Practical .NET

Defining Columns, Primary, and Composite Keys in Entity Framework

There are two attributes you can put on your entity class properties: one is a convenience, the other is essential, and both are required when the primary key for a table consists of two columns.

When creating an entity Class to work with one of your tables in your Entity Framework model, you might find the Column attribute useful. For one purpose, it's a convenience: If you have a column called txtFirstName (because it follows some naming convention used by the database design team) and you'd prefer to have your property just called FirstName (because that's your coding convention), then the Column attribute will let you have the property name you want. Just decorate the property in your entity Class with the Column attribute to tie your FirstName property to your txtFirstName column, like this:

Public Class Customer
    <Column(Name := "txtFirstName")>
   Public Property FirstName() As String

And that's nice to have.

While used like this, the Column attribute is a convenience, the Key attribute is required -- you have to use it to tell Entity Framework which of your columns corresponds to your table's primary key. This example tells Entity Framework that the Id property is the primary key column for the table:

Public Class Customer
   <Key()>
   Public Property Id() As Boolean
   <Column(Name := "txtFirstName")>
   Public Property FirstName() As String

But what if the primary key for your table has two (or more) columns? It's not enough just to flag the columns using Key -- you also have to specify the order of the columns in the key. You'll need to use both the Key and the Column attributes to do that. This example:

Public Class Customer
   <Key>
   <Column(Order := 1)>
   Public Property FirstName As String
   <Key>
   <Column(Order := 2)>
   Public Property LastName As String

specifies that the Customer table has a composite key of FirstName and LastName with FirstName coming first.

About the Author

Peter Vogel is a system architect and principal in PH&V Information Services. PH&V provides full-stack consulting from UX design through object modeling to database design. Peter tweets about his VSM columns with the hashtag #vogelarticles. His blog posts on user experience design can be found at http://blog.learningtree.com/tag/ui/.

comments powered by Disqus

Featured

  • Visual Studio 'Tea & Technology' Video Miniseries Starts Next Week

    The goal of the miniseries is to provide an insider's snapshot look at some of the people who contribute to shaping the Visual Studio IDE every day.

  • Microsoft Releases OpenJDK 21 Build for Java Jockeys

    Microsoft today announced its "Microsoft Build of OpenJDK 21," taking advantage of new features and functionality in Java 21.

  • 'Dev Home' Update Leads Developer Goodies in AI-Powered Windows 11 Update

    Along with today's new AI-powered Windows 11 update come new goodies for developers, including a new edition of Dev Home, a preview offering described as a "control center" providing coding-focused features and functionality.

  • Community Dev Gives VS Code Python Some YAPF

    The latest update to Python in Visual Studio Code includes a new extension for Python formatting that was contributed by a member of the open source community.

Subscribe on YouTube