Mybatis-Plus判断数据是否存在，不存在则插入

桃扇骨 2023-09-27 12:29 166阅读 0赞

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

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