spring data jpa使用Pageable，ExampleMatcher进行分页多条件查询

一般简单的查询，可以使用，findByName,findById等方法，但是当这种方法越来越多的时候，就会显得特别冗杂，这个时候就需要把方法进行合并，spring data jpa提供了一种Query by Example的方法。

1. 当仅使用简单查询的时候

@Override
public Page queryByPage(T t, Pageable pageable) {
    Example example = Example.of(t);
    return baseDao.findAll(example, pageable);
}

这种查询会将实体中所有不为空的属性（包括父类的）都作为查询条件

SELECT roleentity0_.id AS id1_7_, roleentity0_.delete_flag AS delete_f2_7_, roleentity0_.system_id AS system_i3_7_, roleentity0_.create_time AS create_t4_7_, roleentity0_.create_user_id AS create_u5_7_, roleentity0_.update_time AS update_t6_7_, roleentity0_.update_user AS update_u7_7_, roleentity0_.content AS content8_7_, roleentity0_.org_id AS org_id9_7_, roleentity0_.role_name AS role_na10_7_, roleentity0_.role_type AS role_ty11_7_, roleentity0_.weight AS weight12_7_
FROM dafangzi_role roleentity0_
WHERE roleentity0_.update_time=? AND roleentity0_.create_time=? AND roleentity0_.delete_flag=?
ORDER BY roleentity0_.update_time DESC
LIMIT ?

1. 上述内容可以看到，由于修改时间和创建时间有默认值，也当成了查询条件，这并不是我们想要的，于是做出修改如下，

@Override
public Page queryByPage(T t, Pageable pageable) {
    //Example example = Example.of(t);
    ExampleMatcher matcher = ExampleMatcher.matching().withIgnorePaths("createTime", "updateTime");
    Example example = Example.of(t, matcher);
    return baseDao.findAll(example, pageable);
}

再查看查询结果，就是我们想要的结果了

SELECT roleentity0_.id AS id1_7_, roleentity0_.delete_flag AS delete_f2_7_, roleentity0_.system_id AS system_i3_7_, roleentity0_.create_time AS create_t4_7_, roleentity0_.create_user_id AS create_u5_7_, roleentity0_.update_time AS update_t6_7_, roleentity0_.update_user AS update_u7_7_, roleentity0_.content AS content8_7_, roleentity0_.org_id AS org_id9_7_, roleentity0_.role_name AS role_na10_7_, roleentity0_.role_type AS role_ty11_7_, roleentity0_.weight AS weight12_7_
FROM dafangzi_role roleentity0_
WHERE roleentity0_.delete_flag=?
ORDER BY roleentity0_.update_time DESC
LIMIT ?

1. 但是有很多时候我们查询的时候是需要模糊查询的，这个时候需要再次对需要模糊查询的字段进行特殊的处理

ExampleMatcher matcher = ExampleMatcher.matching().withIgnorePaths("createTime", "updateTime").withMatcher("roleName", match -> match.contains());
Example example = Example.of(roleEntity, matcher);
Page entityPage = roleService.queryByPage(example, PageRequest.of(page-1, limit, sort));

这样，就变成模糊查询了

SELECT roleentity0_.id AS id1_7_, roleentity0_.delete_flag AS delete_f2_7_, roleentity0_.system_id AS system_i3_7_, roleentity0_.create_time AS create_t4_7_, roleentity0_.create_user_id AS create_u5_7_, roleentity0_.update_time AS update_t6_7_, roleentity0_.update_user AS update_u7_7_, roleentity0_.content AS content8_7_, roleentity0_.org_id AS org_id9_7_, roleentity0_.role_name AS role_na10_7_, roleentity0_.role_type AS role_ty11_7_, roleentity0_.weight AS weight12_7_
FROM dafangzi_role roleentity0_
WHERE (roleentity0_.role_name LIKE ?) AND roleentity0_.delete_flag=?
ORDER BY roleentity0_.update_time DESC
LIMIT ?

附其它字符串处理的操作

参考链接：https://docs.spring.io/spring-data/jpa/docs/current/reference/html/

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