Just started learning Mapster. From this article I learned that the generation of extension methods for existing entities is triggered using the GenerateMapper method, which is located in a custom configuration class that derives from IRegister.

In short:

1. Add the “dotnet mapster extension” command to the *.csproj file, for example:

<ItemGroup>
    <PackageReference Include="Mapster" Version="7.4.2-pre02"/>
</ItemGroup>

<Target Name="Mapster" AfterTargets="AfterBuild">
    <Exec WorkingDirectory="$(ProjectDir)" Command="dotnet tool restore" />
    <Exec WorkingDirectory="$(ProjectDir)" Command="dotnet mapster extension -a &quot;$(TargetDir)$(ProjectName).dll&quot;" />
    <Exec WorkingDirectory="$(ProjectDir)" Command="dotnet mapster mapper -a &quot;$(TargetDir)$(ProjectName).dll&quot;" />
</Target>

2. Create a configuration class that derives from IRegister:

public class MapperConfig : IRegister {
    private const MapType MapAll = MapType.Map | MapType.MapToTarget | MapType.Projection;

    public void Register(TypeAdapterConfig config) {

        config.NewConfig<Poco, Dto>()
            .TwoWays()
            .GenerateMapper(MapAll);
    }
}

3. Run Build.