Migrating to v18.0.0

CsvHelper 18 lets you map constructor parameters. A type without a parameterless constructor is created with its constructor, and each parameter is read from the column with the parameter's name. Now you can give a parameter another column name or an index, with [Name] and [Index] on the parameter or with Parameter in a class map. Nothing was removed or renamed: NameAttribute and IndexAttribute implement a new interface, IParameterMapper, and can be put on parameters.

Constructor parameters

Put [Name] or [Index] on the parameter:

public class Foo
{
    public Foo([Name("Foo Id")] int id, [Name("Foo Name")] string name)
    {
        Id = id;
        Name = name;
    }

    public int Id { get; }

    public string Name { get; }
}

using var csv = new CsvReader(reader, CultureInfo.InvariantCulture);
var records = csv.GetRecords<Foo>().ToList();

Or map the parameters in a class map, with Parameter and the parameter's name:

public class Foo
{
    public Foo(int id, string name)
    {
        Id = id;
        Name = name;
    }

    public int Id { get; }

    public string Name { get; }
}

public class FooMap : ClassMap<Foo>
{
    public FooMap()
    {
        Parameter("id").Name("Foo Id");
        Parameter("name").Name("Foo Name");
    }
}

using var csv = new CsvReader(reader, CultureInfo.InvariantCulture);
csv.Configuration.RegisterClassMap<FooMap>();
var records = csv.GetRecords<Foo>().ToList();

• Map every parameter, in order. The constructor is called with the parameters of the map, in the order of the Parameter calls.
• Which constructor: Parameter(name) looks for the parameter in the constructor with the most parameters, the one records are created with by default. Parameter(() => constructor, name) and Parameter(constructor, parameter) take another; set the configuration's GetConstructor to create records with it.
• Name or index: a parameter is read by its name when you set one, or when the file has a header and you didn't set an index; otherwise by its index. A parameter with only an index isn't checked by header validation.
• Registering: a class map with only Parameter maps can be registered; 17 threw "No mappings were specified".