• 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

    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.class1);

    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.class1);

            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.class1);

            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
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