Spring JPA自定义查询返回JSON

Question

I am using Spring hibernate with JPA Repository to return the values as JSON. It works fine for all default cases. I am having a problem with custom query in my CrudRepository to return aggregated values as JSON.

CrudRepository

@Repository
public interface ExpenseRepository extends CrudRepository<Expense, Integer>{
    @Query("SELECT min(dtDate) as dtDate ,Max(dtDate) as dtDate FROM Expense")
    Iterable<Expense> getAvlRptDates();
}

NOTE: I have tried with and without Alias, List etc as well.

Controller

@ResponseBody
@RequestMapping(value="/getAvlExpMonthYear",method=RequestMethod.GET)
public Iterable<Expense> getAvlRptDates(){
    //String test = testRepo.findAll().toString();
    return expRepo.getAvlRptDates();
}

I tried with List as well. I know that converting to JSON with custom code or additional dto classes.

Please let me know if there any easy way without creating additional domain class or dto classes just for two fields.

Answer 1

Change this:

@Repository
public interface ExpenseRepository extends CrudRepository<Expense, Integer>{
    @Query("SELECT min(dtDate) as dtDate ,Max(dtDate) as dtDate FROM Expense")
    Iterable<Expense> getAvlRptDates();
}

To the following changing Iterable to Optional which returns a list of Jsons:

@Repository
public interface ExpenseRepository extends CrudRepository<Expense, Integer>{
    @Query("SELECT min(dtDate) as dtDate ,Max(dtDate) as dtDate FROM Expense")
    Optional<Expense> getAvlRptDates();
}

Now, you will get some sort of JSON but not the kind of json that meets official standards.

So my recommendation is to do:

@Repository
public interface ExpenseRepository extends CrudRepository<Expense, Integer>{
    @Query("SELECT min(dtDate) as dtDate ,Max(dtDate) as dtDate FROM Expense")
    Expense[] getAvlRptDates();
}

Where it return a single iterable, then convert the contents of the iterable to json one by one. See below link:

How to convert list data into json in java

Hope it helps.