一、Wrapper介绍
Wrapper ： 条件构造抽象类，最顶端父类
- AbstractWrapper ： 用于查询条件封装，生成 sql 的 where 条件
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- QueryWrapper ： 查询条件封装
- UpdateWrapper ： Update 条件封装
- AbstractLambdaWrapper ： 使用Lambda 语法
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- LambdaQueryWrapper ：用于Lambda语法使用的查询Wrapper
- LambdaUpdateWrapper ： Lambda 更新封装Wrapper
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条件构造器是一个用于构建SQL查询条件的工具，它可以帮助你通过链式调用来拼装查询条件，进一步简化了查询条件的编写。使用条件构造器，你可以灵活地构建各种条件，包括等于、不等于、大于、小于、模糊查询等。
二、QueryWrapper
a>例1：组装查询条件
/** 查询用户包含a,年龄在20到30之间，邮箱信息不为null的用户信息 **/
@Test
public void test01() {
/*
SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user
WHERE is_deleted=0 AND (user_name LIKE ?
AND age BETWEEN ? AND ? AND email IS NOT NULL)
*/
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.like("user_name", "a")
.between("age", 20, 30)
.isNotNull("email");
List<User> users = userMapper.selectList(queryWrapper);
users.forEach(System.out::println);
}b>例2：组装排序条件
/** 组装排序条件 查询用户信息，按照年龄的降序排序，若年龄相同，则按照id升序排序 **/
@Test
public void test02() {
/*
SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user
WHERE is_deleted=0 ORDER BY age DESC,uid ASC
*/
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.orderByDesc("age")
.orderByAsc("uid");
List<User> users = userMapper.selectList(queryWrapper);
users.forEach(System.out::println);
}c>例3：组装删除条件
/** 组装删除条件 删除邮箱地址为null的用户信息 **/
@Test
public void test03() {
/*
UPDATE t_user SET is_deleted=1 WHERE is_deleted=0 AND (email IS NOT NULL)
*/
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.isNull("email");
int result = userMapper.delete(queryWrapper);
System.out.println("result = " + result);
}d>例4：条件的优先级
/** 组装修改条件 将(年龄大于20并且用户名中包含有a)或邮箱为null的用户信息修改 **/
@Test
public void test04() {
/*
UPDATE t_user SET user_name=?, email=?
WHERE is_deleted=0 AND (age > ? AND user_name LIKE ? OR email IS NOT NULL)
*/
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.gt("age", 20)
.like("user_name", "a")
.or()
.isNotNull("email");
User user = new User();
user.setName("小明");
user.setEmail("test@atguigu.com");
int result = userMapper.update(user, queryWrapper);
System.out.println("result = " + result);
}
/** 条件优先级 将用户名中包含a并且(年龄大于20或邮箱为null)的用户信息修改 **/
@Test
public void test05() {
// lambda中条件优先级
/*
UPDATE t_user SET user_name=?, email=?
WHERE is_deleted=0 AND (user_name LIKE ? AND (age > ? OR email IS NULL))
*/
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.like("user_name", "a")
.and(i -> i.gt("age", 20).or().isNull("email"));
User user = new User();
user.setName("小红");
user.setEmail("test@atguigu.com");
int result = userMapper.update(user, queryWrapper);
System.out.println("result = " + result);
}e>例5：组装select子句（查询部分字段）
/** 组装select字句 查询用户名的用户名、年龄、邮箱信息 **/
@Test
public void test06() {
/*
SELECT user_name,age,email FROM t_user WHERE is_deleted=0
*/
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.select("user_name", "age", "email");
List<Map<String, Object>> users = userMapper.selectMaps(queryWrapper);
users.forEach(System.out::println);
}f>例6：实现子查询
/** 组装子查询 查询id小于100的用户信息**/
@Test
public void test07() {
/*
SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user
WHERE is_deleted=0 AND (uid IN (select uid from t_user where uid <= 100))
*/
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.inSql("uid", "select uid from t_user where uid <= 100");
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}三、UpdateWrapper
/** 使用UpdateWrapper实现修改功能 将用户名中包含a并且(年龄大于20或邮箱为null)的用户信息修改 **/
@Test
public void test08() {
/*
UPDATE t_user SET user_name=?,email=?
WHERE is_deleted=0 AND (user_name LIKE ? AND (age > ? OR email IS NULL))
*/
UpdateWrapper<User> updateWrapper = new UpdateWrapper<>();
updateWrapper.like("user_name", "a")
.and(i -> i.gt("age", 20).or().isNull("email"));
updateWrapper.set("user_name", "小黑").set("email", "abc@atguigu.com");
int result = userMapper.update(null, updateWrapper);
System.out.println("result = " + result);
}
四、使用condition组装条件
在真正开发的过程中，组装条件是常见的功能，而这些条件数据来源于用户输入，是可选的，因此我们在组装这些条件时，必须先判断用户是否选择了这些条件，若选择则需要组装该条件，若没有选择则一定不能组装，以免影响SQL执行的结果
思路一：
使用if判断语句
/** 模拟开发中组装条件的情况 **/
@Test
public void test09() {
/*
SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user
WHERE is_deleted=0 AND (user_name LIKE ? AND age <= ?)
*/
String username = "a";
Integer ageBegin = null;
Integer ageEnd = 30;
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
if (StringUtils.isNotBlank(username)) {
// isNotBlank判断某个字符串是否不为空字符串、不为null、不为空白符
queryWrapper.like("user_name", username);
}
if (ageBegin != null) {
queryWrapper.gt("age", ageBegin);
}
if (ageEnd != null) {
queryWrapper.le("age", ageEnd);
}
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}思路二：
使用带condition参数的重载方法构建查询条件，简化代码的编写
以like举例，condition用于做判断
/** 使用condition组装条件 **/
@Test
public void test10() {
/*
SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user
WHERE is_deleted=0 AND (user_name LIKE ? AND age <= ?)
*/
String username = "a";
Integer ageBegin = null;
Integer ageEnd = 30;
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.like(StringUtils.isNotBlank(username), "user_name", username)
.gt(ageBegin != null, "age", ageBegin)
.le(ageEnd != null, "age", ageEnd);
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}五、LambdaQueryWrapper
功能等同于QueryWrapper，提供了Lambda表达式的语法可以避免填错列名。
/** LambdaQueryWrapper **/
@Test
public void test11() {
/*
SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user
WHERE is_deleted=0 AND (user_name LIKE ? AND age <= ?)
*/
String username = "a";
Integer ageBegin = null;
Integer ageEnd = 30;
//组装set子句
LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
//避免使用字符串表示字段，防止运行时错误
queryWrapper.like(StringUtils.isNotBlank(username), User::getName, username)
.gt(ageBegin != null, User::getAge, ageBegin)
.le(ageEnd != null, User::getAge, ageEnd);
List<User> list = userMapper.selectList(queryWrapper);
list.forEach(System.out::println);
}六、LambdaUpdateWrapper
/** LambdaUpdateWrapper **/
@Test
public void test12() {
/*
UPDATE t_user SET user_name=?,email=?
WHERE is_deleted=0 AND (user_name LIKE ? AND (age > ? OR email IS NULL))
*/
LambdaUpdateWrapper<User> updateWrapper = new LambdaUpdateWrapper<>();
updateWrapper.like(User::getName, "a")
//lambda表达式内的逻辑优先运算
.and(i -> i.gt(User::getAge, 20).or().isNull(User::getEmail));
updateWrapper.set(User::getName, "小黑").set(User::getEmail, "abc@atguigu.com");
int result = userMapper.update(null, updateWrapper);
System.out.println("result = " + result);
}
