Creating custom functions in Spring Boot services - spring

Question

I am writing a simple Spring Boot Application.I'm creating a repository,then its service and then its implementation
The code works fine if I use inbuilt functions of the JPA repository.
However it throws error if I try to make a function in the service interface.
If I make that function in the repository it doesn't throw that error
Here is the code:
Repository:
#Transactional
public interface Local_Repository extends JpaRepository<LocalModel,Long> {
}
Service:
public interface Local_Service {
public List<LocalModel> findAll();
public LocalModel findById(Long id);
public LocalModel findBymo(String mo);//this is the function I added
}
Implementation:
#Service
public class Local_Impl implements Local_Service {
#Autowired
private Local_Repository repository;
#Override
public List<LocalModel> findAll() {
List<LocalModel> cities = (List<LocalModel>) repository.findAll();
return cities;
}
#Override
public LocalModel findById(Long id) {
LocalModel city = repository.findOne(id);
return city;
}
#Override //this throws error
public LocalModel findBymo(String mo) {
LocalModel city=repository.findBymo(mo);
return null;
}
}

Answer 1

In the service you are calling a function that doesn't exist in the repository layer. There is no method called findBymo in the repository. If LocalModel has a field called mo, you can just add a function in the repository interface like this
LocalModel findByMo(String mo);
and it will be implemented automatically.
If LocalModel doesn't have such field you should implement the query yourself in the repository like this
#Query("select ... query here")
LocalModel findByMo(String mo);