Collections

Facette handles collection properties automatically, mapping each element using the nested DTO's FromSource/ToSource methods.

Supported collection types

The generator recognizes and handles these collection types:

• List<T>
• T[] (arrays)
• IList<T>, ICollection<T>, IEnumerable<T>, IReadOnlyList<T>, IReadOnlyCollection<T>
• HashSet<T>, ISet<T>
• ImmutableArray<T>, ImmutableList<T>

Example

public class Order
{
    public int Id { get; set; }
    public string CustomerName { get; set; } = "";
    public List<OrderItem> Items { get; set; } = new();
}

public class OrderItem
{
    public string ProductName { get; set; } = "";
    public decimal UnitPrice { get; set; }
    public int Quantity { get; set; }
}

[Facette(typeof(OrderItem))]
public partial record OrderItemDto;

[Facette(typeof(Order), NestedDtos = new[] { typeof(OrderItemDto) })]
public partial record OrderDto;

The generated code:

• FromSource: source.Items.Select(x => OrderItemDto.FromSource(x)).ToList()
• ToSource: Items.Select(x => x.ToSource()).ToList()
• Projection: Items = source.Items.Select(x => new OrderItemDto { ... }).ToList()

Primitive collections

Collections of primitive types (e.g., List<string>, int[]) are copied directly without element-level mapping:

public class Tag
{
    public List<string> Labels { get; set; } = new();
}

[Facette(typeof(Tag))]
public partial record TagDto;
// TagDto.Labels is List<string>, copied as-is

Custom collection converters

For collection types that Facette doesn't handle natively, you can use value conversions with Convert/ConvertBack on [MapFrom] to provide custom conversion logic.