How to Select Specific Columns in Spring JPA Using Projections?

Custom Column Selection in Spring JPA

Selecting specific columns from a table in Spring JPA allows you to retrieve only the data you need, reducing bandwidth and improving performance. Here's how you can achieve this using Spring Data JPA:

Using Projections

Spring Data JPA supports projections, which allow you to create custom interfaces that define the columns you want to retrieve. For instance, for the example query mentioned:

SELECT projectId, projectName FROM projects

you would create an interface:

interface ProjectIdAndName {
    String getId();
    String getName();
}

Repository Method

Next, add a method to your repository that returns the desired projection:

List<ProjectIdAndName> findAll();

By calling the findAll method, you can retrieve a list of objects that contain only the id and name properties, without fetching the entire row data.

Example Usage

To use this feature, inject the repository into your service or controller and call the findAll method as usual:

@Autowired
private ProjectRepository projectRepository;

@GetMapping("/projects")
public List<ProjectIdAndName> getAllProjects() {
    return projectRepository.findAll();
}

This will return a list of ProjectIdAndName objects, containing the selected columns for each project.

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