configuration.GetConnectionString（“ MyConn”）获得空值？ [英] configuration.GetConnectionString("MyConn") got null value?

问题描述

在以下控制台应用程序（.Net core 2.0）中， conn 具有空值。

In the following console application (.Net core 2.0), the conn got a null value.

var services = new ServiceCollection();

IConfigurationRoot configuration = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddXmlFile("App.config", optional: false).Build();

services.AddSingleton(configuration);

var conn = configuration.GetConnectionString("MyConn"); // conn is null

以下是App.config。

The following is App.config.

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings>
    <add name="MyConn" connectionString="....." />
  </connectionStrings>
  <Settings>
    <Name>Test</Name>
  </Settings>
</configuration>

有些代码可以获取的值（测试） 设置的名称成功。

There is some code which can get the value ("Test") of Name of the Settings successfully.

更新：

在分配 conn 之后，我具有以下代码来获取< XML部分的Settings> 部分，它可以获取值 Test。

Right after the assignment of conn, I have the following code to get <Settings> section of the XML part and it can get the value "Test".

var myOptions = new MyOptions();
configuration.GetSection("Settings").Bind(myOptions);

推荐答案

请参见 GetConnectionString 只是扩展方法只需执行以下操作：

See, GetConnectionString is just an extension method that simply do the following:

public static string GetConnectionString(this IConfiguration configuration, string name)
{
    return configuration?.GetSection("ConnectionStrings")?[name];
}

如果在调试过程中检查了 Data 在配置中。提供者对于
，您会发现以下键/值：

If during debugging you check Data in configuration.Providers for you will find the following keys/values among others:

key: "connectionStrings:add:MyConn:name" | value: "MyConn"
key: "connectionStrings:add:MyConn:connectionString" | value: "....."

这就是为什么您得到的原因空值。

That's actually why you got a null value.

因此，使用当前的XML结构，您可以轻松地做到： p>

So with the current XML structure, you can simply do:

var connString = configuration.GetValue<string>("connectionStrings:add:MyConn:connectionString", string.Empty);

或将XML修改为

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings>
    <MyConn>conn_string_here</MyConn>
  </connectionStrings>
</configuration>

并使用

var conn = configuration.GetConnectionString("MyConn");
// conn value will be "conn_string_here"

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