How to model a Many to many-relationship in code?

Question

Suppose I have 2 tables in a database. eg: Dog & Boss This is a many to many relationship, cause a boss can have more than 1 dog, and a dog can have more than 1 owner. I

Answer 1

Every time we need to think about real life and our needs. In this case, the key point is which one should have another one.

In real life a dog and a boss may dont have each other. But your software needs should effect this relationship.

• For example if you are developing a veterinarian patient management software, for a veterinarian who cures stray dogs then Patient(dog)-Guardian(boss) relationship should be like this : Bosses must have at least one dog and dog may dont have any boss(then boss id is the foreign key of this relationship) that means in your design the dog class must hold a collection of bosses. Why because any boss instance can not be created without any dog(s). We can get this decision with the the data logic too. Lets think about when you are trying to save your dog and boss classes in database. If the relation condition like above, while saving a boss you should insert a junction record into the junction table.

• If you are developing that software a veterinarian who dont cures stray dogs, then Patient - Parent relationship needs to be like this: A dog must have at least one boss and boss must have at least a dog, and we need to consider this special relationship case. That means any of these classes instances can not be created without eachother. So we need to define this speciality in our OO design. That means we need a class which represents this dependency. Ofcourse this dependency will stored in junction table.

-If your software developed for a veterinarian who cures stray dogs and these dogs adopted by bosses your design should be like this: Any dog may dont have boss(es) and any boss may dont have any dog(s) until adoption. In this case our OO design needs to care about this special case. This case a little bit same as the first one. So we can add collection of any class into other one. But, any software needs like this will effect other needs. Like reporting. If veterinarian concerns about dogs which adopted by boss(es), sooner or later he asks a report which dog adopted by who. Like in the sentence, (dogs adopted by boss(es)) it is better if dog class contains a collection of boss classes.

I hope I can give proper answers to your question.