What makes O/R mappers like LINQ to SQL extremely flexible
is that they enable us to easily model cross-table relationships across our
data model. For example, I can model each Product to be in a Category,
each Order to contain OrderDetails for line-items, associate each OrderDetail
line-item with a Product, and have each Customer contain an associated set of
Orders. I covered how to construct and model these relationships in Part 2 of this blog series.
LINQ to SQL enables me to take advantage of these
relationships for both querying and updating my data. For example, I could
write the below code to create a new Product and associate it with an existing
"Beverages" category in my database like so:
Figure 8
Note above how I'm adding the Product object
into the Category's Products collection. This will indicate that there is
a relationship between the two objects, and cause LINQ to SQL to automatically
maintain the foreign-key/primary key relationship between the two when I call
"SubmitChanges()".
For another example of how LINQ to SQL
can help manage cross-table relationships for us and help clean up
our code, let's look at an example below where I'm creating a new Order for an
existing customer. After setting the required ship date and freight costs
for the order, I then create two order line-item objects that point to the
products the customer is ordering. I then associate the order with the
customer, and update the database with all of the changes.
Figure 9
As you can see, the programming model for performing all of
this work is extremely clean and object oriented.
