Spring JPA selecting specific columns

Question

I am using Spring JPA to perform all database operations. However I don't know how to select specific columns from a table in Spring JPA?

For example:
SELECT projectId, projectName FROM projects

Answer 1

You can use projections from Spring Data JPA (doc). In your case, create interface:

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

and add following method to your repository

List<ProjectIdAndName> findAll(); 

Answer 2

I don't like the syntax particularly (it looks a little bit hacky...) but this is the most elegant solution I was able to find (it uses a custom JPQL query in the JPA repository class):

@Query("select new com.foo.bar.entity.Document(d.docId, d.filename) from Document d where d.filterCol = ?1") List<Document> findDocumentsForListing(String filterValue); 

Then of course, you just have to provide a constructor for Document that accepts docId & filename as constructor args.