c# - 从不同项目的 appsettings.json 中读取多个连接字符串

Question

我正在使用 .Net core v 2.1 来创建网络 API。我的解决方案包含不同的项目层(BLL、DAL、Common 等)并且主项目中有一个 appsettings.json 文件。我的 appsettings.json 文件中有多个连接字符串，我想根据 Controller 中传递的参数选择连接字符串。

这是项目结构和代码:

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);
}

例如。我正在传递 conn = "CON1"

AccountController.cs

[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;
    }
}

2)dal层

AccountDL.cs

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

3) 公共(public)配置层

AppConfiguration.cs

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;
        }
    }
}

现在我将使用此 dbConn 连接对象进行进一步处理，但我收到 System.NullReferenceException: 'Object reference not set to an instance of an object.' 的异常。

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，但在重构我的项目后，我想在不同的项目(即 DAL)中使用此连接，我如何获取连接字符串基于不同项目中的参数？提前谢谢你。

Answer 1

因此，您可以通过 GetConnection() 方法从 appsettings.json 文件访问连接字符串值 -

AppConfiguration.cs

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.cs Controller 中，您需要在该 Controller 的构造函数中注入(inject)IConfiguration对象的依赖。

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);
    }
}