use morphia filter

service/src/main/java/com/telephoners/krakyournet/ctf/repositories/SolutionsRepository.java

@@ -46,22 +46,10 @@ public class SolutionsRepository extends Repository<Solution>
                 ));
     }
 
-    //todo: use datastore filter
     public boolean exists(Solution solution)
     {
-        //todo: refactor, ugly ;(
-        String value = solution.getFlag().getValue();
-        Optional<Solution> matchedSolution = getAll().stream()
-                .filter(new Predicate<Solution>()
-                {
-                    @Override
-                    public boolean test(Solution solution)
-                    {
-                        //todo: compare flags, not flag values
-                        return solution.getFlag().getValue().equals(value);
-                    }
-                })
-                .findFirst();
-        return matchedSolution.isPresent();
+        return datastore.find(Solution.class)
+                .filter("flag.value", solution.getFlag().getValue())
+                .get() != null;
     }
 }
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