MyBatis框架注解（四）

MyBatis注解

注解与实体xml配置文件有着同样的作用，它们有着各自的优势。

XML配置方式：

优：容易编辑，配置比较集中，方便修改，在大业务量的系统里面，通过xml配置会方便后人理解整个系统的架构，修改之后直接重启应用即可

缺：比较繁琐，配置形态丑陋, 配置文件过多的时候难以管理

注解方式：

优：方便，简洁，配置信息和 Java 代码放在一起，有助于增强程序的内聚性。

缺：分散到各个class文件中，所以不宜维护, 修改之后你需要重新打包，发布，重启应用。

CRUD注解

本例把MyBatis框架入门（一）XML方式的CRUD修改为注解方式

删除Category.xml，创建CategoryMapper接口

package mapper;
  
import java.util.List;
 
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;
 
import pojo.Category;
  
public interface CategoryMapper {
  
    @Insert(" insert into category ( name ) values (#{name}) ")  
    public int add(Category category);  
        
    @Delete(" delete from category where id= #{id} ")  
    public void delete(int id);  
        
    @Select("select * from category where id= #{id} ")  
    public Category get(int id);  
      
    @Update("update category set name=#{name} where id=#{id} ")  
    public int update(Category category);   
        
    @Select(" select * from category_ ")  
    public List<Category> list();  
}

修改mybatis-config.xml配置文件

只需添加这句映射

<mapper class="mapper.CategoryMapper"/>

在主类编写运行逻辑

public class App {
   
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        CategoryMapper mapper = session.getMapper(CategoryMapper.class);
  
        add(mapper);
        delete(mapper);
        get(mapper);
        update(mapper);
        listAll(mapper);
              
        session.commit();
        session.close();
   
    }
  
    private static void update(CategoryMapper mapper) {
        Category c= mapper.get(8);
        c.setName("修改了的Category名稱");
        mapper.update(c);
        listAll(mapper);
    }
  
    private static void get(CategoryMapper mapper) {
        Category c= mapper.get(8);
        System.out.println(c.getName());
    }
  
    private static void delete(CategoryMapper mapper) {
        mapper.delete(2);
        listAll(mapper);
    }
  
    private static void add(CategoryMapper mapper) {
        Category c = new Category();
        c.setName("新增加的Category");
        mapper.add(c);
        listAll(mapper);
    }
   
    private static void listAll(CategoryMapper mapper) {
        List<Category> cs = mapper.list();
        for (Category c : cs) {
            System.out.println(c.getName());
        }
    }
}

一对多注解

本例把MyBatis框架进阶（二）XML方式的一对多修改为注解方式

修改CategoryMapper接口

@Select注解获取Category类本身

@Results 通过@Result和@Many中调用ProductMapper.listByCategory()方法相结合，来获取一对多关系

package mapper;
 
import java.util.List;
 
import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
 
import pojo.Category;
 
public interface CategoryMapper {
    @Select(" select * from category ")
    @Results({  
                @Result(property = "id", column = "id"),
                @Result(property = "products", javaType = List.class, column = "id", many = @Many(select = "mapper.ProductMapper.listByCategory") ) 
            })
    public List<Category> list();
 
}

创建ProductMapper接口

注解@Select用于根据分类id获取产品集合

package mapper;
  
import java.util.List;
 
import org.apache.ibatis.annotations.Select;
 
import pojo.Product;
  
public interface ProductMapper {
  
    @Select(" select * from product where cid = #{cid}")
    public List<Product> listByCategory(int cid);
     
}

修改mybatis-config.xml配置文件

添加ProductMapper映射

<mapper class="mapper.ProductMapper"/>

在主类中编写运行逻辑

public class App {
   
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        CategoryMapper mapper = session.getMapper(CategoryMapper.class);
 
        listAll(mapper);
              
        session.commit();
        session.close();
   
    }
  
    private static void listAll(CategoryMapper mapper) {
        List<Category> cs = mapper.list();
        for (Category c : cs) {
            System.out.println(c.getName());
            List<Product> ps = c.getProducts();
            for (Product p : ps) {
                System.out.println("\t"+p.getName());
            }
        }
    }
}

多对一注解

本例把MyBatis框架进阶（二）XML方式的多对一修改为注解方式

修改CategoryMapper接口

package mapper;
  
import org.apache.ibatis.annotations.Select;
 
import pojo.Category;
  
public interface CategoryMapper {
    @Select(" select * from category where id = #{id}")
    public Category get(int id);
     
}

修改ProductMapper接口

package mapper;
  
import java.util.List;
 
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
 
import pojo.Product;
  
public interface ProductMapper {
    @Select(" select * from product ")
    @Results({  
        @Result(property="category",column="cid",one=@One(select="mapper.CategoryMapper.get"))  
    }) 
    public List<Product> list();
}

在主类中编写运行逻辑

public class App {
   
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        ProductMapper mapper = session.getMapper(ProductMapper.class);
 
        List<Product> ps= mapper.list();
        for (Product p : ps) {
            System.out.println(p + "\t对应的分类是:\t" + p.getCategory().getName());
        }
 
        session.commit();
        session.close();
   
    }
}

多对多注解

本例把MyBatis框架进阶（二）XML方式的多对多修改为注解方式

修改ProductMapper接口

package mapper;
 
import org.apache.ibatis.annotations.Select;
 
import pojo.Product;
 
public interface ProductMapper {
     
    @Select("select * from product where id = #{id}")
    public Product get(int id);
}

创建OrderItemMapper接口

新增OrderItemMapper，提供listByOrder方法。这里会与Product建立多对一关

package mapper;
 
import java.util.List;
 
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
 
import pojo.OrderItem;
 
public interface OrderItemMapper {
     
    @Select(" select * from order_item where oid = #{oid}")
    @Results({  
        @Result(property="product",column="pid",one=@One(select="com.how2java.mapper.ProductMapper.get"))  
    })  
    public List<OrderItem> listByOrder(int oid);
}

创建OrdersMapper接口

新增OrderMapper，提供list方法，这里会与OrderItem建立一对多关系

package mapper;
 
import java.util.List;
 
import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
 
import pojo.Order;
 
public interface OrdersMapper {
    @Select("select * from orders")
     @Results({
            @Result(property = "id", column = "id"),
            @Result(property = "orderItems", javaType = List.class, column = "id",  
                    many = @Many(select = "mapper.OrderItemMapper.listByOrder"))
            })       
    public List<Order> list();
     
}

修改mybatis-config.xml配置文件

添加OrdersMapper和OrderItemMapper映射

        <mapper class="mapper.OrderItemMapper"/>
        <mapper class="mapper.OrderMapper"/>

在主类中编写运行逻辑

运行测试遍历所有的订单，再通过一对多和多对一，间接地多对多遍历出产品。

public class App {
  
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
  
        listOrders(session);
 
        session.commit();
        session.close();
  
    }
 
    private static void listOrders(SqlSession session) {
        OrdersMapper mapper =session.getMapper(OrdersMapper.class);
        List<Orders> os = mapper.list();
        for (Orders o : os) {
            System.out.println(o.getCode());
            List<OrderItem> ois= o.getOrderItems();
            if(null!=ois){
                for (OrderItem oi : ois) {
                    System.out.format("\t%s\t%f\t%d%n", oi.getProduct().getName(),oi.getProduct().getPrice(),oi.getNumber());
                }               
            }
 
        }
    }
}

动态SQL注解

创建CategoryDynaSqlProvider

新增CategoryDynaSqlProvider，提供CRUD对应的SQL语句。

public class CategoryDynaSqlProvider {
    public String list() {
         return new SQL()
                 .SELECT("*")
                 .FROM("category")
                 .toString();
         
    }
    public String get() {
        return new SQL()
                .SELECT("*")
                .FROM("category")
                .WHERE("id=#{id}")
                .toString();
    }
     
    public String add(){
        return new SQL()
                .INSERT_INTO("category")
                .VALUES("name", "#{name}")
                .toString();
    }
    public String update(){
        return new SQL()
                .UPDATE("category")
                .SET("name=#{name}")
                .WHERE("id=#{id}")
                .toString();
    }
    public String delete(){
        return new SQL()
                .DELETE_FROM("category")
                .WHERE("id=#{id}")
                .toString();
    }
     
}

修改CategoryMapper接口

 public interface CategoryMapper {
  
    @InsertProvider(type=CategoryDynaSqlProvider.class,method="add")  
    public int add(Category category);  
        
    @DeleteProvider(type=CategoryDynaSqlProvider.class,method="delete")
    public void delete(int id);  
        
    @SelectProvider(type=CategoryDynaSqlProvider.class,method="get")  
    public Category get(int id);  
      
    @UpdateProvider(type=CategoryDynaSqlProvider.class,method="update")  
    public int update(Category category);   
        
    @SelectProvider(type=CategoryDynaSqlProvider.class,method="list")      
    public List<Category> list();  
}

在主类中编写运行逻辑

public class App {
   
    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        CategoryMapper mapper = session.getMapper(CategoryMapper.class);
  
        add(mapper);
        delete(mapper);
        get(mapper);
        update(mapper);
        listAll(mapper);
              
        session.commit();
        session.close();
   
    }
  
    private static void update(CategoryMapper mapper) {
        Category c= mapper.get(14);
        c.setName("修改了的Category名稱");
        mapper.update(c);
        listAll(mapper);
    }
  
    private static void get(CategoryMapper mapper) {
        Category c= mapper.get(14);
        System.out.println(c.getName());
    }
  
    private static void delete(CategoryMapper mapper) {
        mapper.delete(13);
        listAll(mapper);
    }
  
    private static void add(CategoryMapper mapper) {
        Category c = new Category();
        c.setName("新增加的Category");
        mapper.add(c);
        listAll(mapper);
    }
   
    private static void listAll(CategoryMapper mapper) {
        List<Category> cs = mapper.list();
        for (Category c : cs) {
            System.out.println(c.getName());
        }
    }
}