Similar Classes......Or are they the same? 2

[Craig0201]

Hi,

Best to explain this by analogy.....

Imagine a 100 Metre track and field race.

A race contains a number of runners each of which produces a performance.

A runner has a number a performances over a number of races.

Races and runners therefore both contain the collection object Performances. But for each performance within a race context, I need to know the runner ID, not the race ID (contained in Race) and for each performance in a runner object I need to know the race ID, not the runner ID (contained in race)

Now I know that I could create a generic Performance class and inherit it and add the property I need in a further 2 classes. But this seems intuitively wrong.

I'm sure there is a better way of doing this. Can anyone help, please?

Craig

 

[mikewoodhouse]

In data modelling terms, Performance would be an entity that represents the linkage between runners and races (a 'many-to-many' relationship). Once implemented as a table, this gives you a single source for "all races for a runner" and "all runners for a race".

Taking a simple approach, why not just implement that relationship as a class, so you have one class with runner and race ids. There's probably a pattern for this, but I can't think of it (too early!)

HTH,

Mike

 

[Craig0201]

Mike,

Thought of that. That doesn't seem right to me either. DBwise, agreed but it doesn't seem to fit with OO.

But much appreciated comment!

Craig

 

[Craig0201]

Mike,

Mention of patterns had me rooting around. Do you think this fits with Mediator?

Craig

 

[mikewoodhouse]

So you'd have a class that delivered, say

RunnersFor(Race) and Racesfor(Runner)

methods?

 

[Craig0201]

As I thought....my thought was gibberish!

How about describing an interface with the two methods and having the classes implement that interface and inherit from the superclass?

Craig

 

[DonQuichote]

I agree with mikewoodhouse. In fact, to identify a performance you need both the runner and the race.

If you are using persistent objects, I can imagine that you have a

Performances

collection that handles the persistence.
Your

Runner

object would then have a

performanceForRace

method (delegating to the

Performances

collection, passing itself as the runner) and a

Race

object would have a

performanceForRunner

method.
If there is not a performance for each race and/or runner, both the

Runner

and the

Race

would have a

performances

collection with the

performances

that do exist.

Hope this helps or amuses

 

[Craig0201]

Don/Mike,

Convinced.

Thanks for the help.

Craig