Issues mapping some some collection properties and dates with IQueryable

[Atulin]

Source:

public class Story
{
	// ...
	public DateTime CreationDate { get; set; }
	public DateTime? PublicationDate { get; set; }
	public IList<Chapter> Chapters { get; set; }
}

public class Chapter
{
	// ...
	public CommentsThread CommentsThread { get; set; }
}

public class CommentsThread 
{
	// ...
	public int CommentsCount { get; set; }
}

Target:

public class StoryDetails
{
	public DateTime ReleaseDate { get; set; }
	public bool IsPublished { get; set; }
	public bool CommentsCount { get; set; }
}

Mapper:

[Mapper]
public static partial class StoryMapper
{
	public static partial IQueryable<StoryDetails> ProjectToDetails(this IQueryable<Story> q);

	// Does not work
	private static int MapCommentsCount(IList<Chapter> chapters)
		=> chapters.Sum(c => c.CommentsThread.CommentsCount);

	// Neither do those two
	private static DateTime MapReleaseDate(Story story) => story.PublicationDate ?? story.CreationDate;
	private static bool MapIsPublished(DateTime? publicationDate) => publicationDate != null;
}

[latonz]

Is the posted target class exactly as it is in your code? The error message indicates that the members are required, which is not the case in the posted code.
Anyway, Mapperly does not know it should map Story.Chapters to StoryDetails.CommentsCount. The same for the other properties. You can use MapProperty in combination with MapProperty.Use, see docs or before and after map (docs).

[Atulin]

The classes do have more properties in them, yes.

I tried using the Use but to no effect, it generated no new code. I'll give it another shot and report back.

[latonz]

Note: you need to apply the MapProperty to a mapping method with the classes as parameter / return types, not wrapped in IQueryable. Otherwise Mapperly tries to apply the MapProperty attribute to the IQueryable which doesn't have these properties.

public static partial IQueryable<StoryDetails> ProjectToDetails(this IQueryable<Story> q);

[MapProperty(...)]
private static partial StoryDetails Map(Story source);

Mapperly will pick up the configuration from the Map method whenever mapping from Story to StoryDetails.
See also the documentation.

[Atulin]

Ah, that was probably my mistake, then! I was adding [MapProperty] to the IQueryable mapping