added username for uniqueness of connection db entry

backend/src/main/java/com/vaessl/app/connection/ConnectionEntity.java

@@ -8,12 +8,13 @@ import jakarta.persistence.Id;
 import jakarta.persistence.Inheritance;
 import jakarta.persistence.InheritanceType;
 import jakarta.persistence.Table;
+import jakarta.persistence.UniqueConstraint;
 import lombok.Getter;
 import lombok.NoArgsConstructor;
 import lombok.Setter;
 
 @Entity
-@Table(name = "connections")
+@Table(name = "connections", uniqueConstraints = { @UniqueConstraint(columnNames = { "appUrl", "username" }) })
 @Inheritance(strategy = InheritanceType.SINGLE_TABLE)
 @DiscriminatorColumn(name = "service_type")
 @Getter
@@ -23,6 +24,7 @@ public abstract class ConnectionEntity {
     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     private Long id;
-    
+
     private String appUrl;
+    private String username;
 }