构造函数与 app.config 中的连接字符串？答案

【问题标题】：Connection string in constructor vs. app.config?构造函数与 app.config 中的连接字符串？
【发布时间】：2018-04-30 08:36:15
【问题描述】：

在我的上下文构造函数中引用配置值时，我没有遇到数据库连接问题：

public class MyDbContext : DbContext
{
    public MyDbContext ()
        : base("Name=Model1")
    {
    }
}

我的 App.config 连接字符串如下所示：

<connectionStrings>
    <add name="Model1"
         connectionString="data source=10.4.4.3;initial catalog=mydatabase;persist security info=True;user id=myuser;password=mypass;MultipleActiveResultSets=True;App=EntityFramework"
         providerName="System.Data.SqlClient" />
  </connectionStrings>

但是，当我像这样对连接进行硬编码时：

public class MyDbContext : DbContext
{
    public MyDbContext ()
        : base(@"data source=10.4.4.3;initial catalog=mydatabase;persist security info=True;user id=myuser;password=mypass;MultipleActiveResultSets=True;App=EntityFramework")
    {
    }
}

我得到的例外是：

{System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Configuration.ConfigurationErrorsException: Configuration system failed to initialize ---> System.Configuration.ConfigurationErrorsException: Unrecognized element. (C:\ProgramData\SF\vm0\Fabric\work\Applications\abc.API.ProdAndPrice.O720.ProdLinesType_App285\ComponentsPkg.Code.1.0.0\Components.exe.Config line 38)
   at System.Configuration.ConfigurationSchemaErrors.ThrowIfErrors(Boolean ignoreLocal)
   at System.Configuration.BaseConfigurationRecord.ThrowIfParseErrors(ConfigurationSchemaErrors schemaErrors)
   at System.Configuration.ClientConfigurationSystem.EnsureInit(String configKey)
   --- End of inner exception stack trace ---
   at System.Configuration.ConfigurationManager.PrepareConfigSystem()
   at System.Configuration.ConfigurationManager.GetSection(String sectionName)
   at System.Configuration.PrivilegedConfigurationManager.GetSection(String sectionName)
   at System.Diagnostics.DiagnosticsConfiguration.GetConfigSection()
   at System.Diagnostics.DiagnosticsConfiguration.Initialize()
   at System.Diagnostics.DiagnosticsConfiguration.get_IndentSize()
   at System.Diagnostics.TraceInternal.InitializeSettings()
   at System.Diagnostics.TraceInternal.get_Listeners()
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Reflection.RuntimePropertyInfo.GetValue(Object obj, Object[] index)
   at Microsoft.Owin.Hosting.Utilities.SettingsLoader.FromConfigImplementation..ctor()
   at Microsoft.Owin.Hosting.Utilities.SettingsLoader.<LoadFromConfig>b__0()
   at System.Threading.LazyInitializer.EnsureInitializedCore[T](T& target, Func`1 valueFactory)
   at Microsoft.Owin.Hosting.Utilities.SettingsLoader.LoadFromConfig(IDictionary`2 settings)
   at Microsoft.Owin.Hosting.Engine.StartContext..ctor(StartOptions options)
   at Microsoft.Owin.Hosting.WebApp.StartImplementation(IServiceProvider services, StartOptions options, Action`1 startup)
   at Microsoft.Owin.Hosting.WebApp.Start(String url, Action`1 startup)
   at Components.OwinCommunicationListener.OpenAsync(CancellationToken cancellationToken) in F:\TFS\ooo720 Res\ooo720\DEV\Source\enterprise\abc.API.ProdAndPrice.O720.ProdLines\Components\OwinCommunicationListener.cs:line 78
   at Microsoft.ServiceFabric.Services.Runtime.StatelessServiceInstanceAdapter.<OpenCommunicationListenersAsync>d__19.MoveNext()}

我做错了什么？为什么连接失败？

【问题讨论】：

如果您在第一个代码 sn-p 中注意到您正在执行此操作 base("Name=Model1")。您正在为代码提供要在 app.config 中查找的连接字符串的名称。您最后剪断的代码导致Unrecognized element 异常，因此当您传入整个连接字符串时，它会尝试将其作为连接字符串的名称来查找，但该名称不存在。
那么，第一个例子是有效的，对吧？为什么不这样做呢？
我感觉异常与您的上下文无关，您只是在从那里删除连接字符串时损坏了您的 app.config。
@Evk 这正是答案，谢谢

标签： c# .net asp.net-web-api2 visual-studio-2017 azure-service-fabric

【解决方案1】：

当你为它分配一个键而不使用它并且只是在构造函数中传递连接字符串时，你不需要 app.config 中的连接字符串

【讨论】：