Question

In my application, I have two classes: Activity and User. The relationship among them are:

• An activity can have multiple user. I have a field List<User> for this purpose in Activity class.
• An user can belongs to multiple activities and in each activity he/she can have a specific role. I have refined a Map<String, String> in User, where the key of this Map is the activityId and the value is roleId. I don’t have any Role table, as there are only four predefined Roles.

I am unable to understand should there be any ManyToOne or OneToMany or ManyToMany relationship between User and Activity. Or should I simple store the whole List<User> object along with Activity and Map<String, String> with User in database. If so, how can I store a whole List and a Map.

Any pointer would be very helpful for me.

Answer 1

I would first think about how the design would be in database. If I understand correctly, you would have 3 tables:

• User
• Activity
• Participation

where Participation would have a foreign key to a user, a foreign key to an activity, and a role.

So I would map that simply as

• User has a OneToMany with Participation
• Activity has a OneToMany with Participation

And of course you can make these two associations bidirectional.