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笔记52 Mybatis快速入门（三）

一、更多查询

1.模糊查询

修改Category.xml，提供listCategoryByName查询语句select * from category where name like concat('%',#{0},'%')。concat('%',#{0},'%') 这是mysql的写法，如果是oracle，写法是select * from category_ where name like '%'||#{0}||'%'。

1 <select id="listCategoryByName" parameterType="string" resultType="Category">
2         select * from   category  where name like concat('%',#{0},'%')
3 </select>

1     private void queryByName() throws IOException {
2         create();
3         List<Category> categories = session.selectList("listCategoryByName", "i");
4         for (Category category : categories) {
5             System.out.println(category.getName());
6         }
7         close();
8     }

2.多条件查询

结合前面的模糊查询，多一个限定id的条件。因为是多个参数，而selectList方法又只接受一个参数对象，所以需要把多个参数放在Map里，然后把这个Map对象作为参数传递进去。

 1     private void queryByNameId() throws IOException {
 2         create();
 3         Map<String, Object> params = new HashMap<String, Object>();
 4         params.put("id", 8);
 5         params.put("name", "xiao");
 6         List<Category> categories = session.selectList("listCategoryByNameId", params);
 7         for (Category category : categories) {
 8             System.out.println(category.getName());
 9         }
10         close();
11     }

1     <select id="listCategoryByNameId" parameterType="map"
2         resultType="Category">
3         select * from category where id>#{id} and name like
4         concat('%',#{0},'%')
5     </select>

二、Mybatis的关系映射

1.一对多（一个分类对应多个产品）

<1>创建产品表以及产品表对应的实体。

 1 package mybatis.pojo;
 2 
 3 public class Product {
 4     private int id;
 5     private String name;
 6     private float price;
 7 
 8     public int getId() {
 9         return id;
10     }
11 
12     public void setId(int id) {
13         this.id = id;
14     }
15 
16     public String getName() {
17         return name;
18     }
19 
20     public void setName(String name) {
21         this.name = name;
22     }
23 
24     public float getPrice() {
25         return price;
26     }
27 
28     public void setPrice(float price) {
29         this.price = price;
30     }
31 
32     public String toString() {
33         return "Product [id=" + id + ", name=" + name + ", price=" + price + "]";
34     }
35 
36 }

<2>修改Category实体类，提供product集合。

 1 package mybatis.pojo;
 2 
 3 import java.util.List;
 4 
 5 public class Category {
 6     private int id;
 7     private String name;
 8     private List<Product> products;
 9 
10     public int getId() {
11         return id;
12     }
13 
14     public void setId(int id) {
15         this.id = id;
16     }
17 
18     public String getName() {
19         return name;
20     }
21 
22     public void setName(String name) {
23         this.name = name;
24     }
25 
26     public List<Product> getProducts() {
27         return products;
28     }
29 
30     public void setProducts(List<Product> products) {
31         this.products = products;
32     }
33 
34     public String toString() {
35         return "Category [id=" + id + ", name=" + name + "]";
36     }
37 }

<3>修改Category.xml

通过left join关联查询，对Category和Product表进行关联查询。与前面学习的有所区别，这里不是用的resultType, 而是resultMap，通过resultMap把数据取出来放在对应的对象属性里。

注： Category的id字段和Product的id字段同名，Mybatis不知道谁是谁的，所以需要通过取别名cid,pid来区分，name字段同理。

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper
 3     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 
 6 <mapper namespace="mybatis.pojo">
 7     <resultMap type="Category" id="categoryBean">
 8         <id column="cid" property="id" />
 9         <result column="cname" property="name" />
10 
11         <!-- 一对多关系 -->
12         <!-- property:指定的是集合属性的值，ofType：指的是集合中元素的类型 -->
13         <collection property="products" ofType="Product">
14             <id column="pid" property="id"></id>
15             <result column="pname" property="name" />
16             <result column="price" property="price" />
17         </collection>
18     </resultMap>
19     <!-- 关联查询分类和产品表 -->
20     <select id="listCategory" resultMap="categoryBean">
21         select c.*, p.*, c.id 'cid', p.id 'pid', c.name 'cname', p.name 'pname' from
22         category c left join product p on c.id = p.cid
23     </select>
24 </mapper>

<4>测试

 1 package mybatis.test;
 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.pojo.Category;
12 import mybatis.pojo.Product;
13 
14 public class testOneToMany {
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         List<Category> categories = session.selectList("listCategory");
23         for (Category c : categories) {
24             System.out.println(c);
25             List<Product> products = c.getProducts();
26             for (Product product : products) {
27                 System.out.println("	" + product.toString());
28             }
29         }
30         session.commit();
31         session.close();
32     }
33 
34 }

2.多对一（多个产品对应一个分类）

<1>修改Product.java，增加category属性

 1 package mybatis.pojo;
 2 
 3 import java.util.List;
 4 
 5 public class Category {
 6     private int id;
 7     private String name;
 8     private List<Product> products;
 9 
10     public int getId() {
11         return id;
12     }
13 
14     public void setId(int id) {
15         this.id = id;
16     }
17 
18     public String getName() {
19         return name;
20     }
21 
22     public void setName(String name) {
23         this.name = name;
24     }
25 
26     public List<Product> getProducts() {
27         return products;
28     }
29 
30     public void setProducts(List<Product> products) {
31         this.products = products;
32     }
33 
34     public String toString() {
35         return "Category [id=" + id + ", name=" + name + "]";
36     }
37 }

<2>新增Product.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper
 3     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 
 6 <mapper namespace="mybatis.pojo">
 7 
 8 
 9     <select id="getProduct" parameterType="int" resultType="Product">
10         select *
11         from product where id= #{id}
12     </select>
13 
14     <update id="updateProduct" parameterType="map">
15         update product
16         set cid=#{cid} where id=#{pid}
17     </update>
18 
19     <update id="updateProduct2" parameterType="Product">
20         update product
21         set cid=#{category.id} where id=#{id}
22     </update>
23 
24     <resultMap type="Product" id="productBean">
25         <id column="pid" property="id" />
26         <result column="pname" property="name" />
27         <result column="price" property="price" />
28 
29         <!-- 多对一关系 -->
30         <!-- property:指定的是集合属性的值，ofType：指的是集合中元素的类型 -->
31         <association property="category" javaType="Category">
32             <id column="cid" property="id" />
33             <result column="cname" property="name" />
34         </association>
35     </resultMap>
36     <!-- 关联查询分类和产品表 -->
37     <select id="listProduct" resultMap="productBean">
38         select c.*, p.*, c.id 'cid',
39         p.id 'pid', c.name 'cname', p.name 'pname' from
40         category c left join
41         product p on c.id = p.cid
42     </select>
43 </mapper>

通过listProduct配置关联查询的sql语句。然后通过resultMap ，进行字段和属性的对应。使用association 进行多对一关系关联，指定表字段名称与对象属性名称的一一对应关系。

注： Category的id 字段和Product的id字段同名，Mybatis不知道谁是谁的，所以需要通过取别名cid,pid来区分。name字段同理。

<3>在mybatis-config.xml中增加对于Product.xml的映射

1 <mapper resource="mybatis/pojo/Product.xml" />

<4>测试

 1 package mybatis.test;
 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.pojo.Category;
12 import mybatis.pojo.Product;
13 
14 public class testManyToOne {
15 
16     public static void update() throws IOException {
17         String resource = "mybatis-config.xml";
18         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
19         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
20         SqlSession session = sqlSessionFactory.openSession();
21 
22         Category category = session.selectOne("getCategory", 1);
23         Product product = session.selectOne("getProduct", 6);
24         product.setCategory(category);
25         session.update("updateProduct2", product);
26 
27         // Map<String, Integer> params = new HashMap<String, Integer>();
28         // params.put("cid", category.getId());
29         // params.put("pid", product.getId());
30         //
31         // session.update("updateProduct", params);
32 
33         session.commit();
34         session.close();
35     }
36 
37     public static void main(String[] args) throws IOException {
38         // TODO Auto-generated method stub
39         update();
40         String resource = "mybatis-config.xml";
41         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
42         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
43         SqlSession session = sqlSessionFactory.openSession();
44 
45         List<Product> products = session.selectList("listProduct");
46         for (Product product : products) {
47             System.out.println(product + "	对应的分类是：" + product.getCategory());
48 
49         }
50 
51         session.commit();
52         session.close();
53 
54     }
55 
56 }

练习：修改product(id=5)对应的类别为category(id=1)

两种解决思路

<1>首先查询id=5的product，再查询id=1的category，然后调用setCategory方法设置类别，然后对product进行更新操作。

<2>首先查询id=5的product，然后直接设置参数对product进行修改。

①先准备必要的sql语句。

Product.xml中

在updateProduct2中，因为product的成员变量中包含catergory对象，所以直接使用category.id获取类别的id。

 1     <select id="getProduct" parameterType="int" resultType="Product">
 2         select *
 3         from product where id= #{id}
 4     </select>
 5 
 6     <update id="updateProduct" parameterType="map">
 7         update product
 8         set cid=#{cid} where id=#{pid}
 9     </update>
10 
11     <update id="updateProduct2" parameterType="Product">
12         update product
13         set cid=#{category.id} where id=#{id}
14     </update>

Category.xml中

1     <select id="getCategory" parameterType="int" resultType="Category">
2         select *
3         from category where id= #{id}
4     </select>

②测试

第一种思路

 1     public static void update() throws IOException {
 2         String resource = "mybatis-config.xml";
 3         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
 4         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 5         SqlSession session = sqlSessionFactory.openSession();
 6 
 7         Category category = session.selectOne("getCategory", 1);
 8         Product product = session.selectOne("getProduct", 6);
 9         product.setCategory(category);
10         session.update("updateProduct2", product);
11 
12         session.commit();
13         session.close();
14     }

第二种思路

 1     public static void update() throws IOException {
 2         String resource = "mybatis-config.xml";
 3         InputStream inputStream = org.apache.ibatis.io.Resources.getResourceAsStream(resource);
 4         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
 5         SqlSession session = sqlSessionFactory.openSession();
 6 
 7         Product product = session.selectOne("getProduct", 6);
 8          Map<String, Integer> params = new HashMap<String, Integer>();
 9          params.put("cid", 1);
10          params.put("pid", product.getId());
11         
12          session.update("updateProduct", params);
13         session.commit();
14         session.close();
15     }

3.多对多（一张订单可以包含多种产品，一种产品可以出现在多张订单中）

为了维系多对多关系，必须要一个中间表。在这里我们使用订单项(OrderItem)表来作为中间表。

<1>建立order表，order_item表

<2>添加数据

1 INSERT INTO order_ VALUES (1,'code000A');
2 INSERT INTO order_ VALUES (2,'code000B');
3  
4 INSERT INTO order_item VALUES (null, 1, 1, 100);
5 INSERT INTO order_item VALUES (null, 1, 2, 100);
6 INSERT INTO order_item VALUES (null, 1, 3, 100);
7 INSERT INTO order_item VALUES (null, 2, 2, 100);
8 INSERT INTO order_item VALUES (null, 2, 3, 100);
9 INSERT INTO order_item VALUES (null, 2, 4, 100);

<3>添加实体类Order和OrderItem

①Order.java

 1 package mybatis.pojo;
 2 
 3 import java.util.List;
 4 
 5 public class Order {
 6     private int id;
 7     private String code;
 8     private List<OrderItem> orderItems;
 9 
10     public List<OrderItem> getOrderItems() {
11         return orderItems;
12     }
13 
14     public void setOrderItems(List<OrderItem> orderItems) {
15         this.orderItems = orderItems;
16     }
17 
18     public int getId() {
19         return id;
20     }
21 
22     public void setId(int id) {
23         this.id = id;
24     }
25 
26     public String getCode() {
27         return code;
28     }
29 
30     public void setCode(String code) {
31         this.code = code;
32     }
33 
34 }

②OrderItem.java

 1 package mybatis.pojo;
 2 
 3 public class OrderItem {
 4     private int id;
 5     private int number;
 6     private Order order;
 7     private Product product;
 8 
 9     public int getId() {
10         return id;
11     }
12 
13     public void setId(int id) {
14         this.id = id;
15     }
16 
17     public int getNumber() {
18         return number;
19     }
20 
21     public void setNumber(int number) {
22         this.number = number;
23     }
24 
25     public Order getOrder() {
26         return order;
27     }
28 
29     public void setOrder(Order order) {
30         this.order = order;
31     }
32 
33     public Product getProduct() {
34         return product;
35     }
36 
37     public void setProduct(Product product) {
38         this.product = product;
39     }
40 
41 }

<4>映射文件

①Order.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper
 3     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 
 6 <mapper namespace="mybatis.pojo">
 7     <resultMap type="Order" id="orderBean">
 8         <id column="oid" property="id" />
 9         <result column="code" property="code" />
10 
11         <collection property="orderItems" ofType="OrderItem">
12             <id column="oiid" property="id" />
13             <result column="number" property="number" />
14             <association property="product" javaType="Product">
15                 <id column="pid" property="id" />
16                 <result column="pname" property="name" />
17                 <result column="price" property="price" />
18             </association>
19         </collection>
20     </resultMap>
21 
22 
23     <select id="listOrder" resultMap="orderBean">
24         select o.*,p.*,oi.*, o.id
25         'oid', p.id 'pid', oi.id 'oiid', p.name 'pname'
26         from order_ o
27         left join
28         order_item oi on o.id =oi.oid
29         left join product p on p.id = oi.pid
30     </select>
31     <select id="getOrder" resultMap="orderBean">
32         select o.*,p.*,oi.*, o.id 'oid', p.id 'pid', oi.id 'oiid', p.name 'pname'
33         from order_ o
34         left join order_item oi on o.id =oi.oid
35         left join product p on p.id = oi.pid
36         where o.id = #{id}
37     </select>
38 </mapper>

②Product.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper
 3     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 
 6 <mapper namespace="mybatis.pojo">
 7 
 8     <!--  
 9     <select id="getProduct" parameterType="int" resultType="Product">
10         select *
11         from product where id= #{id}
12     </select>-->
13 
14     <update id="updateProduct" parameterType="map">
15         update product
16         set
17         cid=#{cid} where id=#{pid}
18     </update>
19 
20     <update id="updateProduct2" parameterType="Product">
21         update product
22         set
23         cid=#{category.id} where id=#{id}
24     </update>
25 
26     <resultMap type="Product" id="productBean">
27         <id column="pid" property="id" />
28         <result column="pname" property="name" />
29         <result column="price" property="price" />
30 
31         <!-- 多对一关系 -->
32         <!-- property:指定的是集合属性的值，ofType：指的是集合中元素的类型 -->
33         <association property="category" javaType="Category">
34             <id column="cid" property="id" />
35             <result column="cname" property="name" />
36         </association>
37     </resultMap>
38     <!-- 关联查询分类和产品表 -->
39     <select id="listProduct" resultMap="productBean">
40         select c.*, p.*, c.id 'cid',
41         p.id 'pid', c.name 'cname', p.name 'pname' from
42         category c left join
43         product p on c.id = p.cid
44     </select>
45     <select id="getProduct" resultMap="productBean">
46         select c.*, p.*, c.id 'cid', p.id 'pid', c.name 'cname', p.name 'pname'
47         from category c
48         left join product p on c.id = p.cid
49         where p.id = #{id}
50     </select>
51 </mapper>

③OrderItem.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper
 3     PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4     "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 
 6 <mapper namespace="mybatis.pojo">
 7     <insert id="addOrderItem" parameterType="OrderItem">
 8         insert into order_item
 9         values(null,#{order.id},#{product.id},#{number})
10     </insert>
11     <insert id="deleteOrderItem" parameterType="OrderItem">
12         delete from order_item
13         where oid = #{order.id} and pid = #{product.id}
14     </insert>
15 </mapper>

<5>修改mybatis-config.xml

1 <mapper resource="mybatis/pojo/Order.xml" />
2 <mapper resource="mybatis/pojo/OrderItem.xml" />

<6>查询操作

查询出所有的订单，然后遍历每个订单下的多条订单项，以及订单项对应的产品名称，价格，购买数量。通过Order.xml的listOrder对应的sql语句进行查询：

1     <select id="listOrder" resultMap="orderBean">
2         select o.*,p.*,oi.*, o.id
3         'oid', p.id 'pid', oi.id 'oiid', p.name 'pname'
4         from order_ o
5         left join
6         order_item oi on o.id =oi.oid
7         left join product p on p.id = oi.pid
8     </select>

联合order_, order_item_, product_ 三张表进行查询

 1     <resultMap type="Order" id="orderBean">
 2         <id column="oid" property="id" />
 3         <result column="code" property="code" />
 4 
 5         <collection property="orderItems" ofType="OrderItem">
 6             <id column="oiid" property="id" />
 7             <result column="number" property="number" />
 8             <association property="product" javaType="Product">
 9                 <id column="pid" property="id" />
10                 <result column="pname" property="name" />
11                 <result column="price" property="price" />
12             </association>
13         </collection>
14     </resultMap>

 1     private static void listOrder(SqlSession session) {
 2         List<Order> orders = session.selectList("listOrder");
 3         for (Order order : orders) {
 4             System.out.println(order.getCode());
 5             List<OrderItem> orderItems = order.getOrderItems();
 6             for (OrderItem orderItem : orderItems) {
 7                 System.out.format("	%s	%f	%d
", orderItem.getProduct().getName(), orderItem.getProduct().getPrice(),
 8                         orderItem.getNumber());
 9             }
10         }
11     }

<7>建立关系

　　建立了让订单000A和产品z建立了关系。首先通过id分别获取Ordre对象和Product对象，然后创建一个新的OrderItem对象，接着设置Order，设置Product，设置数量，最后调用"addOrderItem" 对应的sql语句插入数据。

 1     private static void addOrderItem(SqlSession session) {
 2         Order order = session.selectOne("getOrder", 1);
 3         Product product = session.selectOne("getProduct", 6);
 4         OrderItem orderItem = new OrderItem();
 5         orderItem.setProduct(product);
 6         orderItem.setOrder(order);
 7         orderItem.setNumber(200);
 8 
 9         session.insert("addOrderItem", orderItem);
10     }

addOrderItem调用insert into 语句插入一条OrderItem记录：

1     <insert id="addOrderItem" parameterType="OrderItem">
2         insert into order_item
3         values(null,#{order.id},#{product.id},#{number})
4     </insert>

<8>删除关系

删除了订单00A和产品z的关系，再次查询，就看不到产品z了。删除关系的时候，通过订单id(1)和产品id(6)进行删除。其实所谓的删除关系，就是删除掉OrderItem记录。

1     private static void deleteOrderItem(SqlSession session) {
2         Order order = session.selectOne("getOrder", 1);
3         Product product = session.selectOne("getProduct", 6);
4         OrderItem orderItem = new OrderItem();
5         orderItem.setProduct(product);
6         orderItem.setOrder(order);
7         session.delete("deleteOrderItem", orderItem);
8     }

练习：删除订单A，那么就应该删除订单A在订单项里所对应的数据。

通过Mybatis执行多条sql语句需要增加一个参数：allowMultiQueries，多条语句之间用分号隔开。

1 <property name="url" value="jdbc:mysql://localhost:3306/test2?characterEncoding=UTF-8&amp;allowMultiQueries=true" />

1     <delete id="deleteOrder" parameterType="Order">
2         delete from
3         order_ where code = #{code};
4         delete from
5         order_item
6         where oid = #{id}
7     </delete>

1     private static void deleteOrder(SqlSession session) {
2         Order order = session.selectOne("getOrder", 1);
3         session.delete("deleteOrder", order);
4     }

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原文地址：https://www.cnblogs.com/lyj-gyq/p/9230358.html