Hibernate注解-多对一关系映射注解，一对多关系映射注解，多对多关系映射注解

• 多对一注解
  
  把多对一改成用注解来实现
  1. 把Category的id和name字段改为支持注解
  注： 分类的getName上并没有加上@Column(name="name")，也可以达到映射的效果。 因为getName方法默认会被认为是字段映射。 除非加上了@Transient 才表示不进行映射
  2. 把Product的getCategory进行多对一映射
  

    @ManyToOne
      @JoinColumn(name="cid") 
      public Category getCategory() {
          return category;
      }

  @ManyToOne 表示多对一关系
  @JoinColumn(name="cid") 表示关系字段是cid
  对比xml中的映射方式：
  
  3. 为hibernate.cfg.xml 添加Category的映射
  
  4. 运行TestHibernate
  
  

  import javax.persistence.Column;
   
  import javax.persistence.Entity;
  import javax.persistence.GeneratedValue;
  import javax.persistence.GenerationType;
  import javax.persistence.Id;
  import javax.persistence.Table;
   
  @Entity
  @Table(name = "category_")
  public class Category {
      int id;
      String name;
       
      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      @Column(name = "id")
      public int getId() {
          return id;
      }
      public void setId(int id) {
          this.id = id;
      }
       
      public String getName() {
          return name;
      }
      public void setName(String name) {
          this.name = name;
      }
   
  }

  import javax.persistence.CascadeType;
  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.GeneratedValue;
  import javax.persistence.GenerationType;
  import javax.persistence.Id;
  import javax.persistence.JoinColumn;
  import javax.persistence.ManyToOne;
  import javax.persistence.Table;
    
  @Entity
  @Table(name = "product_")
  public class Product {
      int id;
      String name;
      float price;
       
      Category category;
   
      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      @Column(name = "id")  
      public int getId() {
          return id;
      }
      public void setId(int id) {
          this.id = id;
      }
      @Column(name = "name")
      public String getName() {
          return name;
      }
      public void setName(String name) {
          this.name = name;
      }
      @Column(name = "price")
      public float getPrice() {
          return price;
      }
      public void setPrice(float price) {
          this.price = price;
      }
   
      @ManyToOne
      @JoinColumn(name="cid")
      public Category getCategory() {
          return category;
      }
      public void setCategory(Category category) {
          this.category = category;
      }
  }

  
  
     
  
     
      
          
          com.mysql.jdbc.Driver
          jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8
          utf-8
          root
          admin
          
          org.hibernate.dialect.MySQLDialect
          thread
          true
          update
  
          
          
    
      
     
  

• 一对多注解
  
  在上一步的基础上做如下改动
  1. 为Category再加product集合，并提供getter和setter
  

  Set products;
      public Set getProducts() {
          return products;
      }
      public void setProducts(Set products) {
          this.products = products;
      }

  2. 给getProducts方法加上一对多注解
  

  @OneToMany(fetch=FetchType.EAGER)
      @JoinColumn(name="cid") 
      public Set getProducts() {
          return products;
      }

  @OneToMany 表示一对多,fetch=FetchType.EAGER 表示不进行延迟加载(FetchType.LAZY表示要进行延迟加载)
  @JoinColumn(name="cid") 表示映射字段
  对比xml中的映射方式：
  
  3. 修改TestHibernate为
  

    SessionFactory sf = new Configuration().configure().buildSessionFactory();
          Session s = sf.openSession();
          s.beginTransaction();
          Category c = (Category) s.get(Category.class, 1);
          s.getTransaction().commit();
          s.close();
          sf.close();
          Set ps = c.getProducts();
          for (Product p : ps) {
              System.out.println(p.getName());
          }

  import java.util.Set;
   
  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.FetchType;
  import javax.persistence.GeneratedValue;
  import javax.persistence.GenerationType;
  import javax.persistence.Id;
  import javax.persistence.JoinColumn;
  import javax.persistence.OneToMany;
  import javax.persistence.Table;
   
  @Entity
  @Table(name = "category_")
  public class Category {
      int id;
      String name;
      Set products;
      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      @Column(name = "id")
      public int getId() {
          return id;
      }
      public void setId(int id) {
          this.id = id;
      }
       
      public String getName() {
          return name;
      }
      public void setName(String name) {
          this.name = name;
      }
       
      @OneToMany(fetch=FetchType.EAGER)
      @JoinColumn(name="cid")
      public Set getProducts() {
          return products;
      }
      public void setProducts(Set products) {
          this.products = products;
      }
  }

  import java.util.Set;
   
  import org.hibernate.Session;
  import org.hibernate.SessionFactory;
  import org.hibernate.cfg.Configuration;
   
  import com.how2java.pojo.Category;
  import com.how2java.pojo.Product;
    
  public class TestHibernate {
      public static void main(String[] args) {
          SessionFactory sf = new Configuration().configure().buildSessionFactory();
          Session s = sf.openSession();
          s.beginTransaction();
          Category c = (Category) s.get(Category.class, 1);
          s.getTransaction().commit();
          s.close();
          sf.close();
          Set ps = c.getProducts();
          for (Product p : ps) {
              System.out.println(p.getName());
          }
      }
  }

• 多对多注解
  
  1. 在基于XML配置的多对多知识点的基础上进行多对多注解的修改
  2.像上两步那样，为Product,User,Category 加上类和属性注解
  3. 加上多对一注解ManyToOne
  4. 加上一对多注解OneToMany
  
  5. ManyToMany
  为Product的getUsers加上
  

   @ManyToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
      @JoinTable(
              name="user_product",
              joinColumns=@JoinColumn(name="pid"),
              inverseJoinColumns=@JoinColumn(name="uid")
      )    
      public Set getUsers() {
          return users;
      }

  对比Product.hbm.xml中的配置：
  
  
  
  为User的getProducts加上
  

    @ManyToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
      @JoinTable(
              name="user_product",
              joinColumns=@JoinColumn(name="uid"),
              inverseJoinColumns=@JoinColumn(name="pid")
      )    
      public Set getProducts() {
          return products;
      }

  对比User.hbm.xml中的配置
  
  
  6. hibernate.cfg.xml
  
  7. 运行TestHibernate
  

  import java.util.Set;
   
  import javax.persistence.CascadeType;
  import javax.persistence.Entity;
  import javax.persistence.FetchType;
  import javax.persistence.GeneratedValue;
  import javax.persistence.GenerationType;
  import javax.persistence.Id;
  import javax.persistence.JoinColumn;
  import javax.persistence.JoinTable;
  import javax.persistence.ManyToMany;
  import javax.persistence.Table;
    
  @Entity
  @Table(name="user_")
  public class User {
    
      int id;
      String name;
      Set products;
      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      public int getId() {
          return id;
      }
      public void setId(int id) {
          this.id = id;
      }
      public String getName() {
          return name;
      }
      public void setName(String name) {
          this.name = name;
      }
      @ManyToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
      @JoinTable(
              name="user_product",
              joinColumns=@JoinColumn(name="uid"),
              inverseJoinColumns=@JoinColumn(name="pid")
      )   
      public Set getProducts() {
          return products;
      }
      public void setProducts(Set products) {
          this.products = products;
      }
  }

  import java.util.Set;
   
  import javax.persistence.CascadeType;
  import javax.persistence.Entity;
  import javax.persistence.FetchType;
  import javax.persistence.GeneratedValue;
  import javax.persistence.GenerationType;
  import javax.persistence.Id;
  import javax.persistence.JoinColumn;
  import javax.persistence.JoinTable;
  import javax.persistence.ManyToMany;
  import javax.persistence.ManyToOne;
  import javax.persistence.Table;
    
  @Entity
  @Table(name="product_")
  public class Product {
      int id;
      String name;
      float price;
      Category category;
      Set users;
    
      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      public int getId() {
          return id;
      }
      public void setId(int id) {
          this.id = id;
      }
       
      @ManyToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
      @JoinTable(
              name="user_product",
              joinColumns=@JoinColumn(name="pid"),
              inverseJoinColumns=@JoinColumn(name="uid")
      )   
      public Set getUsers() {
          return users;
      }
      public void setUsers(Set users) {
          this.users = users;
      }
       
      @ManyToOne
      @JoinColumn(name="cid")    
      public Category getCategory() {
          return category;
      }
      public void setCategory(Category category) {
          this.category = category;
      }
       
      public String getName() {
          return name;
      }
      public void setName(String name) {
          this.name = name;
      }
      public float getPrice() {
          return price;
      }
      public void setPrice(float price) {
          this.price = price;
      }
        
  }

  import java.util.Set;
   
  import javax.persistence.Entity;
  import javax.persistence.FetchType;
  import javax.persistence.GeneratedValue;
  import javax.persistence.GenerationType;
  import javax.persistence.Id;
  import javax.persistence.JoinColumn;
  import javax.persistence.OneToMany;
  import javax.persistence.Table;
    
  @Entity
  @Table(name="category_")
  public class Category {
      int id;
      String name;
      Set products;
       
      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      public int getId() {
          return id;
      }
      public void setId(int id) {
          this.id = id;
      }
      public String getName() {
          return name;
      }
      public void setName(String name) {
          this.name = name;
      }
   
      @OneToMany(fetch=FetchType.EAGER)
      @JoinColumn(name="cid")    
      public Set getProducts() {
          return products;
      }
      public void setProducts(Set products) {
          this.products = products;
      }
  }

  import java.util.HashSet;
  import java.util.Set;
    
  import org.hibernate.Session;
  import org.hibernate.SessionFactory;
  import org.hibernate.cfg.Configuration;
    
  import com.how2java.pojo.Product;
  import com.how2java.pojo.User;
     
  public class TestHibernate {
      public static void main(String[] args) {
          SessionFactory sf = new Configuration().configure().buildSessionFactory();
     
          Session s = sf.openSession();
          s.beginTransaction();
            
  //        //增加3个用户
          Set users = new HashSet();
          for (int i = 0; i < 3; i++) {
              User u =new User();
              u.setName("user"+i);
              users.add(u);
              s.save(u);
          }
            
          //产品1被用户1,2,3购买
          Product p1 = (Product) s.get(Product.class, 1);
   
          p1.setUsers(users);
          s.getTransaction().commit();
          s.close();
          sf.close();
      }
  }

  
  
    
  
    
      
          
          com.mysql.jdbc.Driver
          jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8
          utf-8
          root
          admin
          
          org.hibernate.dialect.MySQLDialect
          thread
          true
          update