How To Setup Core Data Model For Simple App?

I'm familiar with core data but want to make a simple app that calculates salary. User enters their expenses, etc and it will determine how much their income needs to be to make it work.

I'm thinking I make an entity for each Event and then have an attribute expens开发者_开发问答e for each expense.

Is there then an easy way to add all these values of expense properties and do some calculations with them? I will set their type to float or nsnumber or int, etc.

Update: I will make the relationship of Event to Expense to many and the inverse relation ship would be one to one. But about actually doing calculations with these values?

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If you are going to add many values to Entity, you must use a relationship between them, it's the only way to have and Event with its Expenses...

Event <---->> Expense

An Event has too many Expenses and every Expense belongs to an Event...