Mybatis进阶学习笔记——动态sql

1.if标签

     <select id="queryByNameAndTelephone" parameterType="Customer"
         resultType="Customer">
         SELECT * FROM t_customer
         WHERE 1=1
         <if test="name!=null and name!=''">
             AND NAME LIKE #{name}
         </if>
         <if test="telephone!=null and telephone!=''">
             AND telephone LIKE #{telephone}
         </if>
     </select>

public List<Customer> queryByNameAndTelephone(Customer customer);

     /**
      * if标签使用
      */
     @Test
     public void test1() {
         SqlSession sqlSession = SessionUtils.getSession();
         // getMapper(): 返回指定接口的动态代理的实现类对象
         CustomerDao dao = sqlSession.getMapper(CustomerDao.class);
         Customer c = new Customer();
         //c.setName("%陈%");
         c.setTelephone("%55%");
         List<Customer> list = dao.queryByNameAndTelephone(c);
         for (Customer customer : list) {
             System.out.println(customer);
         }
         sqlSession.commit();
         sqlSession.close();
     }

2.where标签：自动把第一个条件的and去掉

     <select id="queryByNameAndTelephone" parameterType="Customer"
         resultType="Customer">
         SELECT * FROM t_customer
         <!-- <where>：where条件，自动把第一个条件的and去掉 -->
         <where>
             <if test="name!=null and name!=''">
                 AND NAME LIKE #{name}
             </if>
             <if test="telephone!=null and telephone!=''">
                 AND telephone LIKE #{telephone}
             </if>
         </where>
     </select>

3.sql片段

作用：把相同的sql片段抽取出来

     <!-- sql片段 -->
     <sql id="customerField">
         id,name,gender,telephone
     </sql>

     <select id="queryByNameAndTelephone" parameterType="Customer"
         resultType="Customer">
         SELECT
         <include refid="customerField"/>
         FROM t_customer
         <!-- <where>：where条件，自动把第一个条件的and去掉 -->
         <where>
             <if test="name!=null and name!=''">
                 AND NAME LIKE #{name}
             </if>
             <if test="telephone!=null and telephone!=''">
                 AND telephone LIKE #{telephone}
             </if>
         </where>
     </select>

4.foreach标签

     <delete id="deleteCustomerByIn" parameterType="Customer">
         DELETE FROM t_customer WHERE
         <!--
             collection: 需要遍历的属性
             item: 遍历的变量
             open: 循环前面的 sql语句
             close： 循环后面的 sql语句
             separator：分隔符
 
             id IN(1,2,3)
          -->
          <!-- id为ids数组中的每个元素 -->
         <foreach collection="ids" item="id" open="id IN (" close=")" separator=",">
             #{id}
         </foreach>
     </delete>

public void deleteCustomerByIn(Customer customer);

     /**
      * foreach标签
      */
     @Test
     public void test2() {
         SqlSession sqlSession = SessionUtils.getSession();
         // getMapper(): 返回指定接口的动态代理的实现类对象
         CustomerDao dao = sqlSession.getMapper(CustomerDao.class);
         Customer c = new Customer();
         Integer[] ids = {23,24,25};
         c.setIds(ids);
         dao.deleteCustomerByIn(c);
         sqlSession.commit();
         sqlSession.close();
     }

Customer.java：

 package cn.sm1234.domain;
 
 import java.util.Arrays;
 
 public class Customer {
 
     private Integer id;
     private String name;
     private String gender;
     private String telephone;
 
     private Integer ids[];
 
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public String getGender() {
         return gender;
     }
     public void setGender(String gender) {
         this.gender = gender;
     }
     public String getTelephone() {
         return telephone;
     }
     public void setTelephone(String telephone) {
         this.telephone = telephone;
     }
     public Integer[] getIds() {
         return ids;
     }
     public void setIds(Integer[] ids) {
         this.ids = ids;
     }
     @Override
     public String toString() {
         return "Customer [id=" + id + ", name=" + name + ", gender=" + gender + ", telephone=" + telephone + ", ids="
                 + Arrays.toString(ids) + "]";
     }
 
 }