在运行时更改注入的对象

Question

我想要 IUserRepository 的多个实现，每个实现都可以使用 MongoDB 或任何 SQL 数据库的数据库类型。为此，我拥有具有连接字符串和其他租户配置的 ITenant 接口。租户被注入到 MongoDB 或任何 SQLDB 实现的 IUserRepository 中。我需要知道的是如何正确更改注入的存储库以根据租户选择数据库。

接口

public interface IUserRepository 
{
    string Login(string username, string password);
    string Logoff(Guid id);
}

public class User
{
    public Guid Id { get; set; }
    public string Username { get; set; }
    public string Password { get; set; }
    public string LastName { get; set; }
    public string FirstName { get; set; }

}

public interface ITenant
{
    string CompanyName { get; }
    string ConnectionString { get; }
    string DataBaseName { get; }
    string EncriptionKey { get; }

}

重要的是要知道租户 ID 已通过标头请求传递给 API

StartUp.cs

// set inject httpcontet to the tenant implemantion
services.AddTransient<IHttpContextAccessor, HttpContextAccessor>();

// inject tenant
services.AddTransient<ITenant, Tenant>();

// inject mongo repository but I want this to be programmatically
services.AddTransient<IUserRepository, UserMongoRepository>();

Mongo 实施示例

public class UserMongoRepository : IUserRepository
{

    protected ITenant Tenant 

    public UserMongoRepository(ITenant tenant) :
        base(tenant)
    {
        this.Tenant = tenant;
    }

    public string Login(string username, string password)
    {

        var query = new QueryBuilder<User>().Where(x => x.Username == username);
        var client = new MongoClient(this.Tenant.ConnectionString);var server = client.GetServer();
        var database =  client.GetServer().GetDatabase(this.Tenant.DataBaseName);
        var user = database.GetCollection<User>.FindAs<User>(query).AsQueryable().FirstOrDefault();

        if (user == null)
            throw new Exception("invalid username or password");

        if (user.Password != password)
            throw new Exception("invalid username or password");

         return "Sample Token";

    }

    public string Logoff(Guid id)
    {

        throw new NotImplementedException();
    }

}

租户

public class Tenant : ITenant
{

    protected IHttpContextAccessor Accesor;
    protected IConfiguration Configuration;

    public Tenant(IHttpContextAccessor accesor, IDBConfiguration config)
    {
        this.Accesor = accesor;
        this.Configuration = new Configuration().AddEnvironmentVariables();
        if (!config.IsConfigure)
            config.ConfigureDataBase();
    }


    private string _CompanyName;
    public string CompanyName
    {
        get
        {
            if (string.IsNullOrWhiteSpace(_CompanyName))
            {
                _CompanyName = this.Accesor.Value.Request.Headers["Company"];
                if (string.IsNullOrWhiteSpace(_CompanyName))
                    throw new Exception("Invalid Company");
            }
            return _CompanyName;
        }
    }

    private string _ConnectionString;
    public string ConnectionString
    {
        get
        {
            if (string.IsNullOrWhiteSpace(_ConnectionString))
            {
                _ConnectionString = this.Configuration.Get(this.CompanyName + "_" + "ConnectionString");
                if (string.IsNullOrWhiteSpace(_ConnectionString))
                    throw new Exception("Invalid ConnectionString Setup");
            }
            return _ConnectionString;
        }
    }

    private string _EncriptionKey;
    public string EncriptionKey
    {
        get
        {
            if (string.IsNullOrWhiteSpace(_EncriptionKey))
            {
                _EncriptionKey = this.Configuration.Get(this.CompanyName + "_" + "EncriptionKey");
                if (string.IsNullOrWhiteSpace(_EncriptionKey))
                    throw new Exception("Invalid Company Setup");
            }
            return _EncriptionKey;
        }
    }

    private string _DataBaseName;
    public string DataBaseName
    {
        get
        {
            if (string.IsNullOrWhiteSpace(_DataBaseName))
            {
                _DataBaseName = this.Configuration.Get(this.CompanyName + "_" + "DataBaseName");
                if (string.IsNullOrWhiteSpace(_DataBaseName))
                    throw new Exception("Invalid Company Setup");
            }
            return _DataBaseName;
        }
    }
}

控制器

public class UsersController : Controller
{
    protected IUserRepository DataService;

    public UsersController(IUserRepository dataService)
    {
        this.DataService = dataService;
    }

    // the controller implematation

}

Answer 1

您应该为IUserRepository 定义一个代理实现并将实际实现隐藏在此代理后面，并在运行时决定将调用转发到哪个存储库。例如：

public class UserRepositoryDispatcher : IUserRepository
{
    private readonly Func<bool> selector;
    private readonly IUserRepository trueRepository;
    private readonly IUserRepository falseRepository;

    public UserRepositoryDispatcher(Func<bool> selector,
        IUserRepository trueRepository, IUserRepository falseRepository) {
        this.selector = selector;
        this.trueRepository = trueRepository;
        this.falseRepository = falseRepository;
    }

    public string Login(string username, string password) {
        return this.CurrentRepository.Login(username, password);
    }

    public string Logoff(Guid id) {
        return this.CurrentRepository.Logoff(id);
    }

    private IRepository CurrentRepository {
        get { return selector() ? this.trueRepository : this.falseRepository;
    }
}

使用这个代理类，您可以轻松地创建一个运行时谓词来决定使用哪个存储库。例如：

services.AddTransient<IUserRepository>(c =>
    new UserRepositoryDispatcher(
        () => c.GetRequiredService<ITenant>().DataBaseName.Contains("Mongo"),
        trueRepository: c.GetRequiredService<UserMongoRepository>()
        falseRepository: c.GetRequiredService<UserSqlRepository>()));

Answer 2

您可以尝试注入工厂而不是实际的存储库。工厂将负责根据当前用户身份构建正确的存储库。

它可能需要更多样板代码，但它可以实现您想要的。一点点继承甚至可能使控制器代码更简单。