The three classes we created earlier contain all of the code necessary to implement our model and data persistence for NerdDinner.  Let’s now look at a few code examples of how we can use these classes to perform common data scenarios:

Query Using LINQ Expressions

We can write LINQ query expressions to retrieve data from a database using the following code.  Below we are using a LINQ expression to retrieve all dinners that occur in the future:

We can also take advantage of relationships between Dinners and RSVPs when writing our LINQ expressions.  Notice below how our “where” statement filters by dinners whose RSVP count is greater than 0:

Note that the “where” filter in the above query (where we are retrieving only those Dinners who have at least one RSVP) executes in the database server – making the query and the amount of data we retrieve very efficient.

Retrieving a Single Instance

We can use LINQ’s Single() method with a lambda query to retrieve a single instance of a Dinner using code like below:

Alternatively, we can also take advantage of a Find() method that EF “code-first” exposes that allows you to easily retrieve an instance based on its ID:

Adding a new Dinner

The code below demonstrates how to create and add a new Dinner to the database.  All we need to do is to “new” a Dinner object, set properties on it, and then add it to the Dinners property of our NerdDinners context object.  The NerdDinner context class supports a “unit of work” pattern that enables you to add multiple models to the context, and then call “SaveChanges()” on it to persist all of the changes to a database as a single atomic transaction.

Updating a Dinner

The code below demonstrates how to retrieve a Dinner, update one of its properties, and then save the changes back to the database: