ASP .NET CORE Backing Fields

When a backing field is configured, EF will write directly to that field when materializing entity instances from the database (rather than using the property setter). If EF needs to read or write the value at other times, it will use the property if possible. For example, if EF needs to update the value for a property, it will use the property setter if one is defined. If the property is read-only, then it will write to the field.

class MyContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Blog>()
            .Property(b => b.Url)
            .HasField("_validatedUrl");
    }
}

public class Blog
{
    private string _validatedUrl;

    public int BlogId { get; set; }

    public string Url
    {
        get { return _validatedUrl; }
    }

    public void SetUrl(string url)
    {
        using (var client = new HttpClient())
        {
            var response = client.GetAsync(url).Result;
            response.EnsureSuccessStatusCode();
        }

        _validatedUrl = url;
    }
}

Controlling when the field is used

modelBuilder.Entity<Blog>()
    .Property(b => b.Url)
    .HasField("_validatedUrl")
    .UsePropertyAccessMode(PropertyAccessMode.Field);