Mybatis-Plus判断数据是否存在，不存在则插入

今天写业务代码有这么一个场景，就是在数据库表中插入一条数据，并且这个表中只有这么一条。

因为是用的Mybatis-Plus所以直接用它来实现业务功能，起初是把要插入的数据放到mybatis-plus中，代码如下

LambdaQueryWrapper wrapper = new LambdaQueryWrapper<>();        wrapper.eq(ProjectCompany::getProjectId,projectId).eq(ProjectCompany::getCompanyId,user.getCompanyId()).eq(ProjectCompany::getIsDelete,"0");        List projectCompanies = projectCompanyMapper.selectList(wrapper);

LambdaQueryWrapper wrapper = new LambdaQueryWrapper<>();wrapper.eq(ProjectCompany::getProjectId,projectId).eq(ProjectCompany::getCompanyId,user.getCompanyId()).eq(ProjectCompany::getIsDelete,"0");List projectCompanies = projectCompanyMapper.selectList(wrapper);

就是把要插入的数据先在表中查出来是否存在，查出来的结果放到List集合中，但是在遍历时始终想不到合适的思路，起初是这样写的

for (ProjectCompany projectCompany1 : projectCompanies) {            if (!(projectCompany1.getCompanyId().equals(projectCompany.getCompanyId())) && !(projectCompany1.getProjectId().equals(projectCompany.getProjectId()))){                projectCompanyMapper.insert(projectCompany);                break;            }        }

for (ProjectCompany projectCompany1 : projectCompanies) {    if (!(projectCompany1.getCompanyId().equals(projectCompany.getCompanyId())) && !(projectCompany1.getProjectId().equals(projectCompany.getProjectId()))){        projectCompanyMapper.insert(projectCompany);        break;    }}

因为不知道 if (!(projectCompany1.getCompanyId().equals(projectCompany.getCompanyId())) && !(projectCompany1.getProjectId().equals(projectCompany.getProjectId())))   （大家对这个有什么解决办法，欢迎留言给c主提供一下） 该怎么判断。试来试去始终不行，后面就换了一种思路，不查所有数据了，我只在表中查一条

LambdaQueryWrapper wrapper = new LambdaQueryWrapper<>();        wrapper.eq(ProjectCompany::getProjectId,projectCompany.getProjectId()).eq(ProjectCompany::getCompanyId,projectCompany.getCompanyId()).eq(ProjectCompany::getIsDelete,"0");ProjectCompany projectCompany1 = projectCompanyMapper.selectOne(wrapper);            if (projectCompany1 ==null){                projectCompanyMapper.insert(projectCompany);            }

LambdaQueryWrapper wrapper = new LambdaQueryWrapper<>();
        wrapper.eq(ProjectCompany::getProjectId,projectCompany.getProjectId()).eq(ProjectCompany::getCompanyId,projectCompany.getCompanyId()).eq(ProjectCompany::getIsDelete,"0");
ProjectCompany projectCompany1 = projectCompanyMapper.selectOne(wrapper);
            if (projectCompany1 ==null){
                projectCompanyMapper.insert(projectCompany);
            }

就是我还用之前的查询条件，只不过这次查询我查一条数据projectCompanyMapper.selectOne(wrapper);

然后判断这个结果是不是空的，如果是空的则说明数据库中没有该数据，则可以进行插入。相反如果不为空，则说明表中有数据。

但是上面代码还会出现一个异常，就是   projectCompanyMapper.selectOne(wrapper);  可能会查出多条数据，所以我们还要对该异常进行一个处理

try {            ProjectCompany projectCompany1 = projectCompanyMapper.selectOne(wrapper);            if (projectCompany1 ==null){                projectCompanyMapper.insert(projectCompany);            }        }catch (Exception e){            throw new BaseException("数据有误，待周一回来调试,原因是ProjectCompany表中");        }

try {    ProjectCompany projectCompany1 = projectCompanyMapper.selectOne(wrapper);    if (projectCompany1 ==null){        projectCompanyMapper.insert(projectCompany);    }}catch (Exception e){    throw new BaseException("数据有误，待周一回来调试,原因是ProjectCompany表中");}

因为是周五，要着急下班，所以异常信息自己定义的一个，今天就说这么多吧。

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来源地址：https://blog.csdn.net/xiaoheihai666/article/details/127695556