笔记54 Mybatis快速入门（五）

Mybatis中注解的使用

1.XML方式的CRUD

新增加接口CategoryMapper ，并在接口中声明的方法上，加上注解对比配置文件Category.xml，其实就是把SQL语句从XML挪到了注解上来。

CategoryMapper.java

 package mybatis.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 mybatis.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();
 }

在mybatis-config.xml中增加映射：

 <mapper class="mybatis.mapper.CategoryMapper"/>

测试：

 package mybatis.annotation;

 import java.io.IOException;
 import java.io.InputStream;
 import java.util.List;

 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;

 import mybatis.mapper.CategoryMapper;
 import mybatis.pojo.Category;

 public class testCRUD {
     public static void main(String[] args) throws IOException {
         String resource = "mybatis-config.xml";
         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
         SqlSession session = sqlSessionFactory.openSession();
         CategoryMapper categoryMapper = session.getMapper(CategoryMapper.class);
         add(categoryMapper);
         // listAll(categoryMapper);
         session.commit();
         session.close();

     }

     private static void update(CategoryMapper mapper) {
         Category category = mapper.get(0);
         category.setName("修改了的Category名称");
         mapper.update(category);
         listAll(mapper);
     }

     private static void delete(CategoryMapper mapper) {
         mapper.delete(2);
         listAll(mapper);
     }

     private static void add(CategoryMapper mapper) {
         Category category = new Category();
         category.setName("新增的Category");
         mapper.add(category);
         listAll(mapper);
     }

     private static void get(CategoryMapper mapper) {
         Category category = mapper.get(1);
         System.out.println(category.getName());
     }

     private static void listAll(CategoryMapper mapper) {
         List<Category> cs = mapper.list();
         for (Category c : cs) {
             System.out.println(c.getName());
         }
     }
 }

2.一对多

①查询所有Category,通过@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。

     @Select("select * from category")
     @Results({ @Result(property = "id", column = "id"),
                @Result(property = "products", javaType = List.class, column = "id", many = @Many(select = "mybatis.mapper.ProductMapper.listByCategory")) })
     public List<Category> list2();

②新增接口ProductMapper
注解@Select用于根据分类id获取产品集合
@Select(" select * from product_ where cid = #{cid}")

 package mybatis.mapper;

 import java.util.List;

 import org.apache.ibatis.annotations.Select;

 import mybatis.pojo.Product;

 public interface ProductMapper {
     @Select("select * from product where cid=#{cid}")
     public List<Product> listByCategory(int cid);
 }

③添加ProductMapper和CategoryMapper的映射

 <mapper class="mybatis.mapper.CategoryMapper"/>
 <mapper class="mybatis.mapper.ProductMapper"/>

④结果：

3.多对一

①在CategoryMapper接口中提供get方法

     @Select("select * from category where id= #{id}")
     public Category get(int id);

②在ProductMapper接口中提供list方法

 @Select("select * from product")
     @Results({ @Result(property = "id", column = "id"), @Result(property = "name", column = "name"),
             @Result(property = "price", column = "price"),
             @Result(property = "category", column = "cid", one = @One(select = "mybatis.mapper.CategoryMapper.get")) })
     public List<Product> list();

③测试

 package mybatis.annotation;

 import java.io.IOException;
 import java.io.InputStream;
 import java.util.List;

 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;

 import mybatis.mapper.ProductMapper;
 import mybatis.pojo.Product;

 public class testManyToOne {

     public static void main(String[] args) throws IOException {
         // TODO Auto-generated method stub
         String resource = "mybatis-config.xml";
         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
         SqlSession session = sqlSessionFactory.openSession();
         ProductMapper productMapper = session.getMapper(ProductMapper.class);

         List<Product> products = productMapper.list();
         for (Product product : products) {
             System.out.println(product + "\t对应的分类是：\t" + product.getCategory().getName());
         }

         session.commit();
         session.close();
     }

 }

4.多对多

①ProductMapper接口中，新增get方法。

     @Select("select * from product where id=#{id}")
     public Product get(int id);

②新增OrderItemMapper，提供listByOrder方法。
这里会与Product建立多对一关系，一种商品可以出现在多个订单中。

 package mybatis.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 mybatis.pojo.OrderItem;

 public interface OrderItemMapper {
     @Select("select * from order_item where oid=#{oid}")
     @Results({ @Result(property = "id", column = "id"), @Result(property = "number", column = "number"),
             @Result(property = "product", column = "pid", one = @One(select = "mybatis.mapper.ProductMapper.get")) })
     public List<OrderItem> listByOrder(int oid);
 }

③新增OrderMapper，提供list方法，这里会与OrderItem建立一对多关系，一个订单中会有多个商品

 package mybatis.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 mybatis.pojo.Order;

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

④修改mybatis-config.xml，增加新的映射。

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

⑤测试

 package mybatis.annotation;

 import java.io.IOException;
 import java.io.InputStream;
 import java.util.List;

 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;

 import mybatis.mapper.OrderMapper;
 import mybatis.pojo.Order;
 import mybatis.pojo.OrderItem;

 public class testManyToMany {

     public static void main(String[] args) throws IOException {
         // TODO Auto-generated method stub
         String resource = "mybatis-config.xml";
         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
         SqlSession session = sqlSessionFactory.openSession();
         OrderMapper orderMapper = session.getMapper(OrderMapper.class);
         listOrder(orderMapper);
         session.commit();
         session.close();
     }

     private static void listOrder(OrderMapper orderMapper) {
         List<Order> orders = orderMapper.list();
         for (Order order : orders) {
             System.out.println(order.getCode());
             List<OrderItem> orderItems = order.getOrderItems();
             for (OrderItem orderItem : orderItems) {
                 System.out.format("\t%s\t%f\t%d%n", orderItem.getProduct().getName(), orderItem.getProduct().getPrice(),
                         orderItem.getNumber());
             }
         }
     }

 }

5.动态SQL语句

把手写SQL语句的注解CRUD（1），修改为动态SQL语句方式。

①新增CategoryDynaSqlProvider，提供CRUD对应的SQL语句。这里的SQL语句使用SQL类的方式构建。

 package mybatis.dynasql;

 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();
     }
 }

②新增CategoryMapperDynaSQL.java

把本来是手写SQL的CategoryMapper接口，修改为注解引用CategoryDynaSqlProvider类的方式。
例如：增加本来是手写SQL语句的

     @Insert("insert into category (name) values (#{name})")
     public int add(Category category);

修改为了注解@InsertProvider配合CategoryDynaSqlProvider的add方法：

 @InsertProvider(type = CategoryMapperDynaSQL.class, method = "add")
 public int add(Category category);

 package mybatis.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 mybatis.pojo.Category;

 public interface CategoryMapperDynaSQL {
     @InsertProvider(type = CategoryMapperDynaSQL.class, method = "add")
     public int add(Category category);

     @DeleteProvider(type = CategoryMapperDynaSQL.class, method = "delete")
     public void delete(int id);

     @SelectProvider(type = CategoryMapperDynaSQL.class, method = "get")
     public Category get(int id);

     @UpdateProvider(type = CategoryMapperDynaSQL.class, method = "update")
     public int update(Category category);

     @SelectProvider(type = CategoryMapperDynaSQL.class, method = "list")
     public List<Category> list();

 }

③测试

 package mybatis.annotation;

 import java.io.IOException;
 import java.io.InputStream;
 import java.util.List;

 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;

 import mybatis.mapper.CategoryMapperDynaSQL;
 import mybatis.pojo.Category;

 public class testCRUDDynaSQL {
     public static void main(String[] args) throws IOException {
         String resource = "mybatis-config.xml";
         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
         SqlSession session = sqlSessionFactory.openSession();
         CategoryMapperDynaSQL categoryMapper = session.getMapper(CategoryMapperDynaSQL.class);
         // add(categoryMapper);
         // get(categoryMapper);
         listAll(categoryMapper);
         session.commit();
         session.close();

     }

     private static void update(CategoryMapperDynaSQL mapper) {
         Category category = mapper.get(0);
         category.setName("修改了的Category名称");
         mapper.update(category);
         listAll(mapper);
     }

     private static void delete(CategoryMapperDynaSQL mapper) {
         mapper.delete(2);
         listAll(mapper);
     }

     private static void add(CategoryMapperDynaSQL mapper) {
         Category category = new Category();
         category.setName("新增的Category");
         mapper.add(category);
         listAll(mapper);
     }

     private static void get(CategoryMapperDynaSQL mapper) {
         Category category = mapper.get(1);
         System.out.println(category.getName());
     }

     private static void listAll(CategoryMapperDynaSQL mapper) {
         List<Category> cs = mapper.list();
         for (Category c : cs) {
             System.out.println(c.getName());
         }
     }
 }