.NET

Conditionally Applying Decorators in .NET Dependency Injection?

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In .NET DI, you can conditionally apply the Decorator Pattern based on configuration or runtime conditions using IServiceCollection.

public class LoggingExpenseServiceDecorator : IExpenseService { private readonly IExpenseService _inner; private readonly ILogger<LoggingExpenseServiceDecorator> _logger;

`public LoggingExpenseServiceDecorator(IExpenseService inner, ILogger<LoggingExpenseServiceDecorator> logger)`
`{`
    `_inner = inner;`
    `_logger = logger;`
`}`

`public async Task<string> ProcessExpenseAsync(decimal amount)`
`{`
    `_logger.LogInformation($"Processing expense: {amount} USD");`

    `var result = await _inner.ProcessExpenseAsync(amount);`

    `_logger.LogInformation($"Expense processed successfully: {result}");`

    `return result;`
`}`

}

In Program.cs

var builder = WebApplication.CreateBuilder(args);
var services = builder.Services;

// Register the base service
services.AddScoped<IExpenseService, ExpenseService>();

// Conditionally apply the decorator
bool useLoggingDecorator = builder.Configuration.GetValue<bool>("UseLoggingDecorator");

if (useLoggingDecorator)
{
    services.AddScoped<IExpenseService>(provider =>
    {
        var innerService = provider.GetRequiredService<ExpenseService>();
        var logger = provider.GetRequiredService<ILogger<LoggingExpenseServiceDecorator>>();
        return new LoggingExpenseServiceDecorator(innerService, logger);
    });
}

var app = builder.Build();

How to register multiple implementations for the same interface and resolve it?

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Use of Decorator Pattern

• https://timdeschryver.dev/blog/the-decorator-pattern-using-nets-dependency-injection
• https://medium.com/@anderson.buenogod/mastering-the-decorator-pattern-in-c-net-8-advanced-use-cases-and-best-practices-378974abe9be

Approach 1

Approach 2

Approach 3 - Using Keyed Services to Register Multiple Implementations of the Same Interface

References

• https://code-maze.com/aspnetcore-register-multiple-interface-implementations/