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Let's add a context class to our project, so we can persist and retrieve data from our database.
Follow Along
To follow along commiting your changes to this course, you'll need to fork the dotnet-comic-book-gallery-model repo. Then you can clone, commit, and push your changes to your fork like this:
git clone <your-fork>
cd dotnet-comic-book-gallery-model
git checkout tags/v1.6 -b adding-our-context
Additional Learning
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.
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