Mybatis学习笔记--（三）使用注解

本文为how2java Mybatis教程的学习笔记，原教程链接如下：http://how2j.cn/k/mybatis/mybatis-tutorial/1087.html#nowhere

通过注解方式实现CRUD

创建Mapper接口

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

package com.how2java.mapper;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

在mybatis-config.xml中增加对CategoryMapper映射，原来的XML映射可以保留。

• 注解mapper标签属性名为class，xml映射文件mapper标签属性名为resource。

<mappers>    <mapper resource="com/how2java/pojo/Category.xml"/>    <mapper class="com.how2java.mapper.CategoryMapper"/>     ... </mappers>

测试

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);        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());        }    }

通过CategoryMapper mapper = session.getMapper(CategoryMapper.class);创建mapper对象，然后通过mapper对应的增删改查方法执行增删改查操作。

一对多

数据库中Category与Product之间一对多的关系通过product_表的cid字段来表示。现在要实现的功能是如何通过数据库的表结构，来填充Category实体类中products集合。

List<Product> products;

修改CategoryMapper

package com.how2java.mapper; public interface CategoryMapper {    @Select(" select * from category_ ")    @Results({          @Result(property = "id", column = "id"),        @Result(javaType = List.class,         column = "id",         many = @Many(select =             "com.how2java.mapper.ProductMapper.listByCategory"))         })    public List<Category> list();}

@Results 通过@Result和@Many中调用ProductMapper.listByCategory()方法相结合，来获取一对多关系。property属性代表的是实体类Category的属性（“id”和“products”），column属性代表的是数据库中列名（“id”）。

新增ProductMapper

package com.how2java.mapper;public interface ProductMapper {    @Select(" select * from product_ where cid = #{cid}")    public List<Product> listByCategory(int cid);}

修改mybatis-config.xml

添加ProductMapper映射。

<mappers>    <mapper resource="com/how2java/pojo/Category.xml"/>    <mapper class="com.how2java.mapper.CategoryMapper"/>      <mapper class="com.how2java.mapper.ProductMapper"/>  </mappers>

测试

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());        }    }}

运行结果：

多对一

数据库中Product与Category之间多对一的关系通过product_表的cid字段来表示。现在要实现的功能是如何通过数据库的表结构，来填充Product实体类中的category字段（数据库中存储的是int类型的id，实体类中是Category类型，因而不能直接导入）。

private Category category;

修改CategoryMapper

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

修改ProductMapper

package com.how2java.mapper;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

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());        }    }}

运行结果：

多对多

多对多是多对一和一对多的结合：对OrderItem和Product之间建立多对一关系，对Order和OrderItem建立一对多关系。即可建立Product和Order之间多对多的关系。

修改ProductMapper

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

新增OrderItemMapper

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

package com.how2java.mapper;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);}

新增OrderMapper

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

package com.how2java.mapper;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();}

修改mybatis-config.xml

<mappers>    ...    <mapper class="com.how2java.mapper.OrderItemMapper"/>    <mapper class="com.how2java.mapper.OrderMapper"/>    ...</mappers>

测试

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());            }                       }    }}

运行结果：

补充

注意：由于未建立OrderItem和Order的多对一关系，因而此时OrderItem中只填充了Product而没有填充Order。

上面从Order的角度获得和Product多对多的关系，要想从Product角度获得和Order多对多的关系，则要建立Product和OrderItem之间一对多的关系、OrderItem和Order之间多对一的关系。

Product实体类添加：

List<OrderItem> orderItems;

ProductMapper映射类添加：

@Select("select * from product_")@Results({        @Result(property = "id", column = "id"),        @Result(property = "orderItems",         javaType = List.class,         column = "id",        many = @Many(select =             "com.how2java.mapper.OrderItemMapper.listByProduct"))})public List<Product> list();

OrderItemMapper映射类添加：

@Select(" select * from order_item_ where pid = #{pid}")@Results({        @Result(property="order",column="oid",        one=@One(select="com.how2java.mapper.OrderMapper.get"))})public List<OrderItem> listByProduct(int pid);

OrderMapper映射类添加：

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

测试代码：

ProductMapper mapper1 =session.getMapper(ProductMapper.class);List<Product> ps = mapper1.list();for (Product p : ps) {    System.out.println(p.getName());    List<OrderItem> pis= p.getOrderItems();    if(null!=pis){        for (OrderItem oi : pis) {            if(oi.getOrder()!=null){                System.out.println("\t" + oi.getOrder().getCode());            }        }    }}

运行结果：

动态SQL

待补充