java.lang.ClassCastException: java.util.HashMap cannot be cast to com.spacestudy.model.Investigator - spring-data-jpa

Question

I am trying to write test case for Repository method. In that Test case I want to test Investigator name using assertEquals(). Return type of method is set for that I use for each loop to retrieve result from set and then checked expected and actual result using assertEquals() but I am getting java.lang.ClassCastException: java.util.HashMap cannot be cast to com.spacestudy.model.Investigator
can any one please tell me what I am doing wrong in test case?
InvestigatorRepository
#Query("select new map(invest.sInvestigatorName as sInvestigatorName)"
+ " from Investigator invest")
Set<Investigator> findSinvestigatorName();
I tried Like this
#RunWith(SpringRunner.class)
#DataJpaTest
public class TestInvestigatorRepository {
#Autowired
public TestEntityManager testEm;
#Autowired
InvestigatorRepository investRepo;
#Test
public void testFindSinvestigatorName() {
Investigator invest = new Investigator();
invest.setsInvestigatorName("abc");
invest.setnInstId(60);
Investigator saveInDb = testEm.merge(invest);
Set<Investigator> getFromDb = investRepo.findSinvestigatorName();
for(Investigator result : getFromDb) {
assertEquals(saveInDb.getsInvestigatorName(),result.sInvestigatorName);
}
}
}
Stack Trace
java.lang.ClassCastException: java.util.HashMap cannot be cast to com.spacestudy.model.Investigator
at com.spacestudy.repository.TestInvestigatorRepository.testFindSinvestigatorName(TestInvestigatorRepository.java:39)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:252)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:538)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:760)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:206)

Answer 1

The HQL query you specify explicitly returns a Map, but the return type specified for the method specifies Set<Investigator> which are incompatible types, hence the error.
Spring Data tries to convert the types but fails and in the end, just tries to cast the result to the desired type.
In order to fix this you need to use compatible types options are:
let your query return Investigators.
let your query return a tuple by just listing the attributes: select invest.sInvestigatorName as sInvestigatorName from Investigator invest. Spring Data should be able to map that to an Investigator although your "interesting" property names might cause some troubles.
Since you are really just return a single attribute you might as well make the method return a Set<String> and use the query given in the previous point.