ASP.NET MVC 4, EF5, Unique property in model - best practice?

Question

ASP.NET MVC 4, EF5, Code First, SQL Server 2012 Express

What is best practice to enforce a unique value in a model? I have a places class that has a

Answer 1

The only way is to update your migration once you generate it, assuming you are using them, so that it enforces a unique constraint on the column.

public override void Up() {
  // create table
  CreateTable("dbo.MyTable", ...;
  Sql("ALTER TABLE MyTable ADD CONSTRAINT U_MyUniqueColumn UNIQUE(MyUniqueColumn)");
}
public override void Down() {
  Sql("ALTER TABLE MyTable DROP CONSTRAINT U_MyUniqueColumn");
}

The hard bit, though, is enforcing the constraint at the code level before you get to the database. For that you might need a repository that contains the complete list of unique values and makes sure that new entities don't violate that through a factory method.

// Repository for illustration only
public class Repo {
  SortedList uniqueKey1 = ...; // assuming a unique string column 
  public Entity1 NewEntity1(string keyValue) {
    if (uniqueKey1.ContainsKey(keyValue) throw new ArgumentException ... ;
    return new Entity1 { MyUniqueKeyValue = keyValue };
  }
}

References:

• Repository - Fowler (the original source of Repository)
• Repostory - MSDN
• Tutorial: Repository in MVC (www.asp.net)
• Singleton in C# - SO

Footnote:

There are a lot of requests for [Unique] in code first, but it looks like it isn't even making version 6: http://entityframework.codeplex.com/wikipage?title=Roadmap

You could try voting for it here: http://data.uservoice.com/forums/72025-entity-framework-feature-suggestions/suggestions/1050579-unique-constraint-i-e-candidate-key-support