Code-First Development with Entity Framework 4
page 8 of 21
by Scott Guthrie
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Code Examples of How to Use Our Model

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:

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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:

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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:

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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.

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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:

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