Reusing common mapping code across common DTO classes

Question

I have 2 DTO classes that have multiple common properties, I'm trying to avoid having to repeat myself when writing mapping code for entity to DTO conversion, I'm wondering how I could achieve this, I have a feeling I need to probably use a Func or Action delegate to achieve this. For example I have 2 classes StudentDTO and EmployeeDTO:

public class StudentDTO : PersonDTO
{
    public int CourseId { get; set; }
    //other properties
}

public class EmployeeDTO : PersonDTO
{
    public int OccupationId { get; set; }
    //other properties
}

and both naturally inherit from PersonDTO:

public class PersonDTO
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string FamilyName { get; set; }
    public int Age { get; set; }
}

How could I reuse the mapping code that maps the common properties? Thanks.

Answer 1

You probably can do something like this (very basic and not elegant): (note Entity can off course be a DataReader, DataSet etc.)

public class Entity
{
    public string FirstName { get; set; }
    public string FamilyName { get; set; }
    public int CourseId { get; set; }
    public int OccupationId { get; set; }
}

public class BaseDto
{

}

public class PersonDto : BaseDto
{
    public string FirstName { get; set; }
    public string FamilyName { get; set; }

    public static void Map(Entity entity, PersonDto personDto)
    {
        personDto.FirstName = entity.FirstName;
        personDto.FamilyName = entity.FamilyName;
    }

}

public class StudentDto : PersonDto
{
    public int CourseId { get; set; }

    public static StudentDto Map(Entity entity)
    {
        var studentDto = new StudentDto { CourseId = entity.CourseId };
        // ..can call map to PersonDto if you want
        return studentDto;
    }
}

public class EmployeeDto : PersonDto
{
    public int OccupationId { get; set; }

    public static EmployeeDto Map(Entity entity)
    {
        var employeeDto = new EmployeeDto() { OccupationId = entity.OccupationId };
        // ..can call map to PersonDto if you want
        return employeeDto;
    }
}


public class Mapper<TDto>
    where TDto : BaseDto
{
    private TDto _dto;
    private readonly Entity _entity;

    public Mapper(Entity entity)
    {
        _entity = entity;
    }

    public Mapper<TDto> Map(Func<Entity, TDto> map)
    {
        _dto = map(_entity);
        return this;
    }

    public Mapper<TDto> Map<TBaseDto>(Action<Entity, TBaseDto> map)
        where TBaseDto : BaseDto
    {
        map(_entity, _dto as TBaseDto);
        return this;
    }

    public TDto Result
    {
        get { return _dto; }
    }
}

class Program
{
    static void Main(string[] args)
    {
        var studentEntity = new Entity() { FirstName = "John", FamilyName = "Doe", CourseId = 1 };

        var studentDto = new Mapper<StudentDto>(studentEntity)
            .Map(StudentDto.Map)
            .Map<PersonDto>(PersonDto.Map)
            .Result;
    }
}

Answer 2

Use a library.. that's what they are there for!

• Automapper
• ValueInjecter

In Automapper, your above mapping becomes incredibly simple:

Mapper.CreateMap<EmployeeDTO, StudentDTO>();
Mapper.CreateMap<StudentDTO, EmployeeDTO>();

..then when you want to map:

var studentInstance = ...; // go get student instance
var employee = Mapper.Map<Employee>(studentInstance);