是对MyBatis-Plus的功能进行简单介绍,虽然是介绍,也让我们领略到他的优雅与强大。你是不是已经被吸引了?别着急,上一节,我们算是参观了MyBatis的风景,这一节,我将带你领略他独特的魅力。
官方表示,3.x支持Lambda表达式,那应该怎么使用呢?我们来看个例子:
QueryWrapper<Student> queryWrapper = new QueryWrapper<>(); queryWrapper.lambda().eq(Student::getName, "冯文议"); List<Student> studentList = list(queryWrapper); for (Student student : studentList) Console.info(student);看一下测试结果(为了看好,我们转成json):
{ "id":1035789714459471874, "name":"冯文议", "age":26, "info":"无畏造英雄", "isDelete":false, "createTime":"Sep 1, 2018 3:21:26 PM", "updateTime":"Sep 1, 2018 3:21:26 PM", "gender":"MALE", "idcardId":1035789714388168706, "cityId":1035762001753501698 }如果你使用了我的配置,你也能看到相应的SQL
==> Preparing: SELECT id,name,age,info,is_delete,create_time,update_time,gender,idcard_id,city_id FROM t_student WHERE name = ? ==> Parameters: 冯文议(String) <== Columns: id, name, age, info, is_delete, create_time, update_time, gender, idcard_id, city_id <== Row: 1035789714459471874, 冯文议, 26, <<BLOB>>, 0, 2018-09-01 15:21:26.0, 2018-09-01 15:21:26.0, 1, 1035789714388168706, 1035762001753501698 <== Total: 1感觉哈,分页查询是他们框架的起因,那我们先说分页查询。直接看代码:
第一步:在 Application 中配置
/** * 分页插件 */ @Bean public PaginationInterceptor paginationInterceptor() { return new PaginationInterceptor(); }第二步:写分页代码(为了你能够看得清楚,我截图给你):
看结果(json):
{ "records":[ { "id":1035788325322752001, "name":"1", "age":1, "info":"1", "isDelete":false, "createTime":"Sep 1, 2018 3:15:55 PM", "updateTime":"Sep 1, 2018 3:15:55 PM", "gender":"MALE", "idcardId":1035788325276614657, "cityId":1035788325201117185 }, { "id":1035789714459471874, "name":"冯文议", "age":26, "info":"无畏造英雄", "isDelete":false, "createTime":"Sep 1, 2018 3:21:26 PM", "updateTime":"Sep 1, 2018 3:21:26 PM", "gender":"MALE", "idcardId":1035789714388168706, "cityId":1035762001753501698 } ], "total":2, "size":2, "current":1, "optimizeCountSql":true }不要问我前端应该怎么写,表示我也不会写。
终于要进入这里了,是不是很激动啊。别急,客官,抽根烟先,我们慢慢来。
【1】多eq
QueryWrapper<Student> queryWrapper = new QueryWrapper<>(); queryWrapper.lambda() .eq(Student::getName, "冯文议") .eq(Student::getAge, 26); List<Student> studentList = list(queryWrapper); for (Student student : studentList) Console.info(new Gson().toJson(student));对于这部分的测试,我想结果是毫无因为,那么你应该关注什么呢?没错,SQL,所以,我们直接看SQL。当然,结果也是可以看到的。
==> Preparing: SELECT id,name,age,info,is_delete,create_time,update_time,gender,idcard_id,city_id FROM t_student WHERE name = ? AND age = ? ==> Parameters: 冯文议(String), 26(Integer) <== Columns: id, name, age, info, is_delete, create_time, update_time, gender, idcard_id, city_id <== Row: 1035789714459471874, 冯文议, 26, <<BLOB>>, 0, 2018-09-01 15:21:26.0, 2018-09-01 15:21:26.0, 1, 1035789714388168706, 1035762001753501698 <== Total: 1我们还可以这样写:
QueryWrapper<Student> queryWrapper = new QueryWrapper<>(); queryWrapper.lambda() .and(obj -> obj.eq(Student::getName, "冯文议") .eq(Student::getAge, 26)); List<Student> studentList = list(queryWrapper); for (Student student : studentList) Console.info(new Gson().toJson(student));【2】or
第一种:
QueryWrapper<Student> queryWrapper = new QueryWrapper<>(); queryWrapper.lambda() .or(obj1 -> obj1.eq(Student::getName, "冯文议")) .or(obj2 -> obj2.eq(Student::getName, "1")); List<Student> studentList = list(queryWrapper); for (Student student : studentList) Console.info(new Gson().toJson(student));sql:
SELECT * FROM t_student WHERE ( name = ? ) OR ( name = ? )第二种:
QueryWrapper<Student> queryWrapper = new QueryWrapper<>(); queryWrapper.lambda() .eq(Student::getName, "冯文议") .or() .eq(Student::getName, "1"); List<Student> studentList = list(queryWrapper); for (Student student : studentList) Console.info(new Gson().toJson(student));SQL:
SELECT * FROM t_student WHERE name = ? OR name = ?这样的话,我们就可以拼接各种条件了。那么问题来了:到底有哪些关键字呢?性能如何呢?
条件参数说明
查询方式说明setSqlSelect设置 SELECT 查询字段whereWHERE 语句,拼接 + WHERE 条件andAND 语句,拼接 + AND 字段=值andNewAND 语句,拼接 + AND (字段=值)orOR 语句,拼接 + OR 字段=值orNewOR 语句,拼接 + OR (字段=值)eq等于=allEq基于 map 内容等于=ne不等于<>gt大于>ge大于等于>=lt小于<le小于等于<=like模糊查询 LIKEnotLike模糊查询 NOT LIKEinIN 查询notInNOT IN 查询isNullNULL 值查询isNotNullIS NOT NULLgroupBy分组 GROUP BYhavingHAVING 关键词orderBy排序 ORDER BYorderAscASC 排序 ORDER BYorderDescDESC 排序 ORDER BYexistsEXISTS 条件语句notExistsNOT EXISTS 条件语句betweenBETWEEN 条件语句notBetweenNOT BETWEEN 条件语句addFilter自由拼接 SQLlast拼接在最后,例如:last(“LIMIT 1”)注意! xxNew 都是另起 ( ... ) 括号包裹。
如果官方提供的满足不了你的需求,或者你的需求很复杂,导致你不知道如何使用条件构造器,那应该怎么办呢?
很简单。
第一步:找到 Dao,写一个数据库操作接口
public interface StudentDao extends BaseMapper<Student> { List<Student> selectAll(); }第二步:在xml文件中写sql
<!--List<Student> selectAll();--> <select id="selectAll" resultMap="BaseResultMap"> select * from t_student </select>这样我们就可以使用了:
@Resource StudentDao studentDao; List<Student> studentList = studentDao.selectAll(); for (Student student : studentList) Console.info(new Gson().toJson(student));测试:
前面我们就说了,我是很不喜欢MP的查询接口的,我们就把他弄成我们喜欢的吧,我这里借鉴 JPA接口了,哈哈
interface:
/** * 查询所有数据 * @return List<Student> */ List<Student> findAll(); /** * 查询部分数据 * @return List<Student> */ List<Student> findList(); /** * 查询一条数据 * @return Student */ Student findOne(); /** * 根据主键ID查询数据 * @param id 主键ID,为null,返回null * @return Student */ Student findById(Long id);impl:
@Override public List<Student> findAll() { return list(null); } @Override public List<Student> findList() { return list(null); } @Override public Student findOne() { return getOne(null); } @Override public Student findById(Long id) { ExceptionUtil.notNull(id, "id must not null."); return getById(id); }我们来试一下:
哇!!!
是不是很爽!!!
[1] MyBatis-Plus测试示例
[2] 官网测试例子:WrapperTest.java