Question

I have 2 entities: Train and Station

Each train stops at multiple stations, i.e. Train <--->> Station.
The list of stations a train stops at is different from the list of stations some other train stops at.

How do I correctly save and fetch the list of stations for a particular train?

Thanks

Answer 1

Does this:

Train <--->> Station

mean you have a one to many relationship? If so, it doesn’t work, unless only one train can stop at each station. What I would do is create a third entity, call it say “stop” with two relations, a many to one to Train and a many to one to Station. It wil look something like

+-----+       +-------+
|Train|       |Stop   |        +-------+
+-----+       +-------+        |Station|
|stops|<---->>|train  |        +-------+
+-----+       |station|<<----->|stops  |
              +-------+        +-------+

To find all the stations a particular train stops at, just look at the stops property of the Train which will be an NSSet of Stop objects each of which has a property which is a station the train stops at.

To add new stops, just create a new Stop object and set its train and station properties appropriately.