Associate a user with an abstract class implementation based on their role
Let's suppose that we have a User class that is necessarily associated with a Role, which can be DogLover or CatLover.
We have another abstract class called Animal, which has two implementations, Dog and Cat.
The User has an attribute called pet that will be a Cat or a Dog, depending on the Role chosen.
How can I show this on the diagram?
I cannot relate the implementation of each Animal with the Role since the animal must be associated with the user
In this design Role and Animal are covariant, because the Role specialisation express love for corresponding Animal specialisations. There is unfortunately no easy way to model this.
One way of designing this is to use pet:Animal and model it with an association. You have then two options:
- simply define a constraint for
User, that would require the pet type and the role type match. To facilitate this design, I'd even consider making the role's specialisation a template class, i.e.Lover<T:Animal> - or make the role association a derived association (its name should be preceded with
/). The derivation would be based on the real type of the pet. SO if the pet changes, the derivation could change as well.
A better way to design this would be to move the pet from the User to the Role. The user has no animal, but in his/her role of DogLover he/she could have Dog (or CatLover a Cat). You can then use association specialization to clearly show the covariance. Several techniques can be used for this purpose as shown in the answers to this other question, for example:
This being said, in the real life, DogLover and CatLover are not necessarily incompatible, and one could even have a Dog for historical reasons while being a CatLover. Separating the concerns of ownership and preference, would be an even better design.
- Checking if Type or instance implements IEnumerable regardless of Type T
- Base class method working on private member of derived class
- C++ template class inheritance: calling base class constructor in derived class constructor
- c++ Linker error undefined reference to vtable
- How can you inherit from a sealed class using reflection in .Net?
- AttributeError: object has no attribute 'method'
- Implicit casting / polymorphism with a Dictionary in C#
- Why is the __proto__ of Object.prototype, another Object.prototype?
- why derive from a concrete class is a poor design
- Inheritance classes in Scheme
- How to "perfectly" override a dict?
- Inherited javascript property not set during constructor
- Template inference when there are multiple possibilities?
- Derived python dataclass cannot override default value?
- How to print the string name of a class that inherits attributes and methods from a parent class
- Why can't I make an abstract method static in my implementation?
- Dataclass inheriting using kw_only for all variables
- Dataclass inheritance variables not working
- How to let two Python abstract classes implement each other's abstract methods?
- Typescript Extend Generic Interface
- How do I assign the derived class name as a param within the base class constructor?
- C# - Making all derived classes call the base class constructor
- Visual Inheritance - Add controls at designer to a Panel hosted in TableLayoutPanel
- Java inheritance vs initialization
- Can CSS detect the difference between an actual hover and an inherited hover?
- What is the C++ equivalent of inheriting a Java collection interface (Set, Map, List etc.)? Or extending AbstractCollection?
- derived class cannot call its own method?
- How to handle inheritance in mypy?
- Define a common interface without dynamic polymorphism
- Java object-oriented understanding problem