CODEWITHSUNDEEP
javaspring-bootjpaspring-data-jpa
Kerim
Kerim

Reputation: 125

How to check is there a row with getOne function

Assume that "Project" is POJO. In service layer of my project, I wrote a function that is get a row from table.

@Override
public ProjectDto getAProject(Long id) {
    try {
        Project project = projectRepository.getOne(id);
        if (project==null) {
            throw new IllegalArgumentException("Project not found");
        } else {
            return modelMapper.map(project, ProjectDto.class);
        }
    } catch (EntityNotFoundException ex) {
        throw new IllegalArgumentException("Project not found");
    }
}

The function is working fine with already exist id values. But if I give non-exist value, an exception occur like following. Looks like "getOne()" function don't throw "EntityNotFoundException".

ModelMapper mapping errors: Error mapping com.issuemanagement.entity.Project to com.issuemanagement.dto.ProjectDto

that means the exception come from model mapper logic. Because "project" object filled with null values so couldn't map to DTO class. I modified the function as following to fix this. 

@Override
public ProjectDto getAProject(Long id) {
    boolean isExist = projectRepository.existsById(id);
    if (isExist) {
        Project project = projectRepository.getOne(id);
        return modelMapper.map(project, ProjectDto.class);
    } else {
        throw new IllegalArgumentException("Project not found");
    }
}

but in this way the program goes to DB for two times. I don't like it. How can I do this operation with just one transaction?

BTW, if I try to run "toString()" function of "project", it throw "EntityNotFoundException" but it's looks like not official way. or it is? I hope there should be a boolean variable in somewhere.

Upvotes: 1

Views: 246

Answers (1)

Ken Chan
Ken Chan

Reputation: 90497

getOne() on JpaRepository will call getReference() on EntityManager under the hood which will return an instance whose state is lazily fetch .The EntityNotFoundException will not throw immediately but will only be thrown when its state is accessed at the first time .

It is normally used in the case that when you need to configure a @ManyToOne relationship for an entity (Let say configure a Department for an Employee) but you just have the ID of the related entity.(e.g. DepartmentId) . Using getOne() allows you to get a Department proxy instance such that you do not really need to query the database to get the actual Department instance just for setting up its relationship for an Employee.

In your case , you should use findById() which will return an empty Optional if the instance does not exist: 

@Override
public ProjectDto getAProject(Long id) {
   Project project = projectRepository.findById(id)
                    .orElseThrow(()->new IllegalArgumentException("Project not found"));

  return modelMapper.map(project, ProjectDto.class);
}

Upvotes: 2

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