【框架篇】Mybatis的内置方法，撸代码更快捷~~

掌握内置方法，在撸代码的过程中就可以让我们的代码更加简洁优雅，提高我们的开发效率，以下是我在日常开发中常用的方法，希望能帮助到大家，话不多说，直接上Demo~~~

一、insert ---------------- 新增

People people= new People();
people.setId("001");
people.setAge("18");
people.setName("xianYu");
peopleDAO.insert (people);

相当于：insert into people(id, age, name) values (‘001’, ‘18’, ‘xianYu’);

二、updateByPrimaryKey ---------------- 根据主键ID更新

People people= new People();
people.setId("001");
people.setAge("20");
people.setName("chouXianYu");
peopleDAO.updateByPrimaryKey(people);

相当于update people set age = ‘20’, name = ‘chouXianYu’ where id = ‘001’

三、selectByPrimaryKey ---------------- 根据主键ID查询

People people = new People();
people = peopleDAO.selectByPrimaryKey("001");

相当于select * form people where id = ‘001’；

四、selectByExample ---------------- 根据条件查询返回列表

Example exampl = new Example (People.class);
Criteria = criteria = exampl .createCriteria();
criteria.andNameEqualTo("xianYu");
criteria.andAgeIsNull();
exampl.setOrderByClause("name asc, age desc");
List<People> people = peopleDAO.selectByExample(exampl);

相当于：select * from people where name = ‘xianYu’ and age is null order by name asc,age desc;

当然在日常撸代码的时候我还是喜欢下面这种写法，各位看官也可以比较比较：

Example exampl = new Example (People.class);
Criteria = criteria = exampl .createCriteria();
criteria.andEqualTo("name","xianYu").andEqualTo("age","18");
List<People> people = peopleDAO.selectByExample(exampl);

相当于：select * from people where name = ‘xianYu’ and age = ‘18’;

Note：在iBator 生成的文件Example.java中包含一个static 的内部类 Criteria ，在Criteria中有很多方法，主要是定义SQL 语句where后的查询条件。

五、selectOne ---------------- 根据条件查询返回对象

 People people = new People();
 people.setName("xianYu");
 people.setAge("18");
 people = peopleDAO.selectOne(people);

相当于：select * from people where name = ‘xianYu’ and age = ‘18’;

Note： selectOne方法在使用的时候一定要对查询出的对象做盼空

六、countByExample ---------------->根据条件数量

Example exampl = new Example (People.class);
Criteria = criteria = exampl .createCriteria();
criteria.andNameEqualTo("xianYu");
int count = peopleDAO.countByExample(exampl);

相当于：select count(*) from people where name = ‘xianYu’;