缓存装饰器

此示例演示如何使用 Decorator 模式向 DbProductRepository 添加缓存功能。这种方法遵循 SOLID 原则， 因为它允许你在不违反单一责任原则或开放/封闭原则的情况下添加缓存。

public interface IProductRepository
{
    Product GetProduct(int id);
}

public class DbProductRepository : IProductRepository
{
    public Product GetProduct(int id)
    {
        //return Product retrieved from DB
    }
}

public class ProductRepositoryCachingDecorator : IProductRepository
{
    private readonly IProductRepository _decoratedRepository;
    private readonly ICache _cache;
    private const int ExpirationInHours = 1;

    public ProductRepositoryCachingDecorator(IProductRepository decoratedRepository, ICache cache)
    {
        _decoratedRepository = decoratedRepository;
        _cache = cache;
    }

    public Product GetProduct(int id)
    {
        var cacheKey = GetKey(id);
        var product = _cache.Get<Product>(cacheKey);
        if (product == null)
        {
            product = _decoratedRepository.GetProduct(id);
            _cache.Set(cacheKey, product, DateTimeOffset.Now.AddHours(ExpirationInHours));
        }
        
        return product;
    }

    private string GetKey(int id) => "Product:" + id.ToString();
}

public interface ICache
{
    T Get<T>(string key);
    void Set(string key, object value, DateTimeOffset expirationTime)
}

用法：

var productRepository = new ProductRepositoryCachingDecorator(new DbProductRepository(), new Cache());
var product = productRepository.GetProduct(1);

调用 GetProduct 的结果将是：从缓存中检索产品（装饰器责任），如果产品不在缓存中，则继续调用 DbProductRepository 并从 DB 检索产品。此产品可以添加到缓存后，以便后续调用不会命中 DB。