How to Map Data Between Object and Interface in C#

When working with C#, it's common to encounter scenarios where you need to map data from one type to another, especially when dealing with interfaces and object hierarchies. In this article, we'll explore how to efficiently map a data structure represented by an object to an interface while maintaining the integrity of your application's architecture.

Understanding the Problem

The issue you're facing revolves around mapping from a MyViewModel class to a MyDbModel class, where the selections in both classes are represented differently. The MyViewModel class contains lists of ViewItem objects, while the MyDbModel class utilizes an interface, IPageSelection, which further contains a list of IMyDbItem items. This mismatch can lead to complications, especially when using mapping libraries like AutoMapper.

Class Definitions

Let's break down the classes involved in your mapping scenario:

ViewModel Class

public class MyViewModel
{
    public int ViewModelId { get; set; }
    public IList Page1Selections { get; set; }
    public IList Page2Selections { get; set; }
}

ViewItem Class

public class ViewItem
{
    public int ItemId { get; set; }
    public bool IsSelected { get; set; }
}

Database Model

public class MyDbModel
{
    public int DbModelId { get; set; }
    public IPageSelection Page1Selections { get; set; }
    public IPageSelection Page2Selections { get; set; }
}

Page Selection Interface and Implementation

public interface IPageSelection
{
    int PageNumber { get; set; }
    IList PageSelections { get; set; }
}

public class PageSelection : IPageSelection
{
    public int PageNumber { get; set; }
    public IList PageSelections { get; set; }
}

Item Interface

public interface IMyDbItem
{
    int ItemId { get; set; }
    bool IsSelected { get; set; }
}

public class MyDbItem : IMyDbItem
{
    public int ItemId { get; set; }
    public bool IsSelected { get; set; }
}

Setting Up AutoMapper

AutoMapper is a powerful library that helps simplify the mapping between objects. To set it up for your classes, follow these steps:

Mapper.Initialize(cfg =>
{
    cfg.BindingFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance;
    cfg.CreateMap()
        .ForMember(dest => dest.Page1Selections, opt => opt.MapFrom(src => new PageSelection
        {
            PageNumber = 1,
            PageSelections = src.Page1Selections.Select(v => new MyDbItem
            {
                ItemId = v.ItemId,
                IsSelected = v.IsSelected
            }).ToList()
        }))
        .ForMember(dest => dest.Page2Selections, opt => opt.MapFrom(src => new PageSelection
        {
            PageNumber = 2,
            PageSelections = src.Page2Selections.Select(v => new MyDbItem
            {
                ItemId = v.ItemId,
                IsSelected = v.IsSelected
            }).ToList()
        }));

    cfg.CreateMap()
        .ConvertUsing(src => new MyDbItem
        {
            ItemId = src.ItemId,
            IsSelected = src.IsSelected
        });
});

Mapping the Data

With your AutoMapper configuration set up, you can now map MyViewModel to MyDbModel efficiently.

MyViewModel myVm = new MyViewModel
{
    ViewModelId = 123,
    Page1Selections = new List
    {
        new ViewItem() { ItemId = 1, IsSelected = true }
    },
    Page2Selections = new List
    {
        new ViewItem() { ItemId = 2, IsSelected = true }
    }
};

MyDbModel myDb = Mapper.Map(myVm);

Make sure to run the mapping within a safe environment to avoid any exceptions and check the resulting myDb object to confirm the mapping was successful.

Conclusion

Mapping data between objects and interfaces in C# can be complex when dealing with hierarchical data structures. By leveraging AutoMapper and setting up clear mapping configurations, you can streamline the process while ensuring your application's architecture remains clean and maintainable. Remember to encapsulate the mapping logic within a manageable function, and always test your mappings to catch any potential issues early.

Frequently Asked Questions

What is AutoMapper?

AutoMapper is a popular library in .NET that facilitates the automatic mapping of objects by creating mappings between different types.

Can I map objects with mixed levels of hierarchy?

Yes, AutoMapper allows you to create complex mappings, including hierarchical structures, by defining mappings for nested properties.

What should I do if I encounter mapping exceptions?

Debug the AutoMapper configuration, ensure that properties in the source and destination types match, and review the mapping expressions to fix the issues.