JPA native query with same column twice - spring-boot

Question

I am a JPA newbie and wanted to have a JPA native query for a single table (below) which I would like to fetch in my #Entity based class called TestRequest. It has a column 'RequestTime' that is fetched with DAYNAME() and then with DATEDIFF() functions.
SELECT TestRequest.Id AS Id
, TestRequest.RequestTime AS RequestTime
, DAYNAME(TestRequest.RequestTime) AS RequestDay
, TestRequest.StatusMessage AS StatusMessage
, DATEDIFF(CURDATE(), TestRequest.RequestTime) AS HowLongAgo
FROM TestRequest
LEFT JOIN TestRun
ON TestRequest.TestRunId = TestRun.Id
WHERE Requestor = '[NAME]'
ORDER BY Id DESC
Is there any way in which the column (fetched second time as HowLongAgo) be set into a property which is not mapped to a table column within the TestRequest class? Are there any field level annotations for this?

Answer 1

You need to use Interface-based projections:
You will need to create an interface that define the getters for each field in your projection like:
public interface RequestJoinRunProjection {
int getId();
LocalDate getRequestTime();
String getMessage();
String getRequestDay();
Long getHowLongAgo();
}
Then you define a method on your Repository that has the native query you want to run:
public interface TestRequestRepository extends CrudRepository<TestRequest, Long> {
// Any other custom method for TestRequest entity
#Query(value = "SELECT trq.Id AS id " +
" , trq.RequestTime AS requestTime " +
" , DAYNAME(trq.RequestTime) AS requestDay " +
" , trq.StatusMessage AS statusMessage " +
" , DATEDIFF(YEAR, CURDATE(), trq.RequestTime) AS howLongAgo " +
"FROM TestRequest trq " +
" LEFT JOIN TestRun tr " +
" ON trq.TestRunId = tr.Id " +
"WHERE Requestor = ?1 ORDER BY Id DESC"), nativeQuery = true)
List<RequestJoinRunProjection> findTestSumary(String name);
}
Notice query must be native since you are using database functions, also the column names must match the setters of your projection interface(following bean rules), so use AS in order to change the names in your query.
I strongly suggest you test your query on h2 before injecting into #Query annotation. DATEDIFF requires 3 parameters.