Why you should ProjectTo when using the Automapper

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Automapper is a popular object-to-object mapping library for .NET. It allows you to create a map between two objects, so that you can convert an object of one type into an object of another type. This can be particularly useful when working with data transfer objects (DTOs) and entities in a layered architecture, where the DTOs are used to transfer data between the presentation and business layers.

One of the key features of Automapper is the ProjectTo method. This method is used to map an object to a new object, using a map that has been created with the CreateMap method.

So why should you use the ProjectTo method? Here are a few reasons:

  1. Better support for LINQ queries: The ProjectTo method is designed to work seamlessly with LINQ queries, allowing you to easily apply filtering and sorting to your mapping operations.
  2. Better support for lazy loading: If you are using a ORM (such as Entity Framework) that supports lazy loading, the ProjectTo method will automatically generate the necessary SQL to eagerly load any related entities that are included in the map. This can help to avoid the N+1 query problem.
  3. Strongly typed mapping: When you use the ProjectTo method, the resulting object is strongly typed, which can make your code more readable and easier to maintain.

In summary, the ProjectTo method is a powerful and efficient way to map objects in .NET using Automapper. It provides improved performance, better support for LINQ queries and lazy loading, and strongly typed mapping. If you are using Automapper in your .NET projects, it is definitely worth considering using the ProjectTo method to take advantage of these benefits.

Here is an example. Lets say we have the following models

public class Order
{
    public int Id { get; set; }
    public string CustomerName { get; set; }
    public string ItemName { get; set; }
    public int Quantity { get; set; }
    public decimal TotalPrice { get; set; }
}

public class OrderDTO
{
    public int OrderId { get; set; }
    public string CustomerName { get; set; }
    public string ItemName { get; set; }
    public int Quantity { get; set; }
    public decimal TotalPrice { get; set; }
}

We can use Automapper to map the Order model to the OrderDTO model like so:

var config = new MapperConfiguration(cfg => cfg.CreateMap<Order, OrderDTO>());
var mapper = config.CreateMapper();

var orders = new List<Order>
{
    new Order { Id = 1, CustomerName = "John", ItemName = "Item 1", Quantity = 2, TotalPrice = 10 },
    new Order { Id = 2, CustomerName = "Jane", ItemName = "Item 2", Quantity = 3, TotalPrice = 20 }
};

var orderDTOs = mapper.Map<IEnumerable<OrderDTO>>(orders);

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