Unique keys in Entity Framework 4

by

The Entity Framework 6.1 now supports uniques with both Data Annotations and Fluent API.

Data Annotations (Reference)

public class MyEntityClass
{ 
    [Index(IsUnique = true)]
    [MaxLength(255)] // for code-first implementations
    public string MyUniqueProperty{ get; set; } 
}

Fluent API (Reference)

public class MyContext : DbContext
    {
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder 
                .Entity<MyEntityClass>() 
                .Property(t => t.MyUniqueProperty) 
                .HasMaxLength(255) // for code-first implementations
                .HasColumnAnnotation( 
                    "Index",  
                    new IndexAnnotation(new[] 
                        { 
                            new IndexAttribute("Index") { IsUnique = true } 
                        })));
        }
    }
}

You have to apply an index and set the unique property to true. By default, indexes are non-unique according to documentation.

And also you have to install the Entity Framework 6.1 NuGet package in your project in order to use the new API for indexes.

Note about code-first implementations: A VARCHAR(MAX) cannot be part of a unique constraint. You must specify the maximum length either as a Data Annotation or in the Fluent API.

More Related Contents:

  1. What’s the difference(s) between .ToList(), .AsEnumerable(), AsQueryable()?
  2. Unique Key constraints for multiple columns in Entity Framework
  3. Disable lazy loading by default in Entity Framework 4
  4. ADO.NET DbContext Generator vs. ADO.NET Poco Entity Generator (ObjectContext)
  5. How to include a child object’s child object in Entity Framework 5
  6. Entity Framework 4 / POCO – Where to start? [closed]
  7. Asp.Net Web API Error: The ‘ObjectContent`1’ type failed to serialize the response body for content type ‘application/xml; charset=utf-8’
  8. The specified named connection is either not found in the configuration, not intended to be used with the EntityClient provider, or not valid
  9. Entity Framework 4 selective lazy loading properties
  10. Upgrade EF 4 EDMX to EF 6
  11. Querying objects after AddObject before SaveChanges?
  12. EF Migrations: Rollback last applied migration?
  13. EF Code First giving me error Cannot insert explicit value for identity column in table ‘People’ when IDENTITY_INSERT is set to OFF. [duplicate]
  14. Using Entity Framework with an SQL Compact Private Installation
  15. Map two different entities to the same table?
  16. How to use Entity Framework to map results of a stored procedure to entity with differently named parameters
  17. AutomaticMigrationsEnabled false or true?
  18. Compose queries across Entity Data Models
  19. Changing Inherited Types in Entity Framework
  20. Convert String to Int in EF 4.0
  21. How to select top N rows for each group in a Entity Framework GroupBy with EF 3.1
  22. EF5 Code First Enums and Lookup Tables
  23. How can I delete 1,000 rows with EF6?
  24. Entity Framework 4.2 exec sp_executesql does not use indexes (parameter sniffing)
  25. Multi-async in Entity Framework 6?
  26. SQL Server Express connection string for Entity Framework Code First
  27. EF Code First DBContext and Transactions
  28. EF Code First foreign key without navigation property
  29. LINQ to Entities for subtracting 2 dates
  30. Why does the entity framework need an ICollection for lazy loading?

Leave a Comment