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Defining a Foreign Key Property

2:59 with James Churchill

Let's see how we can require each comic book to be associated with a series by explicitly adding a foreign key property to the ComicBook entity class.

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/v3.3 -b defining-foreign-key-property

Foreign Key Property Name Conventions

When generating the in-memory entity data model, EF will will attempt to identify foreign key properties by checking if any of the entity's properties following these naming conventions:

  • {Navigation Property Name}{Principal Primary Key Property Name}
  • {Principal Class Name}{Primary Key Property Name}
  • {Principal Primary Key Property Name}

Let's take another look at the Series_Id foreign key column that 0:00
EF added to the Comic Books table. 0:04
We can see here, that the Series_Id column allows no values. 0:08
For our requirements, we want each comic book to be associated with the series, 0:12
so we need to tell EF to make this column not allow no values. 0:17
To accomplish this, 0:29
we can explicitly add a foreign key property to the comic book entity class. 0:30
SeriesId by following the naming convention of navigation 0:37
property name plus principal primary key property name, 0:43
EF will detect and interpret this property as a foreign key property. 0:47
Furthermore, because we're using a non nullable data type, 0:55
the foreign key table column will not allow nulls. 0:59
If we had a reason to not follow EF standard conventions, 1:02
we can name the foreign key property whatever we like. 1:06
And use the foreign key attribute to associate our foreign key property 1:09
with our navigation property. 1:13
Let's change the foreign key property name. 1:15
And add the foreign key attribute to the series navigation property. 1:19
ForeignKey, then add the using directive for 1:28
the System.ComponentModel.DataAnnotations.Sc- 1:32
hema namespace. 1:36
And pass in the name of the ForeignKey property, SeriesRefId. 1:37
Whenever possible, try to follow EF's conventions. 1:45
Doing so, will make your code cleaner and easier to follow. 1:48
That being said, if you're working with an existing database, 1:51
you'll likely need to stick with the column naming convention that has already 1:55
been established in the database. 1:59
When explicitly defining a foreign key property, I like to place it amongst my 2:03
other properties in the order that makes the most sense. 2:07
And place the navigation property just below my other properties. 2:11
I find that organizing my entity class code this way 2:15
helps me to quickly identify the navigation properties. 2:18
Another advantage of having an explicit foreign key property on our entity, 2:22
is that we can now associate a comic book with a series 2:27
by just setting the SeriesId property value. 2:30
We'll see an example of this later in this course. 2:33
Let's run our app one more time and 2:36
verify that the comic books' SeriesId column is added and configured correctly. 2:39
And here's our new SeriesId column which no longer allows null values. 2:53

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