate();

    System.out.println("修改成功多少条："+update);

    jpql = "delete from ProductType where id=?";

    query = entityManager.createQuery(jpql);

    query.setParameter(1, type.getId());

    update = query.executeUpdate();

    System.out.println("删除成功多少条："+update);

    entityManager.getTransaction().commit();

  }

  // 获取多方，然后删除一条多方

  @Test

  public void remove3() throws Exception {

    entityManager = entityManagerFactory.createEntityManager();

    entityManager.getTransaction().begin();

    Product product = entityManager.find(Product.class, 1L);

    entityManager.remove(product);

    entityManager.getTransaction().commit();

  }

  // 获取一方，通过一方来删除一条多方

//需要先修改ProductType.java类

  // @OneToMany(mappedBy = "type", orphanRemoval = true)

  @Test

  public void remove4() throws Exception {

    entityManager = entityManagerFactory.createEntityManager();

    entityManager.getTransaction().begin();

    Product product = entityManager.find(Product.class, 1L);

    ProductType type = entityManager.find(ProductType.class, 1L);

    type.getProducts().remove(product);

    entityManager.getTransaction().commit();

  }

  @Test

  public void find() throws Exception {

    // 不能通过一方获取多方集合是否为null，来判断是否一方是否有多方的数据，只能通过一方获取多方集合.size()来判断

    ProductType type = entityManager.find(ProductType.class, 1L);

    System.out.println(type);

    Set<Product> products = type.getProducts();

    if (products.size() > 0) {

      System.out.println("当前商品类型下面有商品的");

    } else {

      System.out.println("当前商品类型下面没有商品的");

    }

  }

  @After

  public void tearDown() throws Exception {

    if (entityManager != null && entityManager.isOpen())

      entityManager.close();

  }

  @AfterClass

  public static void tearDownAfterClass() throws Exception {

    if (entityManagerFactory != null && entityManagerFactory.isOpen())

      entityManagerFactory.close();

  }

}

其他关联项目

源码地址

https://github.com/je-ge/jpa

如果觉得我的文章对您有帮助,请打赏支持。您的支持将鼓励我继续创作!谢谢！

JPA 系列教程5-双向一对多

JPA 系列教程5-双向一对多

相关文章