使用策略者模式减少switch case 语句

策略者模式

很简单的一个定义：抽象策略（Strategy）类：定义了一个公共接口，各种不同的算法以不同的方式实现这个接口，环境角色使用这个接口调用不同的算法，一般使用接口或抽象类实现。

场景

在这之前，你需要看这个文章SPA+.NET Core3.1 GitHub第三方授权登录,了解如何实现第三方授权登录。

我们这里使用策略者模式应用实践，实现第三方授权登录，支持QQ，Gitee,GitHub登录，并且如何把switch case的逻辑判断去掉。

我们先按正常的思路写代码，引用如下类库

• AspNet.Security.OAuth.Gitee
• AspNet.Security.OAuth.GitHub
• AspNet.Security.OAuth.QQ

我们会创建一个Service，这个Service包含了保存Github，QQ，Gitee信息的接口。由于三者之间，数据都是以Claims的情况存到ClaimsPrincipal中，键各不相同，只能独立处理

public  interface IUserIdentityService
 {
    Task<long> SaveGitHubAsync(ClaimsPrincipal principal, string openId);
    Task<long> SaveQQAsync(ClaimsPrincipal principal, string openId);
    Task<long> SaveGiteeAsync(ClaimsPrincipal principal, string openId);
 }

实现,保存登录后的授权信息，生成账号，并返回生成的用户id，伪代码如下

  public class UserIdentityService :ApplicationService, IUserIdentityService
  {

        public async Task<long> SaveGitHubAsync(ClaimsPrincipal principal, string openId)
        {
            return userId;
        }	

         public async Task<long> SaveQQAsync(ClaimsPrincipal principal, string openId)
         {
             return userId;
         }
        public async Task<long> SaveGiteeAsync(ClaimsPrincipal principal, string openId)
         {
              return userId;
         }
  }

这时候我们怎么调用 呢，provider为GitHub,QQ,Gitee这种字符串，登录成功后，会回调到此地址，这时，根据provider选择不同的方法进行保存用户数据

Oauth2Controller

[HttpGet("signin-callback")]
public async Task<IActionResult> Home(string provider, string redirectUrl = "")
{
    AuthenticateResult authenticateResult = await _contextAccessor.HttpContext.AuthenticateAsync(provider);
    if (!authenticateResult.Succeeded) return Redirect(redirectUrl);

    var openIdClaim = authenticateResult.Principal.FindFirst(ClaimTypes.NameIdentifier);
    if (openIdClaim == null || string.IsNullOrWhiteSpace(openIdClaim.Value))
        return Redirect(redirectUrl);

    long id = 0;
    switch (provider)
    {
        case LinUserIdentity.GitHub:
            id = await _userCommunityService.SaveGitHubAsync(authenticateResult.Principal, openIdClaim.Value);
            break;

        case LinUserIdentity.QQ:
            id = await _userCommunityService.SaveQQAsync(authenticateResult.Principal, openIdClaim.Value);
            break;

        case LinUserIdentity.Gitee:
            id = await _userCommunityService.SaveGiteeAsync(authenticateResult.Principal, openIdClaim.Value);
            break;
        default:
            _logger.LogError($"未知的privoder:{provider},redirectUrl:{redirectUrl}");
            throw new LinCmsException($"未知的privoder:{provider}！");
    }

    //xxx更多参考 https://github.com/luoyunchong/lin-cms-dotnetcore/issues/9
    string token ="";

    return Redirect($"{redirectUrl}#login-result?token={token}");
}

一看上面的代码，也没毛病，原本也没想要再优化，但后来，我想实现账号绑定。比如，我先用QQ登录，退出后，再用gitee登录，这时就是二个账号了。我们可以在QQ登录的情况下，点击绑定账号，实现二者之间的绑定。如下表结构也是支持此功能的。只要他们的create_userid是一个，就是同一个账号。

按上面的思路，绑定也是lin_user_identity表的数据操作，我们还放到IUserIdentityService服务中。这时就带来新的问题，这个接口在膨胀，他的实现类就更膨胀了。

public  interface IUserIdentityService
 {
    Task<long> SaveGitHubAsync(ClaimsPrincipal principal, string openId);
    Task<long> SaveQQAsync(ClaimsPrincipal principal, string openId);
    Task<long> SaveGiteeAsync(ClaimsPrincipal principal, string openId);

     Task<UnifyResponseDto>  BindGitHubAsync(ClaimsPrincipal principal, string openId, long userId);
     Task<UnifyResponseDto>  BindQQAsync(ClaimsPrincipal principal, string openId, long userId);
     Task<UnifyResponseDto>  BindGiteeAsync(ClaimsPrincipal principal, string openId, long userId);
 }

实现类多了一些方法，也能通过私有方法减少一些重复方法，但总感觉这样的设计实在是太挫了。

这样代码中包含了不同的处理逻辑，一看就是违反了职责单一原则。

   public async Task<UnifyResponseDto> BindGitHubAsync(ClaimsPrincipal principal, string openId, long userId)
        {
            string name = principal.FindFirst(ClaimTypes.Name)?.Value;
            return await this.BindAsync(LinUserIdentity.GitHub, name, openId, userId);
        }

        public async Task<UnifyResponseDto> BindQQAsync(ClaimsPrincipal principal, string openId, long userId)
        {
            string nickname = principal.FindFirst(ClaimTypes.Name)?.Value;
            return await this.BindAsync(LinUserIdentity.QQ, nickname, openId, userId);
        }

        public async Task<UnifyResponseDto> BindGiteeAsync(ClaimsPrincipal principal, string openId, long userId)
        {
            string name = principal.FindFirst(ClaimTypes.Name)?.Value;
            return await this.BindAsync(LinUserIdentity.Gitee, name, openId, userId);
        }

        private async Task<UnifyResponseDto> BindAsync(string identityType, string name, string openId, long userId)
        {
            LinUserIdentity linUserIdentity = await _userIdentityRepository.Where(r => r.IdentityType == identityType && r.Credential == openId).FirstAsync();
            if (linUserIdentity == null)
            {
                var userIdentity = new LinUserIdentity(identityType, name, openId, DateTime.Now);
                userIdentity.CreateUserId = userId;
                await _userIdentityRepository.InsertAsync(userIdentity);
                return UnifyResponseDto.Success("绑定成功");
            }
            else
            {
                return UnifyResponseDto.Error("绑定失败,该用户已绑定其他账号");
            }
        }

第三方账号绑定回调，调用方法如下，非全部代码，

[HttpGet("signin-bind-callback")]
public async Task<IActionResult> SignInBindCallBack(string provider, string redirectUrl = "", string token = "")
{
    //更多xxx代码
    long userId = 11;
    UnifyResponseDto unifyResponseDto;
    switch (provider)
    {
        case LinUserIdentity.GitHub:
            unifyResponseDto = await _userCommunityService.BindGitHubAsync(authenticateResult.Principal, openIdClaim.Value, userId);
            break;
        case LinUserIdentity.QQ:
            unifyResponseDto = await _userCommunityService.BindQQAsync(authenticateResult.Principal, openIdClaim.Value, userId);
            break;
        case LinUserIdentity.Gitee:
            unifyResponseDto = await _userCommunityService.BindGiteeAsync(authenticateResult.Principal, openIdClaim.Value, userId);
            break;
        default:
            _logger.LogError($"未知的privoder:{provider},redirectUrl:{redirectUrl}");
            unifyResponseDto = UnifyResponseDto.Error($"未知的privoder:{provider}！");
            break;
    }

    return Redirect($"{redirectUrl}#bind-result?code={unifyResponseDto.Code.ToString()}&message={HttpUtility.UrlEncode(unifyResponseDto.Message.ToString())}");
}

那么，我们如何优化呢。我们也看下表结构。

表结构

1. 用户表 lin_user

字段	备注	类型
id	主键Id	bigint
username	用户名	varchar

2. 用户身份认证登录表 lin_user_identity

字段	备注	类型
id	char	主键Id
identity_type	varchar	认证类型Password，GitHub、QQ、WeiXin等
identifier	varchar	认证者，例如 用户名,手机号，邮件等，
credential	varchar	凭证，例如 密码,存OpenId、Id，同一IdentityType的OpenId的值是唯一的
create_user_id	bigint	绑定的用户Id
create_time	datetime

实体类

• 用户信息 LinUser

    [Table(Name = "lin_user")]
    public class LinUser : FullAduitEntity
    {
        public LinUser() { }

        /// <summary>
        /// 用户名
        /// </summary>
        [Column(StringLength = 24)]
        public string Username { get; set; }

        [Navigate("CreateUserId")]
        public virtual ICollection<LinUserIdentity> LinUserIdentitys { get; set; }

    }

• 用户身份认证登录表 LinUserIdentity

    [Table(Name = "lin_user_identity")]
    public class LinUserIdentity : FullAduitEntity<Guid>
    {
        public const string GitHub = "GitHub";
        public const string Password = "Password";
        public const string QQ = "QQ";
        public const string Gitee = "Gitee";
        public const string WeiXin = "WeiXin";

        /// <summary>
        ///认证类型， Password，GitHub、QQ、WeiXin等
        /// </summary>
        [Column(StringLength = 20)]
        public string IdentityType { get; set; }

        /// <summary>
        /// 认证者，例如 用户名,手机号，邮件等，
        /// </summary>
        [Column(StringLength = 24)]
        public string Identifier { get; set; }

        /// <summary>
        ///  凭证，例如 密码,存OpenId、Id，同一IdentityType的OpenId的值是唯一的
        /// </summary>
        [Column(StringLength = 50)]
        public string Credential { get; set; }

    }

如何将六个方法，拆到不同的类中呢。

1. 创建一个IOAuth2Service的接口，里面有二个方法，一个将授权登录后的信息保存，另一个是绑定和当前用户绑定。

   public interface IOAuth2Service
    {
        Task<long> SaveUserAsync(ClaimsPrincipal principal, string openId);

        Task<UnifyResponseDto> BindAsync(ClaimsPrincipal principal, string identityType, string openId, long userId);
    }

然后，分别创建，GiteeOAuth2Service，GithubOAuth2Serivice，QQOAuth2Service

在这之前，因为整体逻辑相似，我们可以提取一个抽象类，在抽象类中写通用 的逻辑，子类只需要 实现SaveUserAsync，具体不同的逻辑了。

   public abstract class OAuthService : IOAuth2Service
    {
        private readonly IAuditBaseRepository<LinUserIdentity> _userIdentityRepository;

        public OAuthService(IAuditBaseRepository<LinUserIdentity> userIdentityRepository)
        {
            _userIdentityRepository = userIdentityRepository;
        }
        private async Task<UnifyResponseDto> BindAsync(string identityType, string name, string openId, long userId)
        {
            LinUserIdentity linUserIdentity = await _userIdentityRepository.Where(r => r.IdentityType == identityType && r.Credential == openId).FirstAsync();
            if (linUserIdentity == null)
            {
                var userIdentity = new LinUserIdentity(identityType, name, openId, DateTime.Now);
                userIdentity.CreateUserId = userId;
                await _userIdentityRepository.InsertAsync(userIdentity);
                return UnifyResponseDto.Success("绑定成功");
            }
            else
            {
                return UnifyResponseDto.Error("绑定失败,该用户已绑定其他账号");
            }
        }

        public abstract Task<long> SaveUserAsync(ClaimsPrincipal principal, string openId);

        public virtual async Task<UnifyResponseDto> BindAsync(ClaimsPrincipal principal, string identityType, string openId, long userId)
        {
            string nickname = principal.FindFirst(ClaimTypes.Name)?.Value;
            return await this.BindAsync(identityType, nickname, openId, userId);
        }

    }

我们拿Gitee登录为例，

public class GiteeOAuth2Service : OAuthService, IOAuth2Service
    {
        private readonly IUserRepository _userRepository;
        private readonly IAuditBaseRepository<LinUserIdentity> _userIdentityRepository;

        public GiteeOAuth2Service(IAuditBaseRepository<LinUserIdentity> userIdentityRepository, IUserRepository userRepository) : base(userIdentityRepository)
        {
            _userIdentityRepository = userIdentityRepository;
            _userRepository = userRepository;
        }
        public override async Task<long> SaveUserAsync(ClaimsPrincipal principal, string openId)
        {

            LinUserIdentity linUserIdentity = await _userIdentityRepository.Where(r => r.IdentityType == LinUserIdentity.Gitee && r.Credential == openId).FirstAsync();

            long userId = 0;
            if (linUserIdentity == null)
            {
                string email = principal.FindFirst(ClaimTypes.Email)?.Value;
                string name = principal.FindFirst(ClaimTypes.Name)?.Value;
                string nickname = principal.FindFirst(GiteeAuthenticationConstants.Claims.Name)?.Value;
                string avatarUrl = principal.FindFirst("urn:gitee:avatar_url")?.Value;
                string blogAddress = principal.FindFirst("urn:gitee:blog")?.Value;
                string bio = principal.FindFirst("urn:gitee:bio")?.Value;
                string htmlUrl = principal.FindFirst("urn:gitee:html_url")?.Value;

                LinUser user = new LinUser
                {
                    Active = UserActive.Active,
                    Avatar = avatarUrl,
                    LastLoginTime = DateTime.Now,
                    Email = email,
                    Introduction = bio + htmlUrl,
                    LinUserGroups = new List<LinUserGroup>()
                    {
                        new LinUserGroup()
                        {
                            GroupId = LinConsts.Group.User
                        }
                    },
                    Nickname = nickname,
                    Username = "",
                    BlogAddress = blogAddress,
                    LinUserIdentitys = new List<LinUserIdentity>()
                    {
                        new LinUserIdentity(LinUserIdentity.Gitee,name,openId,DateTime.Now)
                    }
                };
                await _userRepository.InsertAsync(user);
                userId = user.Id;
            }
            else
            {
                userId = linUserIdentity.CreateUserId;
            }

            return userId;
        }

    }

GitHub 登录，保存用户信息，伪代码。他们在获取用户信息中有些差别。

   public class GithubOAuth2Serivice : OAuthService, IOAuth2Service
    {
        private readonly IUserRepository _userRepository;
        private readonly IAuditBaseRepository<LinUserIdentity> _userIdentityRepository;

        public GithubOAuth2Serivice(IAuditBaseRepository<LinUserIdentity> userIdentityRepository, IUserRepository userRepository) : base(userIdentityRepository)
        {
            _userIdentityRepository = userIdentityRepository;
            _userRepository = userRepository;
        }

        public override async Task<long> SaveUserAsync(ClaimsPrincipal principal, string openId)
        {
            return userId;
        }
    }

依赖注入我们使用Autofac。同一个接口，可以 注入多个实现，通过Named区分。

builder.RegisterType<GithubOAuth2Serivice>().Named<IOAuth2Service>(LinUserIdentity.GitHub).InstancePerLifetimeScope();
builder.RegisterType<GiteeOAuth2Service>().Named<IOAuth2Service>(LinUserIdentity.Gitee).InstancePerLifetimeScope();
builder.RegisterType<QQOAuth2Service>().Named<IOAuth2Service>(LinUserIdentity.QQ).InstancePerLifetimeScope();

注入成功后，如何使用呢。我们通过 IComponentContext得到我们想要的对象。

回调登录保存用户信息，相当于生成一个账号。伪代码。

    public Oauth2Controller(IComponentContext componentContext)
    {
        _componentContext = componentContext;
    }

    [HttpGet("signin-callback")]
    public async Task<IActionResult> Home(string provider, string redirectUrl = "")
    {
        AuthenticateResult authenticateResult = await HttpContext.AuthenticateAsync(provider);

        IOAuth2Service oAuth2Service = _componentContext.ResolveNamed<IOAuth2Service>(provider);
        long id = await oAuth2Service.SaveUserAsync(authenticateResult.Principal, openIdClaim.Value);

        //...省略生成token的过程
        string token = _jsonWebTokenService.Encode(claims);

        return Redirect($"{redirectUrl}#login-result?token={token}");
    ｝

这里的Provider的值就是 LinUserIdentity.GitHub，一个字符串值。

    public class LinUserIdentity : FullAduitEntity<Guid>
    {
        public const string GitHub = "GitHub";
        public const string QQ = "QQ";
        public const string Gitee = "Gitee";
   }

源码

接口

• https://github.com/luoyunchong/lin-cms-dotnetcore/blob/master/src/LinCms.Application.Contracts/Cms/Users/IOAuth2Service.cs

抽象类

• https://github.com/luoyunchong/lin-cms-dotnetcore/blob/master/src/LinCms.Application.Contracts/Cms/Users/OAuthService.cs

实现

• https://github.com/luoyunchong/lin-cms-dotnetcore/blob/master/src/LinCms.Application/Cms/Users/GiteeOAuth2Service.cs
• https://github.com/luoyunchong/lin-cms-dotnetcore/blob/master/src/LinCms.Application/Cms/Users/GithubOAuth2Serivice.cs
• https://github.com/luoyunchong/lin-cms-dotnetcore/blob/master/src/LinCms.Application/Cms/Users/QQOAuth2Service.cs

调用

• https://github.com/luoyunchong/lin-cms-dotnetcore/blob/master/src/LinCms.Web/Controllers/Cms/Oauth2Controller.cs

接口注入

• https://github.com/luoyunchong/lin-cms-dotnetcore/blob/master/src/LinCms.Web/Startup/Configuration/ServiceModule.cs

总结

总结来说，我们干掉了switch case，好处是

• 实现了对扩展开放，对修改关闭，我们不需要修改现有的类，就能新增新的逻辑。
• 在整体上逻辑更清晰，而不是有一个需求，加一个接口，加一个实现，这样无脑操作。