Mapping with Mapperly

The rule

Mapping code is generated at compile time by Mapperly (Riok.Mapperly), never written by hand and never done by reflection. Infrastructure's MovieReviewsMapper (src/Infrastructure/Databases/MovieReviews/Mapping/MovieReviewsMapper.cs) maps database models to Application entities. It only maps that way, because writes build the database model directly (data-access-ef-core). Add a mapping in the other direction only when something calls it. Presentation layers that need their own response models have their own mapper beside them.

Mapperly reports unmapped members as RMG warnings, and warnings fail the build, so every member is either mapped or explicitly ignored.

Steps

1. Add the property to both sides with the same name. Mapperly maps it with no other change.
2. A property that only exists on one side gets [MapperIgnoreSource(nameof(...))] (it's on the source only) or [MapperIgnoreTarget(nameof(...))] (on the target only) on each affected method.
3. Different names on purpose? Use [MapProperty(nameof(Source.A), nameof(Target.B))].
4. Use the aliases at the top of the mapper (AppMovie, InfraMovie) so it's always clear which side is which.
5. Build. Fix every RMG warning rather than suppressing it.

Example

// src/Infrastructure/Databases/MovieReviews/Mapping/MovieReviewsMapper.cs
[Mapper]
internal partial class MovieReviewsMapper
{
    [MapperIgnoreSource(nameof(InfraMovie.DateCreated))]
    [MapperIgnoreSource(nameof(InfraMovie.DateModified))]
    public partial AppMovie ToDomain(InfraMovie movie);
}

Don't

• Use AutoMapper. It's commercially licensed now, and it maps by reflection at runtime.
• Write a mapping by hand when Mapperly can generate it.
• Add <NoWarn> for RMG codes.
• Map in a handler. Repositories return entities already mapped.

Check

dotnet build