Struggling with mapping readonly ICollection property

[akordowski]

Discussed in #688

^{Originally posted by akordowski March 24, 2024}
Hi everyone!

I am currently struggling with the mapping of a readonly ICollection property. I followed the instructions but I can't make it work. The readonly collection is not populated with the mapped content. What am I making wrong? Have anyone an idea how I can make it work?

Here the code:

Programm.cs

var config = TypeAdapterConfig.GlobalSettings;
config.Scan(typeof(ChannelMapping).Assembly);
config.Default.UseDestinationValue(m => m.SetterModifier == AccessModifier.None &&
                                        m.Type.IsGenericType &&
                                        m.Type.GetGenericTypeDefinition() == typeof(ICollection<>));

var channelSrc = new MapsterTest.Objects.Source.Channel
{
    ChannelId = "123",
    Thumbnails = new MapsterTest.Objects.Source.ThumbnailDetails
    {
        Default = new MapsterTest.Objects.Source.Thumbnail
        {
            Url = "https://www.youtube.com/default.jpg"
        },
        Medium = new MapsterTest.Objects.Source.Thumbnail
        {
            Url = "https://www.youtube.com/medium.jpg"
        },
        High = new MapsterTest.Objects.Source.Thumbnail
        {
            Url = "https://www.youtube.com/high.jpg"
        }
    }
};

// Thumbnails are mapped correctly to a collection
var thumbnailsDest = channelSrc.Thumbnails.Adapt<ICollection<MapsterTest.Objects.Destination.Thumbnail>>().ToList();

// channelDest.Thumbnails collection is empty
var channelDest = channelSrc.Adapt<MapsterTest.Objects.Destination.Channel>();

ThumbnailMapping.cs

public class ThumbnailMapping : IRegister
{
    public void Register(TypeAdapterConfig config)
    {
        config.ForType<Objects.Source.ThumbnailDetails, ICollection<Objects.Destination.Thumbnail>>()
            .MapWith(src => MapThumbnailDetails(src).ToList());
    }

    private static IEnumerable<Objects.Destination.Thumbnail> MapThumbnailDetails(Objects.Source.ThumbnailDetails thumbnailDetails)
    {
        yield return MapThumbnail(thumbnailDetails.Default, "Default");
        yield return MapThumbnail(thumbnailDetails.Medium, "Medium");
        yield return MapThumbnail(thumbnailDetails.High, "High");
    }

    private static Objects.Destination.Thumbnail MapThumbnail(
        Objects.Source.Thumbnail thumbnail,
        string thumbnailType) =>
        new()
        {
            Type = thumbnailType,
            Url = thumbnail.Url.Trim(),
        };
}

Channel.cs (Destination)

public class Channel
{
    public string ChannelId { get; set; } = default!;
    public ICollection<Thumbnail> Thumbnails { get; } = new List<Thumbnail>();
}

Thumbnail.cs (Destination)

public class Thumbnail
{
    public string Type { get; set; } = default!;
    public string Url { get; set; } = default!;
}

Channel.cs (Source)

public class Channel
{
    public string ChannelId { get; set; } = default!;
    public ThumbnailDetails Thumbnails { get; set; } = default!;
}

ThumbnailDetails.cs (Source)

public class ThumbnailDetails
{
    public Thumbnail? Default { get; set; }
    public Thumbnail? Medium { get; set; }
    public Thumbnail? High { get; set; }
}

Thumbnail.cs (Source)

public class Thumbnail
{
    public string Url { get; set; } = default!;
}

[steingran]

@akordowski I have the same issue. Did you ever find a solution?

This project is starting to look abandoned — no commits since September 2023, and no release since then. And issues opened are not answered... Is it time to move on to a different mapper?

[akordowski]

This is how I solved the problem. It's far from being an optimal solution but it works. It was a special case, but it might give you an idea. Hope it helps you.

public class SrcClassMapping : IRegister
{
    public void Register(TypeAdapterConfig config)
    {
        config
            .ForType<DestClass, ICollection<SrcClass>>()
            .MapWith(src => MapCollection(src, null))
            .MapToTargetWith((src, dest) => MapCollection(src, dest));
    }

    private static ICollection<SrcClass> MapCollection(
        DestClass? destObj,
        ICollection<SrcClass>? srcCollection)
    {
        srcCollection ??= new List<SrcClass>();

        if (destObj is null)
            return srcCollection;

        // Custom mapping

        return srcCollection;
    }
}

[steingran]

@akordowski Great, thanks! Will give it a try

[stagep]

In order to identify issues that are still active, we are closing issues that we believe are either resolved or are dormant. If your issue is still active then please reopen. Thanks.

[akordowski]

@stagep Please reopen, as I can only comment. Thank you.

[DocSvartz]

Hello @akordowski. Destination Class does it really look like you indicated?

public class Channel
{
    public string ChannelId { get; set; } = default!;
    public ICollection<Thumbnail> Thumbnails { get; } = new List<Thumbnail>();
}

it doesn't have any additional constructors?

[akordowski]

Yes, the destination class looks exactly like this and don't have any constructors.

[DocSvartz]

Ok, I'm starting to research this problem.
I'll try to come back soon with an explanation or a solution :)