Mybatis学习笔记（三） 注解

和之前学习的spring一样，利用注解的方式代替映射文件。

注解CRUD

新增加一个CategoryMapper接口，并在方法的上面加上注解，对比之前的xml映射，就是把sql语句提到了注解上面。

package com.how2java.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 com.how2java.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(); 
}

并在Mybatis-config.xml中加上对CategoryMapper的映射：

<mapper class="com.how2java.mapper.CategoryMapper"/> 

然后在测试类上面，就可以直接测试我们的CRUD了

package com.how2java;
   
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.mapper.CategoryMapper;
import com.how2java.pojo.Category;
   
public class TestMybatis {
   
    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());
        }
    }
}

注解实现一对多

先新增一个接口ProductMapper接口， 作用是根据分类id来获取产品集合：

package com.how2java.mapper;
  
import java.util.List;
 
import org.apache.ibatis.annotations.Select;
 
import com.how2java.pojo.Product;
  
public interface ProductMapper {
  
    @Select(" select * from product_ where cid = #{cid}")
    public List<Product> listByCategory(int cid);
     
}

然后改一下CategoryMapper的内容，

@select是获取category类本身

@Results()是配合Result一起使用，用来封装多个结果集

@Result() 用来实现结果集的封装。里面的属性property是需要给实体装配的属性名，column是在数据库中对应的列名。这里第二条的result里面的column就是 在执行many中的select的时候，把category_表中的id作为参数穿进去，所以我们的ProductMapper中直接用的是cid而不是id。然后！默认情况下，一个column（数据库字段）只映射到 “自身”JavaBean的一个property，即属性。由于第二条里面把id映射到listByCategory里面作为参数了，就不会在映射我们本身的id了。所以我们需要加上第一条@Result来把category_表里的id映射到咱拿出来的Category实体类的id里面。 

如果不加第一条@Result的话，后边list出来的id全是0. 这是有点不好理解的地方。

@Many() 用来实现一对多的结果集的封装 就像是代替了collection标签。javaType是指定映射的java实体类的属性，这里是list。然后many里面是上面写好的ProductMapper里面的listByCategory方法。

package com.how2java.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 com.how2java.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 = "com.how2java.mapper.ProductMapper.listByCategory") )
            })
    public List<Category> list();
 
}

然后，翠花上测试类：

package com.how2java;
   
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.mapper.CategoryMapper;
import com.how2java.pojo.Category;
import com.how2java.pojo.Product;
   
public class TestMybatis {
   
    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());
            }
        }
    }
}

这就完成了一对多啦。比之前映射简单多啦。

注解多对一

改一下categoryMapper

提供一个get方法，查询一个Category

package com.how2java.mapper;
  
import org.apache.ibatis.annotations.Select;
 
import com.how2java.pojo.Category;
  
public interface CategoryMapper {
    @Select(" select * from category_ where id = #{id}")
    public Category get(int id);
     
}

改一下productmapper，提供list方法，查询一个产品集合

@result 里面 把 产品的cid传给上面的CategoryMapper的get方法。

要注意这里就不用写id对应id了，因为映射给CategoryMapper的是cid， 而product的id还是映射给自己啦。

package com.how2java.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 com.how2java.pojo.Product;
  
public interface ProductMapper {
    @Select(" select * from product_ ")
    @Results({ 
        @Result(property="category",column="cid",one=@One(select="com.how2java.mapper.CategoryMapper.get")) 
    })
    public List<Product> list();
}

 测试类：

package com.how2java;
   
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.mapper.ProductMapper;
import com.how2java.pojo.Product;
   
public class TestMybatis {
   
    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();
   
    }
}

注解多对多查询：

给product一个get方法。

package com.how2java.mapper;
 
import org.apache.ibatis.annotations.Select;
 
import com.how2java.pojo.Product;
 
public interface ProductMapper {
     
    @Select("select * from product_ where id = #{id}")
    public Product get(int id);
}

新增OrderItemMapper

提供list方法，返回OrderItem集合，并且和ProductMapper提供一个多对一的关系

package com.how2java.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 com.how2java.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);
}

然后新增一个OrderMapper

提供list方法 与orderItem建立一对多的关系：

注意这里需要映射id啦。

package com.how2java.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 com.how2java.pojo.Order;
 
public interface OrderMapper {
    @Select("select * from order_")
     @Results({
            @Result(property = "id", column = "id"),
            @Result(property = "orderItems", javaType = List.class, column = "id", 
                    many = @Many(select = "com.how2java.mapper.OrderItemMapper.listByOrder"))
            })      
    public List<Order> list();
     
}

测试类：

package com.how2java;
  
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.mapper.OrderMapper;
import com.how2java.pojo.Order;
import com.how2java.pojo.OrderItem;
import com.how2java.pojo.Product;
  
public class TestMybatis {
  
    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();
  
        listOrder(session);
 
        session.commit();
        session.close();
  
    }
 
    private static void listOrder(SqlSession session) {
        OrderMapper mapper =session.getMapper(OrderMapper.class);
        List<Order> os = mapper.list();
        for (Order 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());
                }              
            }
 
        }
    }
}

注解 动态sql

提供一个CategoryDynaSqlProvider类（不是接口），用来提供CRUD对应的sql语句

SQL类是用于进行动态sql生成的。这里都是基础的CRUD，后边复杂情况就会碰到where啊什么的。

这样就避免在java代码里写sql语句，如果想维护sql语句，不用动java代码。

package com.how2java;
 
import org.apache.ibatis.jdbc.SQL;
 
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();
    }
     
}

修改一下CategoryMapper类，配合一下CategoryDynaSqlProvider的方法：

package com.how2java.mapper;
  
import java.util.List;
 
import org.apache.ibatis.annotations.DeleteProvider;
import org.apache.ibatis.annotations.InsertProvider;
import org.apache.ibatis.annotations.SelectProvider;
import org.apache.ibatis.annotations.UpdateProvider;
 
import com.how2java.CategoryDynaSqlProvider;
import com.how2java.pojo.Category;
  
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(); 
}

测试类：

package com.how2java;
   
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
 
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import com.how2java.mapper.CategoryMapper;
import com.how2java.pojo.Category;
   
public class TestMybatis {
   
    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());
        }
    }
}

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