本文代码地址：https://github.com/hawkingfoo/java-web

一、概述

我们在写Mapper的时候，经常会通过注解的方式来写SQL语句，像下面这样。这要求我们传递的参数为一个具体的对象。

@Insert("INSERT INTO student (name, sex, addr) VALUES (#{name}, #{sex}, #{addr})")
int insert(Student stu);

但是，如果需要批量插入List<Student> studentList；不可能遍历studentList并依次执行插入语句，这样效率太差。
还有一种是配置Mybatis的xml文件，反正题主觉得那个配置好复杂。有没有还是通过注解的方式，执行批量操作呢？

二、批量执行

我们回想下SQL语句，插入一条记录：

INSERT INTO student (name, sex, addr) VALUES ("LiMing", 0, "Beijing");

批量插入：

INSERT INTO student (name, sex, addr) VALUES ("LiMing", 0, "Beijing"), ("LiNing", 0, "Shanghai");

根据 id 删除一条记录：

DELETE FROM student WHERE id = 1;

根据ids批量删除：

DELETE FROM student WHERE id IN (1, 2, 3);

三、方法

既然可以通过SQL语句批量执行，那我们可以修改注解。这里需要通过自定义Provider来实现。

@Component
@Mapper
public interface StudentMapper {
    @Insert("INSERT INTO student (name, sex, addr) VALUES (#{name}, #{sex}, #{addr})")
    int insert(Student stu);

    @InsertProvider(type = Provider.class, method = "batchInsert")
    int batchInsert(List<Student> students);

    @Select("SELECT * FROM student WHERE id = #{id}")
    Student selectById(@Param("id") int id);

    @DeleteProvider(type = Provider.class, method = "batchDelete")
    int batchDelete(List<Student> students);

    @Select("SELECT * FROM student")
    List<Student> selectAll();


    class Provider {
        /* 批量插入 */
        public String batchInsert(Map map) {
            List<Student> students = (List<Student>) map.get("list");
            StringBuilder sb = new StringBuilder();
            sb.append("INSERT INTO student (name,sex,addr) VALUES ");
            MessageFormat mf = new MessageFormat(
                    "(#'{'list[{0}].name}, #'{'list[{0}].sex}, #'{'list[{0}].addr})"
            );

            for (int i = 0; i < students.size(); i++) {
                sb.append(mf.format(new Object[] {i}));
                if (i < students.size() - 1)
                    sb.append(",");
            }
            return sb.toString();
        }

        /* 批量删除 */
        public String batchDelete(Map map) {
            List<Student> students = (List<Student>) map.get("list");
            StringBuilder sb = new StringBuilder();
            sb.append("DELETE FROM student WHERE id IN (");
            for (int i = 0; i < students.size(); i++) {
                sb.append("'").append(students.get(i).getId()).append("'");
                if (i < students.size() - 1)
                    sb.append(",");
            }
            sb.append(")");
            return sb.toString();
        }
    }
}