Querying a database with Dapper

Question

In the current project that I am working on, we are using dapper to query the database and sometime when mapping from dynamic types to concrete types we end up with a messy block of code.

I created a folder called mappers and have created an Interface<T>, an abstract class inheriting from that interface and I have also set up my IOC to map according to naming conventions so that I can inject my mappers through the constructor of my query classes.

public interface IMapper<out T>
    {
        T Map(SqlMapper.GridReader reader);
    }

    public abstract class MapperBase<T> : IMapper<T>
    {
        public abstract T Map(SqlMapper.GridReader reader);
    }

    public class UserDto
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

    public class UserDtoMapper : MapperBase<UserDto>
    {
        public override UserDto Map(SqlMapper.GridReader reader)
        {
            return reader.Read().Select(x => new UserDto()
            {
                Id = x.Id,
                Name = x.Name
            }).SingleOrDefault();
        }
    }

    public class QueryObject
    {
        private IMapper<UserDto> userDtoMapper; 

        public QueryObject(IMapper<UserDto> userDtoMapper)
        {
            this.userDtoMapper = userDtoMapper;
        }

        public UserDto Query(int id)
        {
            ..........
             return userDtoMapper.Map(reader)
            ...
        }
    }

Answer 1

Setting aside that you won't go with a Mapping framework like Jeroen Vannevel suggested in his comment, this basically looks good but can still be improved.

I don't see any value added by creating an abstract class which implements the IMapper<T> interface. So you better just do it like

public class UserDtoMapper : IMapper<UserDto>
{
    public UserDto Map(SqlMapper.GridReader reader)
    {
        return reader.Read().Select(x => new UserDto()
        {
            Id = x.Id,
            Name = x.Name
        }).SingleOrDefault();
    }
}

But if you travel this route you should do it right and also make QueryObject class generic like

public class QueryObject<T>
{
    private IMapper<T> mapper; 

    public QueryObject(IMapper<T> mapper)
    {
        this.mapper = mapper;
    }

    public T Query(int id)
    {
        ..........
         return mapper.Map(reader)
        ...
    }
}