Database updates

- In the local query examples,…the purchases for a property of the Customer class.…I want to form a similar relationship here…between the tables.…Since both tables have a last name property…for each customer, I could perform a joint query…to combine them by matching the last name in each table.…But linked to SQL has some additional functionality…to define this relationship in the class definition…to make this a little easier.…To set that up, I'll introduce an EntitySet…in the Customer class which acts like a where query…to find the associate data.…

Here, I'm specifying that the associated entity…is the purchase entity and in my customer constructor,…I'll have access to the purchase entity.…I'll also add an association attribute,…which gives LINQ to SQL information…on how the two entities and tables are related.…In our example, I'm specifying that the customer entity…is associated with the purchases entity…and the two map to one another using the key CLast.…And finally, I'll add to the Purchase property…to our class.…