C# 从不同项目的appsettings.json读取多个连接字符串

我正在使用.NETCore2.1创建WebAPI。我的解决方案包含不同的项目层（BLL、DAL、Common等），主项目中有一个appsettings.json文件。我的appsettings.json文件中有多个连接字符串，我希望根据传入控制器的参数选择连接字符串

public class AccountController
{
    public IConfiguration _configuration { get; }

    public AccountController(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    [HttpPost]
    [Route("CreateUser")]
    public IActionResult CreateUser(string conn, string username)
    {
        try
        {
            AccountDL objAccountDL = new AccountDL(_configuration); //call account data layer
            objAccountDL.CreateUser(conn, username); //conn = "CON1"
            return Ok();
        }
        catch(Exception ex)
        {
            throw ex;
        }
    }
}

以下是项目结构和代码：

1）api层

appsettings.json

"ConnectionStrings": {
    "CON1": "con1 connectionstring",
    "CON2": "con2 connectionstring",
    "CON3": "con3 connectionstring"
},

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<IConfiguration>(Configuration);
}

[HttpPost]
[Route("CreateUser")]
public IActionResult CreateUser(string conn, string username)
{
    try
    {
        AccountDL objAccountDL = new AccountDL(); //call account data layer
        objAccountDL.CreateUser(conn, username); //conn = "CON1"
        return Ok();
    }
    catch(Exception ex)
    {
        throw ex;
    }
}

public class AccountDL
{
    IConfiguration _configuration;
    OracleConnection _oracleConnection;
    public string CreateUser(string conn, string username)
    {
        AppConfiguration appConfg = new AppConfiguration(_configuration);   
        _oracleConnection = appConfg.GetConnection(conn);
    }
}

public class AppConfiguration
{
    public IConfiguration _configuration { get; }

    public AppConfiguration(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public OracleConnection GetConnection(string conn)
    {
        try
        {
            string connectionString = _configuration.GetSection("ConnectionStrings").GetSection(conn).Value;
            OracleConnection dbConn = new OracleConnection(connectionString);
            return dbConn;
        }
        catch(Exception ex)
        {
            throw ex;
        }
    }
}

public OracleConnection GetConnection(string conn)
{
    try
    {
        string connectionString = _configuration["ConnectionStrings:" + conn];
        OracleConnection dbConn = new OracleConnection(connectionString);
        return dbConn;
    }
    catch(Exception ex)
    {
        throw ex;
    }
}

2）dal层

AccountDL.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<IConfiguration>(Configuration);
}

[HttpPost]
[Route("CreateUser")]
public IActionResult CreateUser(string conn, string username)
{
    try
    {
        AccountDL objAccountDL = new AccountDL(); //call account data layer
        objAccountDL.CreateUser(conn, username); //conn = "CON1"
        return Ok();
    }
    catch(Exception ex)
    {
        throw ex;
    }
}

public class AccountDL
{
    IConfiguration _configuration;
    OracleConnection _oracleConnection;
    public string CreateUser(string conn, string username)
    {
        AppConfiguration appConfg = new AppConfiguration(_configuration);   
        _oracleConnection = appConfg.GetConnection(conn);
    }
}

public class AppConfiguration
{
    public IConfiguration _configuration { get; }

    public AppConfiguration(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public OracleConnection GetConnection(string conn)
    {
        try
        {
            string connectionString = _configuration.GetSection("ConnectionStrings").GetSection(conn).Value;
            OracleConnection dbConn = new OracleConnection(connectionString);
            return dbConn;
        }
        catch(Exception ex)
        {
            throw ex;
        }
    }
}

public OracleConnection GetConnection(string conn)
{
    try
    {
        string connectionString = _configuration["ConnectionStrings:" + conn];
        OracleConnection dbConn = new OracleConnection(connectionString);
        return dbConn;
    }
    catch(Exception ex)
    {
        throw ex;
    }
}

3）公共配置层

AppConfiguration.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<IConfiguration>(Configuration);
}

[HttpPost]
[Route("CreateUser")]
public IActionResult CreateUser(string conn, string username)
{
    try
    {
        AccountDL objAccountDL = new AccountDL(); //call account data layer
        objAccountDL.CreateUser(conn, username); //conn = "CON1"
        return Ok();
    }
    catch(Exception ex)
    {
        throw ex;
    }
}

public class AccountDL
{
    IConfiguration _configuration;
    OracleConnection _oracleConnection;
    public string CreateUser(string conn, string username)
    {
        AppConfiguration appConfg = new AppConfiguration(_configuration);   
        _oracleConnection = appConfg.GetConnection(conn);
    }
}

public class AppConfiguration
{
    public IConfiguration _configuration { get; }

    public AppConfiguration(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public OracleConnection GetConnection(string conn)
    {
        try
        {
            string connectionString = _configuration.GetSection("ConnectionStrings").GetSection(conn).Value;
            OracleConnection dbConn = new OracleConnection(connectionString);
            return dbConn;
        }
        catch(Exception ex)
        {
            throw ex;
        }
    }
}

public OracleConnection GetConnection(string conn)
{
    try
    {
        string connectionString = _configuration["ConnectionStrings:" + conn];
        OracleConnection dbConn = new OracleConnection(connectionString);
        return dbConn;
    }
    catch(Exception ex)
    {
        throw ex;
    }
}

现在，我将使用此dbConn连接对象进行进一步处理，但得到的异常为System.NullReferenceException:“对象引用未设置为对象的实例。”

如果我在同一个api层中尝试所有这些，那么我将根据传递的参数获取连接字符串，但在重新构造我的项目后，我希望在不同的项目（即DAL）中使用此连接，如何根据不同项目中的参数获取连接字符串？

---

提前感谢。

因此，您可以从appsettings.json文件中访问连接字符串值，以获得类似以下方法的

GetConnection（）-

AppConfiguration.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<IConfiguration>(Configuration);
}

[HttpPost]
[Route("CreateUser")]
public IActionResult CreateUser(string conn, string username)
{
    try
    {
        AccountDL objAccountDL = new AccountDL(); //call account data layer
        objAccountDL.CreateUser(conn, username); //conn = "CON1"
        return Ok();
    }
    catch(Exception ex)
    {
        throw ex;
    }
}

public class AccountDL
{
    IConfiguration _configuration;
    OracleConnection _oracleConnection;
    public string CreateUser(string conn, string username)
    {
        AppConfiguration appConfg = new AppConfiguration(_configuration);   
        _oracleConnection = appConfg.GetConnection(conn);
    }
}

public class AppConfiguration
{
    public IConfiguration _configuration { get; }

    public AppConfiguration(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public OracleConnection GetConnection(string conn)
    {
        try
        {
            string connectionString = _configuration.GetSection("ConnectionStrings").GetSection(conn).Value;
            OracleConnection dbConn = new OracleConnection(connectionString);
            return dbConn;
        }
        catch(Exception ex)
        {
            throw ex;
        }
    }
}

public OracleConnection GetConnection(string conn)
{
    try
    {
        string connectionString = _configuration["ConnectionStrings:" + conn];
        OracleConnection dbConn = new OracleConnection(connectionString);
        return dbConn;
    }
    catch(Exception ex)
    {
        throw ex;
    }
}

在AccountController.cscontroller中，需要将
IConfiguration
对象的依赖项注入该控制器的构造函数中

public class AccountController
{
    public IConfiguration _configuration { get; }

    public AccountController(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    [HttpPost]
    [Route("CreateUser")]
    public IActionResult CreateUser(string conn, string username)
    {
        try
        {
            AccountDL objAccountDL = new AccountDL(_configuration); //call account data layer
            objAccountDL.CreateUser(conn, username); //conn = "CON1"
            return Ok();
        }
        catch(Exception ex)
        {
            throw ex;
        }
    }
}

因此，您还需要修改AccountDL.cs类。您需要在构造函数或方法参数中传递该对象

public class AccountDL
{
    IConfiguration _configuration;
    OracleConnection _oracleConnection;

    public AccountDL(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    public string CreateUser(string conn, string username)
    {
        AppConfiguration appConfg = new AppConfiguration(_configuration);   
        _oracleConnection = appConfg.GetConnection(conn);
    }
}

@我已经修改了我的答案。请检查一下，让我知道。