Hibernate系列教材 （二十八）- 注解

步骤1:先运行，看到效果，再学习
步骤2:模仿和排错
步骤3:多对一注解
步骤4:一对多注解
步骤5:多对多注解

步骤 1 : 先运行，看到效果，再学习

老规矩，先下载下载区(点击进入)的可运行项目，配置运行起来，确认可用之后，再学习做了哪些步骤以达到这样的效果。

步骤 2 : 模仿和排错

在确保可运行项目能够正确无误地运行之后，再严格照着教程的步骤，对代码模仿一遍。 
模仿过程难免代码有出入，导致无法得到期望的运行结果，此时此刻通过比较正确答案 ( 可运行项目 ) 和自己的代码，来定位问题所在。 
采用这种方式，学习有效果，排错有效率，可以较为明显地提升学习速度，跨过学习路上的各个槛。 

推荐使用diffmerge软件，进行文件夹比较。把你自己做的项目文件夹，和我的可运行项目文件夹进行比较。 
这个软件很牛逼的，可以知道文件夹里哪两个文件不对，并且很明显地标记出来 
这里提供了绿色安装和使用教程：diffmerge 下载和使用教程

步骤 3 : 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：

<many-to-one name="category" class="Category" column="cid" />


3. 为hibernate.cfg.xml 添加Category的映射

<mapping class="com.how2java.pojo.Category" />


4. 运行TestHibernate

package com.how2java.pojo;

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;

    }

}

package com.how2java.pojo;

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;

    }

}

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

       "-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

   

<hibernate-configuration>

   

    <session-factory>

        <!-- Database connection settings -->

        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>

        <property name="connection.url">jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8</property>

        <property name="connection.characterEncoding">utf-8</property>

        <property name="connection.username">root</property>

        <property name="connection.password">admin</property>

        <!-- SQL dialect -->

        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

        <property name="current_session_context_class">thread</property>

        <property name="show_sql">true</property>

        <property name="hbm2ddl.auto">update</property>

<!--    <mapping resource="com/how2java/pojo/Product.hbm.xml" /> -->

        <mapping class="com.how2java.pojo.Product" />

        <mapping class="com.how2java.pojo.Category" />

  

    </session-factory>

   

</hibernate-configuration>

步骤 4 : 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<Product> products;

public Set<Product> getProducts() {

    return products;

}

public void setProducts(Set<Product> 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<Product> 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：

<set name="products" lazy="false">

    <key column="cid" not-null="false" />

    <one-to-many class="Product" />

</set>


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<Product> ps = c.getProducts();

for (Product p : ps) {

    System.out.println(p.getName());

}

package com.how2java.pojo;

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<Product> 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<Product> getProducts() {

        return products;

    }

    public void setProducts(Set<Product> products) {

        this.products = products;

    }

}

package com.how2java.test;

   

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<Product> ps = c.getProducts();

        for (Product p : ps) {

            System.out.println(p.getName());

        }

    }

}

步骤 5 : 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<User> getUsers() {

    return users;

}


对比Product.hbm.xml中的配置：

<set name="users" table="user_product" lazy="false">

     <key column="pid" />

     <many-to-many column="uid" class="User" />

 </set>  


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<Product> getProducts() {

    return products;

}


对比User.hbm.xml中的配置

<set name="products" table="user_product" lazy="false">

    <key column="uid" />

    <many-to-many column="pid" class="Product" />

</set>   




6. hibernate.cfg.xml

<mapping class="com.how2java.pojo.Product" />

<mapping class="com.how2java.pojo.Category" />

<mapping class="com.how2java.pojo.User" />


7. 运行TestHibernate

package com.how2java.pojo;

  

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<Product> 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<Product> getProducts() {

        return products;

    }

    public void setProducts(Set<Product> products) {

        this.products = products;

    }

}

package com.how2java.pojo;

  

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<User> 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<User> getUsers() {

        return users;

    }

    public void setUsers(Set<User> 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;

    }

      

}

package com.how2java.pojo;

  

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<Product> 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<Product> getProducts() {

        return products;

    }

    public void setProducts(Set<Product> products) {

        this.products = products;

    }

}

package com.how2java.test;

   

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<User> 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();

    }

}

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

       "-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

  

<hibernate-configuration>

  

    <session-factory>

        <!-- Database connection settings -->

        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>

        <property name="connection.url">jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8</property>

        <property name="connection.characterEncoding">utf-8</property>

        <property name="connection.username">root</property>

        <property name="connection.password">admin</property>

        <!-- SQL dialect -->

        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

        <property name="current_session_context_class">thread</property>

        <property name="show_sql">true</property>

        <property name="hbm2ddl.auto">update</property>

        <mapping class="com.how2java.pojo.Product" />

        <mapping class="com.how2java.pojo.Category" />

        <mapping class="com.how2java.pojo.User" />

    </session-factory>

  

</hibernate-configuration>

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原文地址：https://www.cnblogs.com/Lanht/p/12789393.html