Data Transfer Object (DTO)

The Data Transfer Object(DTO) is a container that transfers the API data between layers. Using this container, we can manipulate the data or change the structure of the data. Let's see how

Creating a Project

Relational DB - Getting Data including Data from Other Entities (Generic Repository Pattern)

Using DTO

To better organize, create a folder to hold the DTO class

Add a DTO class in the folder

Add properties to manipulate

Original Properties of an Entity

Updated Properties of the Entity

Go to the controller class. In the methods that fetche data, change the return type to DTO class we just created and map the original data to the DTO format then return

▶ For Individual Item

▶ For a List of Items

Run

Move to the API folder

cd /API

And run the app

dotnet watch

Befor DTO

After DTO

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※ Using an Extension

Nuget Gallery provides an extension that does the same work easily. Search the extension below in the Nuget Gallery and install it to webapi project

AutoMapper.Extensions.Microsoft.DependencyInject

Add a class to add the mapping codes

Add a constructor with a method shown below

public Mapper()
{
    CreateMap<Item, ItemDTO>();
}

Note that the extension uses the name and type of a property to automatically map the data. So if one of them is different you won't see the desired result. We can get around this with an additional settings

Append options that specifies what we want to use for a certain property to the mapping method

public Mapper()
{
    CreateMap<Item, ItemDTO>()
    .ForMember(d => d.ItemTarget, o => o.MapFrom(s => s.ItemTarget.Name))
    .ForMember(d => d.ItemType, o => o.MapFrom(s => s.ItemType.Name));
}

Adding Service

Go to Program.cs file and add the code below to register the extension as a service

builder.Services.AddAutoMapper(AppDomain.CurrentDomain.GetAssemblies());

Updating the Controller Class

Go to the controller class and inject the 'IMapper' interface

Use the injected mapper and update each method as shown below

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Manipulating Image Path

To automatically change the URL between the development and production environment. Go to 'appsettings.Development.json' and add the hostname

Inject the 'IConfiguration' interface to the controller

append the path we set up  in the 'appsettings.Development.json' in front of the image URL

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※ Manipulating Image Path with the Mapper Extension

To automatically change the URL between the development and production environment. Go to 'appsettings.Development.json' and add the hostname

Add a class to edit the image path

Inherit from 'IValueResolver' interface. The first value in the generic parameter is the original entity. The second and the third are the entity that we want to convert to and the type of the entity

Implement the interface and add a constructor

Add the code below in the implemented method.

'["URL"]' represents the URL we added in the 'appsettings.Development.json'

if (!string.IsNullOrEmpty(source.ImageURL))
{
    return _config["URL"] + source.ImageURL;
}
return null;

Go to the mapper class, add the URL mapper option as below

.ForMember(d => d.ItemType, o => o.MapFrom<URLMapper>());

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In this writing, we got to know what is DTO and how to use it.