Migrating to v9.0.0

CsvHelper 9 is the changes of 8.2 and 8.3 under a new major version. Those two releases were unlisted on NuGet because 8.2 adds a member to the class map builder interfaces, which breaks code that implements them. If you don't implement those interfaces, your code compiles unchanged: 9 adds optional members to attributes and the class map builder, and allows a null character as the delimiter. The target frameworks don't change: .NET Standard 2.0 and .NET Framework 4.5.

Optional members

8.1 added Optional() to class maps: an optional member is skipped when reading if no field has its name, instead of failing header validation. 9 adds the same option as an attribute:

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

    [Optional]
    public string Notes { get; set; }
}

And to the class map builder, which Factory.CreateClassMapBuilder<T>() returns:

public class Order
{
    public int Id { get; set; }
    public string Notes { get; set; }
}

var map = new Factory().CreateClassMapBuilder<Order>()
    .Map(m => m.Id)
    .Map(m => m.Notes).Optional()
    .Build();

If you implement IHasMapOptions<TClass, TMember> yourself, it now extends IHasOptional<TClass, TMember>: add IHasOptionalOptions<TClass, TMember> Optional().

Behavior changes

• Null character delimiter: setting Delimiter to "\0" threw a ConfigurationException. It's allowed now.