Refactoring to Use the Parameter Object Pattern in .NET

When developing software in .NET, it’s common to encounter methods with numerous parameters. This can make the code harder to read, maintain, and extend. A powerful refactoring technique to address this issue is the Parameter Object pattern, which encapsulates method parameters into a single Data Transfer Object (DTO). This blog post will delve into the details of this pattern, its benefits, and how to implement it in your .NET applications.

Why Refactor?

Identical groups of parameters are often encountered in multiple methods. This causes code duplication of both the parameters themselves and of related operations. By consolidating parameters in a single class, you can also move the methods for handling this data there as well, freeing the other methods from this code.

Benefits

1. More Readable Code: Instead of a hodgepodge of parameters, you see a single object with a comprehensible name.

2. Reduced Code Duplication: Identical groups of parameters scattered throughout your codebase create their own kind of duplication, which the Parameter Object pattern helps eliminate.

Example Implementation

Consider the following service interface, which has several methods with multiple parameters:

public interface IOrderProcessingService
{
    Task ProcessOrder(int orderId, string customerName, string address, DateTime orderDate, decimal orderAmount, string paymentMethod);
    Task<IEnumerable<OrderSummary>> GetOrderSummaries(int customerId, DateTime orderDate, string region, int? storeId = null);
    Task<decimal> CalculateTotalSales(int productId, string region, string category, bool includeDiscounts, int? storeId = null);
}

Using the Parameter Object pattern, we can refactor this to make it more maintainable.

1. Create DTO Classes:

public class OrderProcessingParams
{
    public int OrderId { get; }
    public string CustomerName { get; }
    public string Address { get; }
    public DateTime OrderDate { get; }
    public decimal OrderAmount { get; }
    public string PaymentMethod { get; }

    public OrderProcessingParams(int orderId, string customerName, string address, DateTime orderDate, decimal orderAmount, string paymentMethod)
    {
        OrderId = orderId;
        CustomerName = customerName;
        Address = address;
        OrderDate = orderDate;
        OrderAmount = orderAmount;
        PaymentMethod = paymentMethod;
    }
}

public class OrderSummaryParams
{
    public int CustomerId { get; }
    public DateTime OrderDate { get; }
    public string Region { get; }
    public int? StoreId { get; }

    public OrderSummaryParams(int customerId, DateTime orderDate, string region, int? storeId)
    {
        CustomerId = customerId;
        OrderDate = orderDate;
        Region = region;
        StoreId = storeId;
    }
}

public class SalesCalculationParams
{
    public int ProductId { get; }
    public string Region { get; }
    public string Category { get; }
    public bool IncludeDiscounts { get; }
    public int? StoreId { get; }

    public SalesCalculationParams(int productId, string region, string category, bool includeDiscounts, int? storeId)
    {
        ProductId = productId;
        Region = region;
        Category = category;
        IncludeDiscounts = includeDiscounts;
        StoreId = storeId;
    }
}

2. Refactor the Service Interface:

public interface IOrderProcessingService
{
    Task ProcessOrder(OrderProcessingParams parameters);
    Task<IEnumerable<OrderSummary>> GetOrderSummaries(OrderSummaryParams parameters);
    Task<decimal> CalculateTotalSales(SalesCalculationParams parameters);
}

3. Update Method Implementations:

public class OrderProcessingService : IOrderProcessingService
{
    public async Task ProcessOrder(OrderProcessingParams parameters)
    {
        // Use parameters.OrderId, parameters.CustomerName, etc.
    }

    public async Task<IEnumerable<OrderSummary>> GetOrderSummaries(OrderSummaryParams parameters)
    {
        // Use parameters.CustomerId, parameters.OrderDate, etc.
    }

    public async Task<decimal> CalculateTotalSales(SalesCalculationParams parameters)
    {
        // Use parameters.ProductId, parameters.Region, etc.
    }
}

Conclusion

By applying the Parameter Object pattern, we can significantly improve the readability and maintainability of our code. This pattern helps us to encapsulate related parameters into cohesive objects, reducing code duplication and making our methods easier to work with. In your .NET projects, consider refactoring methods with numerous parameters into parameter objects to reap these benefits.