I decided to use single table inheritance which results in having multiple classes and I can't access the child's fields through a parent object in the view part of the application. So far I didn't find a nice solution how to deal with it in Thymeleaf. What does it mean?
Before I split my classes to use single table inheritance I could easily pass 1 object class that contained all the information needed to create or display the object but it had too many fields that would be null. With multiple classes thymeleaf doesn't really allow you to cast objects to a different type(and from what I understand it wouldn't be a good practice to do that in a view part of the application). So what is really the best way to deal with this problem?
I can come up with ideas like:
- Create a DTO that contains the fields from all the classes and transform the objects to this class, it would be great in a create-view (POSTing DTO and then creating an object from it and adding to the database). But if I used this method for displaying information then it would mean casting each of the objects to a DTO class which kind of misses the point of single table inheritance in my opinion. I feel like this is too similar to going back to no inheritance at all.
- Passing multiple objects or a parent object + a different object that would hold the rest of the information that the parent class doesn't hold. This also seems kind of weird.
- Adding one method to a parent class per sub-class additional field and overwrite them in the sub-classes to return actual values while parent would return null. Not sure if this would fix the problem of creating the objects from a view though.
Let's assume this example with three simple classes where Person is a parent class and Client and Employee are children of it. I will skip getters, setters and constructors for simplicity.
Person main class that holds shared fields
@Entity
@Inheritance
@DiscriminatorColumn(name = "person_type", discriminatorType = DiscriminatorType.STRING)
public abstract class Person {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
int personId;
int age;
String name;
}
Client class that extends person with additional field favouriteProduct
@Entity
@DiscriminatorValue(value= "CLIENT")
public class Client extends Person {
String favouriteProduct;
}
Employee class that extends person with additional fields salary and position.
@Entity
@DiscriminatorValue(value= "EMPLOYEE")
public class Employee extends Person {
String position;
int salary;
}
Given this simple structure I would like to create Employee and Client objects through a single form via a POST request and also display them together in a different view with their fields that are unique to each subclass. Problem is that I would need to pass an object that holds all the fields to the view to actually make it work which comes back to the problem and solutions that I came up with. Is there any correct way or best practice how to deal with this? I thought DTOs should rather scale down from full objects to objects with less fields.
Conclusion: if the answer isn't really that simple then what is really the use of single table inheritance in this case and why isn't it a good idea to just go back to 1 table implementation? I already know about polymorphic queries and it is a nice bonus but so far I can't really deal with the problem I explained above. Thanks in advance!
