Expected one result (or null) to be returned by selectOne(), but found: (不一定是sql语句返回值类型dao层问题)
如标题所讲,
Expected one result (or null) to be returned by selectOne(), but found: 。。
简单明了的报错,一般人在一般情况下想到的就是
1.查询一条数据,但返回多条数据:
2.查询多条数据,但是前台限制只能查询一条
从而回去检查相关的sql语句,sql语句中的返回值,相关的dao层代码。从而获取相关的解决办法,更改类的类型或者返回值类型等
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但是!当这些问题你全部排查一遍之后,还是会报这种错又是为什么呢?
今天做一个p2p项目,很简单的sql查询语句,出现了如题所示异常错误 —>
Expected one result (or null) to be returned by selectOne(), but found: 2
查看相关的sql语句发现,插入一条数据,紧接着查询该数据,却查到两个结果,而数据库也只有一条数据,跟预想不符。
再看sql语句及相关dao层
并没有发现相关错误
利用debug分析语句时
发现并没有相关查询到两个数据,但是还是报的相同的错误!
这个问题思索了好久,最终的解决办法竟然只是给创建的相关实体类进行序列化!!
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分析问题存在的原因:
1.因为当前做的项目是使用dubbo框架的maven工程,谈到此,可能有些人就应该了然,为什么要进行序列化了!
1)首先,我们需要理解什么是dubbo:Dubbo是一个框架;
Dubbo 是一个分布式服务框架,致力于提供高性能和透明化的 RPC 远程服务调用方案、服务治理方案。
2)运行dubbo框架的项目中为什么要序列化,
这是由dubbo相关特性决定的!
- 长连接:避免了每次调用新建TCP连接,提高了调用的响应速度
- 多路复用:单个TCP连接可交替传输多个请求和响应的消息,降低了连接的等待闲置时间,从而减少了同样并发数下的网络连接数,提高了系统吞吐量。
dubbo RPC主要用于两个dubbo系统之间作远程调用,特别适合高并发、小数据的互联网场景。
而序列化对于远程调用的响应速度、吞吐量、网络带宽消耗等同样也起着至关重要的作用,是我们提升分布式系统性能的最关键因素之一。
2.可是,为什么没序列化会造成类似于我这样的问题呢?
目前还在思考中。。等我再想想,不好意思
- 当Mybatis+sql遇到Expected one result (or null) to be returned by selectOne(), but found: 2时
- Expected one result (or null) to be returned by selectOne(), but found: 2问题完美解决
- Expected one result (or null) to be returned by selectOne(), but found: 2
- 遇到Expected one result (or null) to be returned by selectOne(), but found: 2怎么解决
- mybatis报错:Expected one result (or null) to be returned by selectOne(), but found: 20
- Expected one result (or null) to be returned by selectOne(), but found
- Expected one result (or null) to be returned by selectOne(), but found: 4
- Expected one result (or null) to be returned by selectOne(), but found: 2
- 错误TooManyResultsException: Expected one result (or null) to be returned by selectOne(), but found: 2
- Caused by: org.apache.ibatis.exceptions.TooManyResultsException: Expected one result (or null) to be returned by selectOne(), but found: 2
- Expected one result (or null) to be returned by selectOne(), but found: 2
- Expected one result (or null) to be returned by selectOne(), but found: 30
- Expected one result (or null) to be returned by selectOne(), but found: XX
- 关于Expected one result (or null) to be returned by selectOne(), but found: 3。。。。异常
- mybatis报错:Expected one result (or null) to be returned by selectOne(), but found: 20
- Expected one result (or null) to be returned by selectOne(), but found: 2
- Expected one result (or null) to be returned by selectOne(), but found: 20
- Expected one result (or null) to be returned by selectOne(), but found
- TooManyResultsException: Expected one result (or null) to be returned by selectOne(), but found: 3
- Mybatis报错|Expected one result (or null) to be returned by selectOne(), but found: 2