我在 ASP.NET Core
应用程序中使用库 MediatR
。
我有以下实体 Ad
:
public class Ad
{
public Guid AdId { get; set; }
public AdType AdType { get; set; }
public double Cost { get; set; }
public string Content { get; set; }
// ...
}
public enum AdType
{
TextAd,HtmlAd,BannerAd,VideoAd
}
我想介绍制作新广告的功能。为此,我创建了以下命令:
public class CreateAdCommand : IRequest<Guid>
{
public AdType AdType { get; set; }
public double Cost { get; set; }
public string Content { get; set; }
public class Handler : IRequestHandler<CreateAdCommand,Guid>
{
private readonly MyDbContext _context;
public Handler(MyDbContext context)
{
_context = context;
}
public async Task<Guid> Handle(CreateAdCommand request,CancellationToken cancellationToken)
{
var ad = new Ad {AdType = request.AdType,Cost = request.Cost,Content = request.Content};
_context.Ads.Add(ad);
_context.SaveChangesAsync();
return ad.AdId;
}
}
}
这段代码效果很好。但这里有一个大问题:每种广告类型都有一些额外的广告创建过程逻辑(例如,在创建 TextAd
类型的广告时,我们需要在广告内容中查找关键字)。最简单的解决方案是:
public async Task<Guid> Handle(CreateAdCommand request,CancellationToken cancellationToken)
{
var ad = new Ad {AdType = request.AdType,Content = request.Content};
_context.Ads.Add(ad);
_context.SaveChangesAsync();
switch (request.AdType)
{
case AdType.TextAd:
// Some additional logic here...
break;
case AdType.HtmlAd:
// Some additional logic here...
break;
case AdType.BannerAd:
// Some additional logic here...
break;
case AdType.VideoAd:
// Some additional logic here...
break;
}
return ad.AdId;
}
这个解决方案违反了开放封闭原则(当我创建一个新的广告类型时,我需要在 case
内创建一个新的 CreateAdCommand
)。
我还有一个想法。我可以为每种广告类型创建单独的命令(例如,CreateTextAdCommand
、CreateHtmlAdCommand
、CreateBannerAdCommand
、CreateVideoAdCommand
)。此解决方案遵循开放封闭原则(当我创建新的广告类型时,我需要为该广告类型创建一个新命令 - 我不需要更改现有代码)。
public class CreateTextAdCommand : IRequest<Guid>
{
public double Cost { get; set; }
public string Content { get; set; }
public class Handler : IRequestHandler<CreateTextAdCommand,Guid>
{
private readonly MyDbContext _context;
public Handler(MyDbContext context)
{
_context = context;
}
public async Task<Guid> Handle(CreateTextAdCommand request,CancellationToken cancellationToken)
{
var ad = new Ad {AdType = AdType.TextAd,Content = request.Content};
_context.Ads.Add(ad);
await _context.SaveChangesAsync();
// Some additional logic here ...
return ad.AdId;
}
}
}
public class CreateHtmlAdCommand : IRequest<Guid>
{
public double Cost { get; set; }
public string Content { get; set; }
public class Handler : IRequestHandler<CreateHtmlAdCommand,Guid>
{
private readonly MyDbContext _context;
public Handler(MyDbContext context)
{
_context = context;
}
public async Task<Guid> Handle(CreateHtmlAdCommand request,CancellationToken cancellationToken)
{
var ad = new Ad {AdType = AdType.HtmlAd,Content = request.Content};
_context.Ads.Add(ad);
await _context.SaveChangesAsync();
// Some additional logic here ...
return ad.AdId;
}
}
}
// The same for CreateBannerAdCommand and CreateVideoAdCommand.
此解决方案遵循开放封闭原则,但违反了 DRY 原则。我该如何解决这个问题?