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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}
  • 0:00

    Let's take another look at the Series_Id foreign key column that

  • 0:04

    EF added to the Comic Books table.

  • 0:08

    We can see here, that the Series_Id column allows no values.

  • 0:12

    For our requirements, we want each comic book to be associated with the series,

  • 0:17

    so we need to tell EF to make this column not allow no values.

  • 0:29

    To accomplish this,

  • 0:30

    we can explicitly add a foreign key property to the comic book entity class.

  • 0:37

    SeriesId by following the naming convention of navigation

  • 0:43

    property name plus principal primary key property name,

  • 0:47

    EF will detect and interpret this property as a foreign key property.

  • 0:55

    Furthermore, because we're using a non nullable data type,

  • 0:59

    the foreign key table column will not allow nulls.

  • 1:02

    If we had a reason to not follow EF standard conventions,

  • 1:06

    we can name the foreign key property whatever we like.

  • 1:09

    And use the foreign key attribute to associate our foreign key property

  • 1:13

    with our navigation property.

  • 1:15

    Let's change the foreign key property name.

  • 1:19

    And add the foreign key attribute to the series navigation property.

  • 1:28

    ForeignKey, then add the using directive for

  • 1:32

    the System.ComponentModel.DataAnnotations.Sc-

  • 1:36

    hema namespace.

  • 1:37

    And pass in the name of the ForeignKey property, SeriesRefId.

  • 1:45

    Whenever possible, try to follow EF's conventions.

  • 1:48

    Doing so, will make your code cleaner and easier to follow.

  • 1:51

    That being said, if you're working with an existing database,

  • 1:55

    you'll likely need to stick with the column naming convention that has already

  • 1:59

    been established in the database.

  • 2:03

    When explicitly defining a foreign key property, I like to place it amongst my

  • 2:07

    other properties in the order that makes the most sense.

  • 2:11

    And place the navigation property just below my other properties.

  • 2:15

    I find that organizing my entity class code this way

  • 2:18

    helps me to quickly identify the navigation properties.

  • 2:22

    Another advantage of having an explicit foreign key property on our entity,

  • 2:27

    is that we can now associate a comic book with a series

  • 2:30

    by just setting the SeriesId property value.

  • 2:33

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

  • 2:36

    Let's run our app one more time and

  • 2:39

    verify that the comic books' SeriesId column is added and configured correctly.

  • 2:53

    And here's our new SeriesId column which no longer allows null values.

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