How Can Spring JPA Fetch Only Specific Columns from a Database Table?

Using Spring JPA to Fetch Specific Columns

When using Spring JPA for database operations, the need arises to retrieve only specific columns from a table. This can be achieved through projections, a feature provided by Spring Data JPA.

Implementing Projections

To project only the required columns, create a Java interface that extends the Iterable interface. The interface should declare methods that correspond to the targeted columns. For instance:

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

Applying Projections in Repository

Integrate the projections into your repository by adding a method that returns the projected data. In this case, to fetch the projectId and projectName columns:

List<ProjectIdAndName> findAll();

By invoking the findAll() method on the repository, you can obtain a list of projection objects, each containing the specified columns. Spring JPA will handle the underlying SQL query construction and projection mapping automatically.

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