Added some JPA optimizations

Author: Rajeev Kumar Singh

polling-app-server/src/main/java/com/example/polls/model/Choice.java

@@ -20,7 +20,7 @@ public class Choice {
     @Size(max = 40)
     private String text;
 
-    @ManyToOne(fetch = FetchType.LAZY)
+    @ManyToOne(fetch = FetchType.LAZY, optional = false)
     @JoinColumn(name = "poll_id", nullable = false)
     private Poll poll;
 

polling-app-server/src/main/java/com/example/polls/model/Vote.java

@@ -15,15 +15,15 @@ public class Vote extends DateAudit {
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     private Long id;
 
-    @ManyToOne(fetch = FetchType.LAZY)
+    @ManyToOne(fetch = FetchType.LAZY, optional = false)
     @JoinColumn(name = "poll_id", nullable = false)
     private Poll poll;
 
-    @ManyToOne(fetch = FetchType.LAZY)
+    @ManyToOne(fetch = FetchType.LAZY, optional = false)
     @JoinColumn(name = "choice_id", nullable = false)
     private Choice choice;
 
-    @ManyToOne(fetch = FetchType.LAZY)
+    @ManyToOne(fetch = FetchType.LAZY, optional = false)
     @JoinColumn(name = "user_id", nullable = false)
     private User user;