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c# - 如何访问连接字符串并连接到数据库

问题描述

所以我正在做一个涉及外部 API 和数据库的项目。此 API 使用称为 Add In 的 API 特定项目类型，并编译为库，然后添加到 API 的源程序中。这样，我可以在程序的 Add in 中创建自己创建的“操作”，并从 MVC Web 项目远程调用它们。此操作还包含与更新服务器上上传的数据库相关的代码。当我尝试远程调用此操作时，我会在添加了插件的应用程序中收到此错误：

A network-related or instance-specific error occurred while establishing a connection to SQL server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

我得到了导师的帮助，并对 Add Ins app.config 中的连接字符串进行了故障排除。它被验证是正确的（我可以直接从 web MVC 项目访问数据库）。我尝试读取var connectionString = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;项目中使用的连接字符串，但找不到。调用该操作时，我得到一个空对象引用错误。

这是我的加载项的应用程序配置：

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <connectionStrings>
    <add name="DefaultConnection" connectionString="Data Source=PROD4W\PROD4W;Initial Catalog=EplanInterfaceDb;user id = SomeID; password=SomePassword;Integrated Security=False" providerName="System.Data.SqlClient"/>
  </connectionStrings>
</configuration>

这是我的 add In 项目中与数据库相关的代码：

//Here is where my mentor tried to pull the connection string from the //app.config.This is where the object reference error
var connectionString = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;
//Output the connection string to the screen on outside app
new Decider().Decide(EnumDecisionType.eOkDecision, "Connection: " + connectionString, "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK);
//Access the database and add a test
using (var context = new DataContext())
  {
    //Throws network related error mentioned above
    context.Macros.Add(new Macro { Name = "test" });                    
    context.SaveChanges();
    //Output to the screen if the savechanges was successful
    new Decider().Decide(EnumDecisionType.eOkDecision, "Save Changes Called ", "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK);

  }

标签： c#sql-serverentity-frameworkapiconnection-string

解决方案

使用 Mason 在下面推荐的内容，您可以简单地对连接字符串进行硬编码，而不是从 app.config 中提取它（如果它给您带来问题）。这是一个示例：

var connectionString = "Hard code connection string";
//Make sure your DataContext has a constructor that takes in a connection string
using (var context = new DataContext(connectionString)) 
  {
    context.Macros.Add(new Macro { Name = "test" });                    
    context.SaveChanges();
    //Output to the screen if the savechanges was successful
    new Decider().Decide(EnumDecisionType.eOkDecision, "Save Changes Called ", "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK);
  }

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