EF Core 6 EntityTypeConfiguration Attribute

Daily Knowledge Drop

A new attribute called EntityTypeConfiguration was introduced in Entity Framework 6, which allows for easier configuration of custom entity configurations.

Let's take a look at how is simplifies the configuration of an entity.

Configurations previously

There are a number of steps performed when manually configuring an entity using Entity Framework Core (EF).

Note: The entity structure below is not optimized or suitable for a production system, it is used just for sample purposes

Define the entity

In this example, we are going to be using a Song entity.

This is straight forward and nothing EF related here.

public class Song
{
    public int Id { get; set; }

    public string Name { get; set; }

    public string Artist { get; set; }

    public int YearReleased { get; set; }

    public int LengthInSeconds { get; set; }
}

Add the DbSet

The next step is to make EF aware of this entity. We do this by creating a Dbset (using the entity) on the DbContext:

public class EntityTypeConfigContext : DbContext
{
    // This links the entity to EF
    public DbSet<Song> Songs { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(
            @"Server=.\SQLEXPRESS;Database=EntityTypeConfig;Integrated Security=True");
    }
}

Customize entity configuration

The next step is to create a configuration for the entity.

The default SQL column size for strings is nvarchar(max) - the below configuration changes this to 250 chars for the entity, for example.

public class SongConfiguration : IEntityTypeConfiguration<Song>
{
    public void Configure(EntityTypeBuilder<Song> builder)
    {
        builder.HasIndex(p => p.Id, "Id");
        builder.Property(p => p.Name).HasMaxLength(250);
        builder.Property(p => p.Artist).HasMaxLength(250);
    }
}

Apply the configuration

The final step is to apply the configuration to the DbContext:

public class EntityTypeConfigContext : DbContext
{
    public DbSet<Song> Songs { get; set; }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // when the model is creating, specify
        // the configuration should be used
        modelBuilder.ApplyConfiguration(new SongConfiguration());
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(
            @"Server=.\SQLEXPRESS;Database=EntityTypeConfig;Integrated Security=True");
    }
}

EntityTypeConfiguration attribute

The above 4 steps will still work with EF Core 6, however the last step can now be simplified.

Instead of manually adding each entity configuration to the OnModelCreating method on the context, the entity itself can be tagged with the EntityTypeConfiguration attribute.

// This attribute will ensure the "SongConfiguration" is used 
// when configuring the "Song" entity in EF
[EntityTypeConfiguration(typeof(SongConfiguration))]
public class Song
{
    public int Id { get; set; }

    public string Name { get; set; }

    public string Artist { get; set; }

    public int YearReleased { get; set; }

    public int LengthInSeconds { get; set; }
}

The SongConfiguration configuration will now automatically be used for the Song entity by the EF when creating the database model.

Notes

While using the EntityTypeConfiguration attribute is cleaner and easier, and probably likely less to be overlooked by the developer, the technique will not work for everyone. Depending on the application design/architecture it might not make sense to "pollute" the entity wth any EF specific references.

What is important though, is that there are now multiple options to leverage depending on what sense for your specific use case.

References

Entity Framework Core 6 features - Part 1

Daily Drop 15: 21-02-2022

At the start of 2022 I set myself the goal of learning one new coding related piece of knowledge a day.
It could be anything - some.NET / C# functionality I wasn't aware of, a design practice, a cool new coding technique, or just something I find interesting. It could be something I knew at one point but had forgotten, or something completely new, which I may or may never actually use.

The Daily Drop is a record of these pieces of knowledge - writing about and summarizing them helps re-enforce the information for myself, as well as potentially helps others learn something new as well.