笔记：* 依赖MybatisPlus 3.5.5* 自动映射：a) 表名和实体类的映射 -> t_stu 表 Student 实体类:1.当表名和实体类名不一样的时候再实体类类名上加上@TableName注解@TableName("t_stu")2.也可以在配置文件中配置数据库表名的前缀，配置之后只要类名称与表名一致就无需@TableName注解mybatis-plus.global-config.db-config.table-prefix: tb_b) 字段名和实体类属性名(不是变量名，属性名是get/set方法中的setStuName中的StuName)的映射c) 字段名下划线命名方式和实体类属性小驼峰命名方式映射:mybatis-plus.configuration.map-underscore-to-camel-case: trued) 字段映射:1.字段名称与实体类属性名称不一致时，使用@TableField注解指定字段的名称即可完成封装@TableField(value= "XXX")2.字段失效，不希望该属性被查询，隐藏这个字段@TableField(select= false)e) 视图属性：有些字段不需要数据库存储，但需要展示，实体类中有这个有这个属性但数据库中不存在，叫视图属性。@TableField(exist = false)* 查询：(条件构造器、等值查询、范围查询、判断为空、包含查询、分组查询、聚合查询、排序查询、func查询、逻辑查询、自定义条件查询、last查询、exists查询、字段查询)1.条件构造器介绍(自己看源码)：Wrapper、AbstractWrapper、AbstractLambdaWrapper、QueryWrapper、LambdaQueryWrapper：a) Wrapper抽象类、子类是AbstractWrapperb) AbstractWrapper抽象类、子类是AbstractLambdaWrapper、QueryWrapperc) AbstractLambdaWrapper抽象类、子类是LambdaQueryWrapperd) QueryWrapper(重点掌握)继承于AbstractWrapper，非抽象类，字符串方式表示字段，创建该类对象。继承AbstractWrappere) LambdaQueryWrapper(重点掌握)继承于AbstractLambdaWrapper，非抽象类，方法引用方式表示字段，创建该类对象2.等值(eq)/不等值(ne)查询：a) 单个等值条件查询：QueryWrapper queryWrapper = new QueryWrapper();queryWrapper.eq("stu_name", "张三");LambdaQueryWrapper<Student> lambdaQueryWrapper = new LambdaQueryWrapper();lambdaQueryWrapper.eq(Student::getStuName, "张三");* 如果传递参数的值为null，将不作为查询条件(当参数不为null的时候作为查询条件)lambdaQueryWrapper.eq("param" != null, Student::getStuName, null);b) 多个条件查询，再加一个eq()，或者使用allEq(Map)或者allEq(Map, false)，后者设置false表示为null的字段舍弃，不进行查询。c) 范围查询：大于(gt): lambdaQueryWrapper.gt(Student::getStuAge, 18);大于等于(ge): lambdaQueryWrapper.ge(Student::getStuAge, 18);小于(lt): lambdaQueryWrapper.lt(Student::getStuAge, 18);小于等于(le): lambdaQueryWrapper.le(Student::getStuAge, 18);范围之间(between): lambdaQueryWrapper.between(Student::getStuAge, 18, 50);不在范围之间(notBetween): lambdaQueryWrapper.notBetween(Student::getStuAge, 18, 50);d) 模糊查询:like/notLike/likeLeft/likeRight/notLikeLeft/notLikeRight等lambdaQueryWrapper.like(Student::getStuName, "张");.......e) 判空查询:isNull/isNotNulllambdaQueryWrapper.isNull(Student::getStuName, "张");.....f) 包含查询: in/notIn/inSqlin/notIn:ArrayList<Integer> arrayList = new ArrayList<>();Collections.addAll(arrayList, 18,50,12);lambdaQueryWrapper.in(Student::getStuAge, arrayList);lambdaQueryWrapper.notIn(Student::getStuAge, arrayList);inSql: notInSql 反之ArrayList<Integer> arrayList = new ArrayList<>();Collections.addAll(arrayList, "18,50,13");demo1:lambdaQueryWrapper.inSql(Student::getStuAge, arrayList);demo2: 还可以传sql语句查询的结果lambdaQueryWrapper.inSql(Student::getStuAge, "select stu_age from t_stu where stu_age > 20");g) 分组查询:假设数据库的分组语句：select stu_sex,count(*) as sex_count from t_stu group by stu_sex;QueryWrapper queryWrapper = new QueryWrapper();// 指定分组的字段queryWrapper.groupBy("stu_sex");// 展示的字段queryWrapper.select("stu_sex,count(*) as sex_count");// 查询结果List<Map<String, Object>> list = studentMapper.selectMaps(queryWrapper);h) 聚合查询:假设数据库的分组语句(不能使用where)：select stu_sex,count(*) as sex_count from t_stu group by stu_sex having sex_count > 3;QueryWrapper queryWrapper = new QueryWrapper();// 指定分组的字段queryWrapper.groupBy("stu_sex");// 展示的字段queryWrapper.select("stu_sex,count(*) as sex_count");// 聚合条件筛选queryWrapper.having("sex_count >3");// 查询结果List<Map<String, Object>> list = studentMapper.selectMaps(queryWrapper);i) 排序查询: asc/desc1.orderByAsc:LambdaQueryWrapper<Student> lambdaQueryWrapper = new LambdaQueryWrapper();// 指定一个字段lambdaQueryWrapper.orderByAsc(Student::getStuAge);// 指定两个字段//lambdaQueryWrapper.orderByAsc(Student::getStuAge, Student::getId);studentMapper.selectList(lambdaQueryWrapper);2.orderByDesc ===> 同上 orderByAsc改为orderByDesc3.orderByorderBy(boolean condition, boolean isAsc, R column);a) condition – 执行条件,如果排序字段的值为null的时候, 是否还要作为排序字段b) isAsc – 是否是 ASC 排序c) column – 单个字段lambdaQueryWrapper.orderBy(true,true,Student::getStuAge);j) func查询:内嵌逻辑查询LambdaQueryWrapper<Student> lambdaQueryWrapper = new LambdaQueryWrapper();// 拼接不同的查询条件lambdaQueryWrapper.func(studentLambdaQueryWrapper -> {// 根据自己实际情况来做判断if (true) {studentLambdaQueryWrapper.gt(Student::getStuAge, 30);} else {studentLambdaQueryWrapper.gt(Student::getStuAge, 10);}});studentMapper.selectList(lambdaQueryWrapper);k) 逻辑查询: and/ora) and逻辑查询，sql: select * from t_stu where stu_age > 10 and stu_age < 30;LambdaQueryWrapper<Student> lambdaQueryWrapper = new LambdaQueryWrapper();lambdaQueryWrapper.gt(Student::getStuAge, 10).lt(Student::getStuAge, 30);studentMapper.selectList(lambdaQueryWrapper);b) and嵌套查询,sql: select * from t_stu where stu_sex = '女' and (stu_age> 18 or stu_age < 25);lambdaQueryWrapper.eq(Student::getStuSex, "女").and(studentLambdaQueryWrapper -> {studentLambdaQueryWrapper.gt(Student::getStuAge, 18).or().lt(Student::getStuAge, 25);});studentMapper.selectList(lambdaQueryWrapper);c) or逻辑查询:lambdaQueryWrapper.lt(Student::getStuAge, 30).or().gt(Student::getStuAge, 10);studentMapper.selectList(lambdaQueryWrapper);d) or内嵌套查询与and嵌套查询......e) nested逻辑查询: where后面拼接多个条件lambdaQueryWrapper.nested(i -> i.eq(Student::getStuName, "小舞").ne(Student::getStuAge, 40).eq(Student::getStuSex, "女"));拼接后的Sql: WHERE ((stu_name = ? AND stu_age <> ? AND stu_sex = ?))l) 自定义条件查询apply:直接写sql语句lambdaQueryWrapper.apply("id < 5");拼接后的Sql: WHERE (id < 5)m) last查询: 也是拼接字符串，拼接在SQL语句的最后面lambdaQueryWrapper.last("limit 0,3");拼接后的Sql: FROM t_stu limit 0,3n) exists查询:Sql: select * from t_stu where exists (select id from t_stu where stu_age = 1000);主查询: select * from t_stu子查询: (select id from t_stu where stu_age = 1000)当我们的子查询出的结果有值/结果集的时候，exists函数返回true，否者falseselect * from t_stu where true // 能讲所有数据查询出来select * from t_stu where false // 查询结果无数据1.exists函数返回的是boolean// 构建查询条件lambdaQueryWrapper.exists("select id from t_stu where stu_age = 18");拼接后的Sql: WHERE (EXISTS (select id from t_stu where stu_age = 18))2.notExists相反o) 字段查询:// select 查询要展示的字段lambdaQueryWrapper.select(Student::getId, Student::getStuAge,Student::getStuName);打印出的Sql: SELECT id,stu_age,stu_name FROM t_stu

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1.创建一个拦截器。给sql语句增加一个拦截器，然后把分页语句/参数拼接上去a) 创建mybatisPlus配置文件MybatisPlusConfig，在配置文件中添加分页插件// 官网 https://baomidou.com/pages/97710a/#%E6%94%AF%E6%8C%81%E7%9A%84%E6%95%B0%E6%8D%AE%E5%BA%93/*** 添加分页插件*/@Beanpublic MybatisPlusInterceptor mybatisPlusInterceptor() {MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));//如果配置多个插件,切记分页最后添加//interceptor.addInnerInterceptor(new PaginationInnerInterceptor()); 如果有多数据源可以不配具体类型 否则都建议配上具体的DbTypereturn interceptor;}b) 测试：方式一LambdaQueryWrapper<Student> lambdaQueryWrapper = new LambdaQueryWrapper<>();// 指定一个分页对象，包含对象的分页信息 IPage// long current 当前页, long size 每页显示条数// Page 是 IPage的接口实现类IPage<Student> studentPage = new Page<>(1, 3);// 执行查询IPage<Student> iPage = studentMapper.selectPage(studentPage, lambdaQueryWrapper);// 获取分页查询的信息System.out.println("当前页： " + iPage.getCurrent());System.out.println("每页显示的条数： " + iPage.getSize());System.out.println("总条数： " + iPage.getTotal());System.out.println("总页数： " + iPage.getPages());// 接受查询的结果List<Student> records = iPage.getRecords();records.forEach(i -> System.out.println(i));c) 测试：方式二1. Mapper层:// 自定义Sql查询IPage<Student> selectByStuName(IPage<Student> page, String stuName);2. XML:<select id="selectByStudentName" resultType="Student">select * from t_stu where stu_name = #{stuName}</select>3.运行:@Testvoid test02() {IPage<Student> studentPage = new Page<>(1,5);IPage<Student> iPage = studentMapper.selectByStudentName(studentPage, "安妮");List<Student> students = iPage.getRecords();students.forEach(i -> System.out.println(i));}