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Before we can persist and

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retrieve data from our database, we need
to add a context class to our project.

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The context class is our
gateway to the database.

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All communication from our application to
the database flows through the context.

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The context defines
the available Entity sets and

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manages the relationships
between those entities.

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It's used to retrieve entities
from the database, persist new and

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changed entities to the database, and
even to remove entities from the database.

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When retrieving entities from the
database, the context is responsible for

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materializing the data from the database
into Entity Object Instances.

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The context also caches those entity
object instances for its lifetime, however

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short or long that might be so that it
can track changes to those entities.

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As we learn about EF and
develop our projects,

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we'll interact with the context again and
again.

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Let's see how to add a context
class to our project.

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Right-click on the project and
select Add > Class.

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Name the class Context and click Add.

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Just like we did with the entity class, go
ahead and add the public access modifier.

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Then inherit from the EF DbContext class.

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Visual Studio will complain
that it can't find the type.

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So go ahead and
add the missing using statement for

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the System.Data.Entity namespace.

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The DbContext class is a higher level
abstraction of EF's object context class.

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before the DbContext
class was added to EF,

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object context was used to load and
persist entities.

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While object context isn't deprecated,

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it's almost never used directly now
that we have the DbContext class.

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Given that, we'll focus on learning
how to use the DbContext class.

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Our context class needs to contain
a collection of Db set properties.

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One property for each indie that
we need to write queries for.

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Let's add a Db set property for
the ComicBook entity.

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Public DbSet of type ComicBook.

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Add the missing namespace, or
ComicBookGalleryModel.Models, and

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use the plural version of our entity class
name for the property name, ComicBooks.

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While not necessary, using the plural
version of the entity class name

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is a common convention for
DB set property names.

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Often, you'll add a DB set property for

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each entity class that
you have in your model.

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But sometimes you won't need to add
a DB set property for an entity.

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We'll see an example of
that later in this course.

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For now, this is all of the code that
our context class needs to contain.

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Next, we'll update our
console app to persist and

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retrieve data using our context.