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

 1 package mybatis.mapper;
 2 
 3 import java.util.List;
 4 
 5 import org.apache.ibatis.annotations.Delete;
 6 import org.apache.ibatis.annotations.Insert;
 7 import org.apache.ibatis.annotations.Select;
 8 import org.apache.ibatis.annotations.Update;
 9 
10 import mybatis.pojo.Category;
11 
12 public interface CategoryMapper {
13     @Insert("insert into category (name) values (#{name})")
14     public int add(Category category);
15 
16     @Delete("delete from category where id= #{id}")
17     public void delete(int id);
18 
19     @Select("select * from category where id= #{id}")
20     public Category get(int id);
21 
22     @Update("update category set name=#{name} where id=#{id}")
23     public int update(Category category);
24 
25     @Select("select * from category")
26     public List<Category> list();
27 }

在mybatis-config.xml中增加映射：

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

测试：

 1 package mybatis.annotation;
 2 
 3 import java.io.IOException;
 4 import java.io.InputStream;
 5 import java.util.List;
 6 
 7 import org.apache.ibatis.session.SqlSession;
 8 import org.apache.ibatis.session.SqlSessionFactory;
 9 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
10 
11 import mybatis.mapper.CategoryMapper;
12 import mybatis.pojo.Category;
13 
14 public class testCRUD {
15     public static void main(String[] args) throws IOException {
16         String resource = "mybatis-config.xml";
17         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
18         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
19         SqlSession session = sqlSessionFactory.openSession();
20         CategoryMapper categoryMapper = session.getMapper(CategoryMapper.class);
21         add(categoryMapper);
22         // listAll(categoryMapper);
23         session.commit();
24         session.close();
25 
26     }
27 
28     private static void update(CategoryMapper mapper) {
29         Category category = mapper.get(0);
30         category.setName("修改了的Category名称");
31         mapper.update(category);
32         listAll(mapper);
33     }
34 
35     private static void delete(CategoryMapper mapper) {
36         mapper.delete(2);
37         listAll(mapper);
38     }
39 
40     private static void add(CategoryMapper mapper) {
41         Category category = new Category();
42         category.setName("新增的Category");
43         mapper.add(category);
44         listAll(mapper);
45     }
46 
47     private static void get(CategoryMapper mapper) {
48         Category category = mapper.get(1);
49         System.out.println(category.getName());
50     }
51 
52     private static void listAll(CategoryMapper mapper) {
53         List<Category> cs = mapper.list();
54         for (Category c : cs) {
55             System.out.println(c.getName());
56         }
57     }
58 }

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。

1     @Select("select * from category")
2     @Results({ @Result(property = "id", column = "id"),
3                @Result(property = "products", javaType = List.class, column = "id", many = @Many(select = "mybatis.mapper.ProductMapper.listByCategory")) })
4     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}")

 1 package mybatis.mapper;
 2 
 3 import java.util.List;
 4 
 5 import org.apache.ibatis.annotations.Select;
 6 
 7 import mybatis.pojo.Product;
 8 
 9 public interface ProductMapper {
10     @Select("select * from product where cid=#{cid}")
11     public List<Product> listByCategory(int cid);
12 }

③添加ProductMapper和CategoryMapper的映射

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

④结果：

3.多对一

①在CategoryMapper接口中提供get方法

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

②在ProductMapper接口中提供list方法

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

③测试

 1 package mybatis.annotation;
 2 
 3 import java.io.IOException;
 4 import java.io.InputStream;
 5 import java.util.List;
 6 
 7 import org.apache.ibatis.session.SqlSession;
 8 import org.apache.ibatis.session.SqlSessionFactory;
 9 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
10 
11 import mybatis.mapper.ProductMapper;
12 import mybatis.pojo.Product;
13 
14 public class testManyToOne {
15 
16     public static void main(String[] args) throws IOException {
17         // TODO Auto-generated method stub
18         String resource = "mybatis-config.xml";
19         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
20         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
21         SqlSession session = sqlSessionFactory.openSession();
22         ProductMapper productMapper = session.getMapper(ProductMapper.class);
23 
24         List<Product> products = productMapper.list();
25         for (Product product : products) {
26             System.out.println(product + "	对应的分类是：	" + product.getCategory().getName());
27         }
28 
29         session.commit();
30         session.close();
31     }
32 
33 }

4.多对多

①ProductMapper接口中，新增get方法。

1     @Select("select * from product where id=#{id}")
2     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。

 1 package mybatis.mapper;
 2 
 3 import java.util.List;
 4 
 5 import org.apache.ibatis.annotations.One;
 6 import org.apache.ibatis.annotations.Result;
 7 import org.apache.ibatis.annotations.Results;
 8 import org.apache.ibatis.annotations.Select;
 9 
10 import mybatis.pojo.OrderItem;
11 
12 public interface OrderItemMapper {
13     @Select("select * from order_item where oid=#{oid}")
14     @Results({ @Result(property = "id", column = "id"), @Result(property = "number", column = "number"),
15             @Result(property = "product", column = "pid", one = @One(select = "mybatis.mapper.ProductMapper.get")) })
16     public List<OrderItem> listByOrder(int oid);
17 }

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

 1 package mybatis.mapper;
 2 
 3 import java.util.List;
 4 
 5 import org.apache.ibatis.annotations.Many;
 6 import org.apache.ibatis.annotations.Result;
 7 import org.apache.ibatis.annotations.Results;
 8 import org.apache.ibatis.annotations.Select;
 9 
10 import mybatis.pojo.Order;
11 
12 public interface OrderMapper {
13     @Select("select * from order_")
14     @Results({ @Result(property = "id", column = "id"), @Result(property = "code", column = "code"),
15             @Result(property = "orderItems", column = "id", javaType = List.class, many = @Many(select = "mybatis.mapper.OrderItemMapper.listByOrder")) })
16     public List<Order> list();
17 }

④修改mybatis-config.xml，增加新的映射。

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

⑤测试

 1 package mybatis.annotation;
 2 
 3 import java.io.IOException;
 4 import java.io.InputStream;
 5 import java.util.List;
 6 
 7 import org.apache.ibatis.session.SqlSession;
 8 import org.apache.ibatis.session.SqlSessionFactory;
 9 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
10 
11 import mybatis.mapper.OrderMapper;
12 import mybatis.pojo.Order;
13 import mybatis.pojo.OrderItem;
14 
15 public class testManyToMany {
16 
17     public static void main(String[] args) throws IOException {
18         // TODO Auto-generated method stub
19         String resource = "mybatis-config.xml";
20         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
21         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
22         SqlSession session = sqlSessionFactory.openSession();
23         OrderMapper orderMapper = session.getMapper(OrderMapper.class);
24         listOrder(orderMapper);
25         session.commit();
26         session.close();
27     }
28 
29     private static void listOrder(OrderMapper orderMapper) {
30         List<Order> orders = orderMapper.list();
31         for (Order order : orders) {
32             System.out.println(order.getCode());
33             List<OrderItem> orderItems = order.getOrderItems();
34             for (OrderItem orderItem : orderItems) {
35                 System.out.format("	%s	%f	%d%n", orderItem.getProduct().getName(), orderItem.getProduct().getPrice(),
36                         orderItem.getNumber());
37             }
38         }
39     }
40 
41 }

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。

 1 package mybatis.dynasql;
 2 
 3 import org.apache.ibatis.jdbc.SQL;
 4 
 5 public class CategoryDynaSqlProvider {
 6     public String list() {
 7         return new SQL().SELECT("*").FROM("category").toString();
 8     }
 9 
10     public String get() {
11         return new SQL().SELECT("*").FROM("category").WHERE("id=#{id}").toString();
12     }
13 
14     public String add() {
15         return new SQL().INSERT_INTO("category").VALUES("name", "#{name}").toString();
16     }
17 
18     public String update() {
19         return new SQL().UPDATE("category").SET("name=#{name}").WHERE("id=#{id}").toString();
20     }
21 
22     public String delete() {
23         return new SQL().DELETE_FROM("category").WHERE("id=#{id}").toString();
24     }
25 }

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

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

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

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

 1 package mybatis.mapper;
 2 
 3 import java.util.List;
 4 
 5 import org.apache.ibatis.annotations.DeleteProvider;
 6 import org.apache.ibatis.annotations.InsertProvider;
 7 import org.apache.ibatis.annotations.SelectProvider;
 8 import org.apache.ibatis.annotations.UpdateProvider;
 9 
10 import mybatis.pojo.Category;
11 
12 public interface CategoryMapperDynaSQL {
13     @InsertProvider(type = CategoryMapperDynaSQL.class, method = "add")
14     public int add(Category category);
15 
16     @DeleteProvider(type = CategoryMapperDynaSQL.class, method = "delete")
17     public void delete(int id);
18 
19     @SelectProvider(type = CategoryMapperDynaSQL.class, method = "get")
20     public Category get(int id);
21 
22     @UpdateProvider(type = CategoryMapperDynaSQL.class, method = "update")
23     public int update(Category category);
24 
25     @SelectProvider(type = CategoryMapperDynaSQL.class, method = "list")
26     public List<Category> list();
27 
28 }

③测试

 1 package mybatis.annotation;
 2 
 3 import java.io.IOException;
 4 import java.io.InputStream;
 5 import java.util.List;
 6 
 7 import org.apache.ibatis.session.SqlSession;
 8 import org.apache.ibatis.session.SqlSessionFactory;
 9 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
10 
11 import mybatis.mapper.CategoryMapperDynaSQL;
12 import mybatis.pojo.Category;
13 
14 public class testCRUDDynaSQL {
15     public static void main(String[] args) throws IOException {
16         String resource = "mybatis-config.xml";
17         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
18         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
19         SqlSession session = sqlSessionFactory.openSession();
20         CategoryMapperDynaSQL categoryMapper = session.getMapper(CategoryMapperDynaSQL.class);
21         // add(categoryMapper);
22         // get(categoryMapper);
23         listAll(categoryMapper);
24         session.commit();
25         session.close();
26 
27     }
28 
29     private static void update(CategoryMapperDynaSQL mapper) {
30         Category category = mapper.get(0);
31         category.setName("修改了的Category名称");
32         mapper.update(category);
33         listAll(mapper);
34     }
35 
36     private static void delete(CategoryMapperDynaSQL mapper) {
37         mapper.delete(2);
38         listAll(mapper);
39     }
40 
41     private static void add(CategoryMapperDynaSQL mapper) {
42         Category category = new Category();
43         category.setName("新增的Category");
44         mapper.add(category);
45         listAll(mapper);
46     }
47 
48     private static void get(CategoryMapperDynaSQL mapper) {
49         Category category = mapper.get(1);
50         System.out.println(category.getName());
51     }
52 
53     private static void listAll(CategoryMapperDynaSQL mapper) {
54         List<Category> cs = mapper.list();
55         for (Category c : cs) {
56             System.out.println(c.getName());
57         }
58     }
59 }

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原文地址：https://www.cnblogs.com/lyj-gyq/p/9241110.html