Author: Craig Stuntz

In Code First Entity Framework models, you can define the length of a string field with StringLengthAttribute, but you have to write code in OnModelCreating to indicate a CHAR/NCHAR fixed length field:

public class MyEntity

{

	[Key]

	public int Id { get; set; }



	[StringLength(2)]

	public string FixedLengthColumn { get; set; }

}



public partial class MyContext : DbContext

{

	public virtual DbSet MyEntities { get; set; }



	protected override void OnModelCreating(DbModelBuilder modelBuilder)

	{

		if (modelBuilder == null) throw new ArgumentNullException("modelBuilder");



		modelBuilder.Entity()

			.Property(e => e.FixedLengthColumn)

			.IsFixedLength();

	}

}

I find it a bit confusing to split configuration like this, especially with a real model containing lots of fields and not this trivial example. Fortunately, you can fix it! Add these:

/// <summary>

/// Used to mark entity properties that are fixed length strings (CHAR(n) DB fields).

/// </summary>

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false, Inherited = true)]

public sealed class FixedLengthAttribute : Attribute {}



public class FixedLengthAttributeConvention :  PrimitivePropertyAttributeConfigurationConvention

{

	public override void Apply(ConventionPrimitivePropertyConfiguration configuration, FixedLengthAttribute attribute)

	{

		configuration.IsFixedLength();

	}

}

And change the model configuration to:

public class MyEntity

{

	[Key]

	public int Id { get; set; }



	[StringLength(2),

	 FixedLength]

	public string FixedLengthColumn { get; set; }

}



public partial class MyContext : DbContext

{

	public virtual DbSet MyEntities { get; set; }



	protected override void OnModelCreating(DbModelBuilder modelBuilder)

	{

		if (modelBuilder == null) throw new ArgumentNullException("modelBuilder");



		modelBuilder.Conventions.Add<FixedLengthAttributeConvention>();

	}

}

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