JPA check if null query

Question

I use database query with JPA like that:

@Query("SELECT " + "new Report(" + "sum (r.fraction1)," + "sum (r.fraction2)) from Report r") Report calculateTotalReports();

When the database is full, it works fine, but when it is empty, the application crashes. How i can check when table contain rows and then select sum? I tried use CASE WHEN ... THEN, but JPA is not provide it.

Log of crashes:

QueryException: could not instantiate class [com.statistic.server.entity.Report] from tuple] with root cause

java.lang.IllegalArgumentException: null at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_201] at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) ~[na:1.8.0_201] at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) ~

JPQL clearly does allow CASE statements, datanucleus.org:15080/products/accessplatform_5_2/jpa/… and saying an application crashes is likely down to the application. Posting the actual exception would tell you where it is crashing, because a JPA provider should not "crash" when there is no data. — user3973283
– user3973283, Commented Feb 26, 2019 at 16:20
If your constructor says Report(double, double) try changing it to Report(Double, Double) and maybe you'll be fine. — MicSim
– MicSim, Commented Feb 26, 2019 at 16:35

Andrianekena Moise · Accepted Answer · 2019-02-26 16:36:07Z

I guess you can use COALESCE in this case then it will return 0 if r.fraction1 is null.

 @Query("SELECT " + "new Report(" + "COALESCE(sum(r.fraction1),0)," + "COALESCE(sum(r.fraction2),0)) from Report r")

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