MyBatis详解（5）-- MyBatis注解

注解

映射器xml配置文件的缺陷：

1.繁琐：配置文件的书写本身繁琐，需要掌握的内容比较多

2.不直观：配置文件和接口直接只是名称相同，对应起来比较麻烦.

常用注解

1.基本注解：实现简单的增删改查操作。

@Insert 新增

@Options(useGeneratedKeys = true, keyProperty = “主键属性”) 主键回填

@Insert("insert into student(sname,birthday,ssex,classid) "
		+ "values(#{sname},#{birthday},#{ssex},#{classid})")
@Options(keyProperty = "sid",useGeneratedKeys = true)
public int addStu(Student s);

@SelectKey ( statement = “自增规则”, keyProperty = “主键属性”, resultType = 结果类型, before = true ) 主键自增

    @SelectKey ( statement = "select max(newsid) + 1 as newsId from news", keyProperty = "newsId", resultType = int.class, before = true )
    @Insert（...）
    public void addNews (News news);

@Delete 删除

    @Delete（“delete from student where sid= #{sId} ”）
    public int delStudent(int sid);

@Update 更新

    @Update（“update student set ssex =#{ssex}，classid = #{classid}）
    public int updateStudent(Student s);

@Selete 查询

	@Select("select * from student")
	public List<Student> findStudents();

传递多参

方法5：@Param 方式

	@Select("select * from student where ssex=#{xingbie} limit #{weizhi},#{sizepage}")
	public List<Student> findStudentsBysexpage(
			@Param("xingbie") String sex,
			@Param("weizhi") int curpage,
			@Param("sizepage") int sizepage
			);

2.结果映射注解：实现结果的映射关系，也可以完成级联映射。

@Results 结果映射

单表

	@Results(id = "stuMap" , value= {
			@Result(column = "sid", property = "sid"),
			@Result(column = "sname", property = "sname"),
			@Result(column = "birthday", property = "birthday"),
			@Result(column = "ssex", property = "ssex"),
			@Result(column = "classid", property = "classid")		
	})	
	@Select("select * from student")
	public List<Student> findStudent();

多表（相当于两个单表查询，之后再拼接）

一对一：@one

	@Results(id = "stuMap" , value= {
		@Result(column = "sid", property = "sid"),
		@Result(column = "sname", property = "sname"),
		@Result(column = "birthday", property = "birthday"),
		@Result(column = "ssex", property = "ssex"),
		@Result(column = "classid", property = "classid"),
			
		//一对一
		@Result(property = "bj",column = "classid" , 
		one = @One(select = "com.ape.mapper.ClassMapper.findBanjiList")
		)		
	})	
	@Select("select * from student")
	public List<Student> findStudentAndClass();

一对多：@many

	@Results(id= "class_map" , value = {
			@Result(column="classid",property="classid"),
			//一对多
			@Result(column = "classid",property = "slist",
					many = @Many(select = "com.ape.mapper.StudentMapper.findStudentByclassid")
			)
	})
	@Select("select * from class")
	public List<Banji> findBanjiAndStu();

3.动态SQL注解：实现动态 SQL 的内容 （3种方式）

1）脚本sql：XML配置方式的动态SQL，是用< script >的方式把它照搬过来，用注解来实现。适用于xml配置转换到注解配置

//脚本SQL
@Select("")
public List findStudents(Student s);

2）方法中构建sql：

	//在方法中构建动态SQL
	@UpdateProvider(type = StudentSql.class, method = "xiugaiStuSql")
	public int updateStudentFun(Student s);
	//内部类
		 class StudentSql{
		public String xiugaiStuSql(Student s) {
				String sql = "update student set ";
				
				if (s.getSsex() !=null) {
					sql += ",ssex =#{ssex}";
				}			
				if (s.getClassid() != 0) {				
					sql += ",classid =#{classid}";
				}
				sql += " where sid= #{sid}";
				sql = sql.replaceFirst(",", " ");
				
				return sql;
			}
		}

3）SQL 语句构造器：实现动态 SQL 的内容（推荐）

//SQL构造器
	@SelectProvider(type = StudentSql.class , method = "findGZQ")
	public List<Student> findStudentsGZQ(Student s);
	
	@InsertProvider(type = StudentSql.class , method = "gzqADD")
	public int addStudent(Student s);
	
	@UpdateProvider(type = StudentSql.class , method = "gzqUpdate")
	public int updateStudent(Student s);
	
	@DeleteProvider(type = StudentSql.class , method = "gzqDel")
	public int delStudent(int sid);
	
	public String findGZQ(Student s) {
				return new SQL() {
					{
						SELECT("*");
						FROM("student");
						if (s.getSsex() != null) {
							WHERE("ssex = #{ssex}");
						}
						if (s.getClassid() != 0) {
							OR();
							WHERE("classid = #{classid}");
						}
					}
				}.toString();
			} 
			 
			 public String gzqADD(Student s) {
				
				 return new SQL() {
					 
					 {
						INSERT_INTO("student"); 
						if (s.getSname() !=null) {
							VALUES("sname","#{sname}");
						}
						if (s.getBirthday() !=null) {
							VALUES("birthday","#{birthday}");
						}
		
						if (s.getSsex() !=null) {
							VALUES("ssex","#{ssex}");
						}
						if (s.getClassid() !=0) {
							VALUES("classid","#{classid}");
						}
						
					 }
				 }.toString();
			}
			 
			 public String gzqUpdate(Student s) {
				
				 return new SQL() {
					 {
						 UPDATE("student"); 
							if (s.getSname() !=null) {
								SET("sname = #{sname}");
							}
							if (s.getBirthday() !=null) {
								SET("birthday=#{birthday}");
							}
			
							if (s.getSsex() !=null) {
								SET("ssex=#{ssex}");
							}
							if (s.getClassid() !=0) {
								SET("classid= #{classid}");
							}
							
							WHERE("sid = #{sid}");
					 }
				 }.toString();
			}
			 
			 public String gzqDel(int sid) {
					
				 return new SQL() {
					 {
						 DELETE_FROM("student");
						 WHERE("sid = #{sid}");
					 }
				 }.toString();
			}
		}