So I wanted a general enough way to get the id columns from my entities. This is either Paula Bean brilliant or glorious. I don't know which.

EntitySupport.cs

static class EntitySupport
{
  class IdentityGetter<TEntity>
	{
		public readonly static Func<TEntity,int> Instance = GetIdentityGetter<TEntity>(); 
	}
	
	public static Func<TEntity,int> GetIdentityGetter<TEntity>() 
	{
		var id = typeof(TEntity).GetMembers()
			.Select(member => new { member, column = (ColumnAttribute)member.GetCustomAttributes(typeof(ColumnAttribute), true).FirstOrDefault() })
			.SingleOrDefault(x => x.column != null && x.column.DbType == "Int NOT NULL IDENTITY");
		switch(id.member.MemberType) 
		{
			case MemberTypes.Property: return (Func<TEntity,int>)Delegate.CreateDelegate(typeof(Func<TEntity, int>), (id.member as PropertyInfo).GetGetMethod());
		}
		return _ => { throw new NotSupportedException(); };
	}
	
	public static int GetIdentity<TEntity>(TEntity entity) 
	{
		return IdentityGetter<TEntity>.Instance(entity);
	}
}