MyBatis中example.createCriteria()方法的具体使用
作者： 一枚码仔
MyBatis 的 Example 是一种用于动态查询构造的工具，允许开发者通过简单的 Java 对象来生成 SQL 语句。使用 Example，可以灵活地设置查询条件，例如使用链式调用指定字段、条件和排序等。它支持多种查询方式，如模糊查询、精确查询和范围查询，使得构建复杂的查询变得更加方便和直观。通过 Example，开发者可以减少手写 SQL 的工作量，提高代码的可读性和维护性。
一、mapper的crud方法:
1. insert方法
insert(User user)
插入一条数据，返回值是id
mapper.insert(User user)
insertSelective(User user)
插入一条数据，值为null的字段会做判空操作，不会添加 (推荐使用)
mapper.insertSelective(user)
2. select方法
selectByPrimaryKey(id)
根据主键查询，返回的是个对象
mapper.selectByPrimaryKey(id)
selectByExample(example)
根据条件查询，返回的是一个list
mapper.selectByExample(example)
selectCountByExample(example)
根据条件查询后计数，返回的是int
mapper.selectCountByExample(example)
3. update方法
updateByPrimaryKey(User user)
根据主键修改，返回的是int
mapper.updateByPrimaryKey(user)
updateByPrimaryKeySelective(User user)
根据主键修改不为null的字段，返回的是int (建议使用)
mapper.updateByPrimaryKeySelective(user)
updateByExample(User user, Example example)
根据条件修改，返回的是int，注意:前面的参数user是要修改的内容，后面的example是查询条件，查到结果后将结果按user的值修改
mapper.updateByExample(user, example)
updateByExampleSelective(User user, Example example)
根据条件修改不为null的字段，返回的是int (建议使用)
mapper.updateByExampleSelective(user, example)
4. delete方法
deleteByPrimaryKey(id)
根据主键删除，返回的是int
mapper.deleteByPrimaryKey(id)
deleteByExample(example)
根据条件删除，返回的是int
mapper.deleteByExample(example)
二、and / or方法
and方法
1. andEqualTo(“field”, value)
表示条件为实体类字段"field"等于value值
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andEqualTo("createUserId","1").andEqualTo("isDelete",0);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where( ( create_user_id = ? and is_delete = ? ) )
where后为什么会多两层括号我也不知道…反正查询结果是对的，下面为了美观和方便，就手动把括号去掉了
另一种单参数写法: 参数为map
Map<String, String> param = new HashMap<>();
param.put("createUserId","1");
param.put("isDelete","0");
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andEqualTo(param);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
2. andAllEqualTo（param）
与andEqualTo的单参数形式一样，参数为map
3. andNotEqualTo(“field”, value)
与andEqualTo相反，条件为实体类字段"field"不等于value值，同时此方法没有单参数
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andNotEqualTo("createUserId","1");
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where create_user_id <> ?
4. andIn(“field”, list)
表示条件为实体类"field"字段的值包含ids里的值，与sql语句中的in()相同
List<Integer> ids = new ArrayList<>();
ids.add(1);
ids.add(2);
Example example = new Example(WorkGuideModel.class); example.createCriteria().andIn("createUserId",ids);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where create_user_id in ( ? , ? )
list中不一定要是Integer类型，也可以是String
List<String> titles = new ArrayList<>();
titles.add("标题1");
titles.add("标题2");
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andIn("title",titles);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
举一反三:
与sql语句中的FIND_IN_SET]也相同
需要注意的是，FIND_IN_SET(str,strList)，这里的str为数据库中的字段名，如create_user_id，而不是实体类的createUserId
执行sql:
select * from tb_work_guide where FIND_IN_SET (create_user_id , ‘1,2’)
5. andNotIn(“field”, list)
与andIn()相反，查询"field"字段不包含list中的值的结果
执行sql:
select * from tb_work_guide where create_user_id not in ( ? , ? )
6. andIsNull(“field”)
表示实体类"field"字段为null
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andIsNull("createUserId");
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where create_user_id is null
7. andIsNotNull(“field”)
与andIsNull()相反，表示实体类"field"字段不为null
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andIsNotNull("createUserId");
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where create_user_id is not null
8. andBetween(“field”, value1, value2)
表示"field"字段的值在value1和value2之间，注意:这个区间是包头包尾的，1 <= field <= 7
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andBetween("createUserId",1,7);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where create_user_id between ? and ?
9. andNotBetween(“field”, value1, value2)
与andBetween()相反，表示"field"字段的值不在value1和value2之间,注意:这个区间也是包头包尾的，field < 1 或 field >7
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andNotBetween("createUserId",1,7);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where create_user_id not between ? and ?
10. andLike(“field”, str)
表示模糊查询，注意:需要自己拼接%或_
String str = "缴费";
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andLike("title","%"+str+"%");
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where title like ?
11. andNotLike(“field”, str)
与andLike相反的查询，也需要自己拼接%或_
String str = "缴费";
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andNotLike("title","%"+str+"%");
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where title not like ?
12. andGreaterThan(“field”, value)
表示查询"field"字段中大于value的值
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andGreaterThan("age",20);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where age > ?
13. andGreaterThanOrEqualTo(“field”, value)
与andGreaterThan()差不多，表示"field"字段中大于等于value的值
执行sql:
select * from tb_work_guide where age >= ?
14. andLessThan(“field”, value)
表示查询"field"字段中小于value的值
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andLessThan("age",20);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where age < ?
15. andLessThanOrEqualTo(“field”, value)
与andLessThan()差不多，表示"field"字段中小于等于value的值
执行sql:
select * from tb_work_guide where age <= ?
16. andCondition(condition)
在where后直接拼接条件，注意:此时拼接的field字段名是数据库的列名
写法1:
直接写完全where后面的条件语句，会自动将create_user_id = 1拼接到where后
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andCondition("create_user_id = 1");
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where create_user_id = 1
写法2:
andCondition(condition,value)，condition写查询字段(注意要记得加上=，不然会报错)，value传值，这样value值就可以写活了
Example example = new Example(WorkGuideModel.class);
example.createCriteria().andCondition("create_user_id = ",1);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where create_user_id = ?
andCondition()这个方法写的大佬都太少了，目前我只知道这是拼接作用的
or方法
or方法跟and方法其实差不多，只是and方法是在多条件中间拼接and，or方法是拼接or，下面就举几个例子加深印象，主要还是and和or一同使用
1. orEqualTo(param)
Map<String, String> param = new HashMap<>();
param.put("createUserId","1");
param.put("isDelete","0");
Example example = new Example(WorkGuideModel.class);
example.createCriteria().orEqualTo(param);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where create_user_id = ? or is_delete = ?
2. orIn(“field”, list)
List<String> titles = new ArrayList<>();
titles.add("标题1");
titles.add("标题2");
Example example = new Example(WorkGuideModel.class);
example.createCriteria().orIn("title", titles);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where title in ( ? , ? )
从sql中可以看到，orIn和andIn的执行sql是一样的，其余方法就不测试了，大概是一样的，只有多个条件时，中间的连接符号不同
如下:
Example example = new Example(WorkGuideModel.class);
example.createCriteria().orLike("title","%标题1%").orLike("createUserName","%小明%");
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where title like ? or create_user_name like ?
List<String> titles = new ArrayList<>();
titles.add("标题1");
titles.add("标题2");
Example example = new Example(WorkGuideModel.class);
example.createCriteria().orIn("title",titles).orLike("createUserName","%小明%");
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where title in ( ? , ? ) or create_user_name like ?
and和or一同使用
a and ( b or c)
Example example = new Example(WorkGuideModel.class);
Example.Criteria criteria = example.createCriteria();
criteria.andEqualTo("userId",1);
Example.Criteria criteria2 = example.createCriteria();
criteria2.orLike("title","%标题%").orBetween("age",1,5);
example.and(criteria2);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where ( ( user_id = ? ) and ( title like ? or age between ? and ? ) )
(a and b) or (c or d)
List<String> titles = new ArrayList<>();
titles.add("标题1");
titles.add("标题2");
Example example = new Example(WorkGuideModel.class);
Example.Criteria criteria = example.createCriteria();
criteria.andEqualTo("userId",1).andIn("title",titles);
Example.Criteria criteria2 = example.createCriteria();
criteria2.orLike("name","%小明%").orBetween("age",1,5);
example.or(criteria2);
List<WorkGuideModel> list = mapper.selectByExample(example);
return list;
执行sql:
select * from tb_work_guide where ( create_user_id = ? and title in ( ? , ? ) ) or ( title like ? or open between ? and ? )
将代码中的example.or(criteria2);改成example.and(criteria2);后会发现sql变成了:
select * from tb_work_guide where ( create_user_id = ? and title in ( ? , ? ) ) and ( title like ? or open between ? and ? )
总结:
多条件查询时，可以直接使用同一个条件构造器，往里面直接添加条件就行。多重条件查询时，如上面的两个括号中的条件都要分别满足时，可以分别创建条件构造器，然后分别往里添加条件
Example.Criteria criteria = example.createCriteria(); Example.Criteria criteria2 = example.createCriteria();
两个括号之间(也就是两个条件构造器之间)使用example的and或or来连接
example.and(criteria2); example.or(criteria2);
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