Detailed explanation of two ways to obtain connectionString

public static string connectionString = ["ConnectionString"].ConnectionString;

<connectionStrings>  

<add name="ConnectionString" connectionString="Data Source=localhost;Persist Security Info=True;User ID=***;Password=***;Unicode=True"  

  providerName="" />  

</connectionStrings>  

public static string connectionString = ["ConnectionString"]; 

<add key="ConnectionString" value="server=localhost;database=***;uid=sa;pwd=***"></add>  

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <appSettings><!--2.--><add key="ConnectionString" value="***"></add></appSettings>

    <connectionStrings/><!--1.-->
    <>
        <!-- 
            set up compilation debug="true" Debug symbols can be inserted
            In the compiled page。But because this will 
            Influence performance，Therefore, this value is only included during development 
            set up为 true。
        -->
        <compilation debug="false"></compilation>
        <!--
            pass <authentication> Sections can be configured  Used for 
            Identify the entry user
            Secure authentication mode。 
        -->
        <authentication mode="Windows" />
        <!--
            If an unprocessed error occurs during the execution of the request，
            则pass <customErrors> Sections can be configured相应的处理步骤。Specifically，
            开发人员pass该Sections can be configured
            To be displayed html Error page
            Instead of error stack trace。
        <customErrors mode="RemoteOnly" defaultRedirect="">
            <error statusCode="403" redirect="" />
            <error statusCode="404" redirect="" />
        </customErrors>
        -->
    </>
</configuration>

using ;using ;  //Note to add Oracle references; SqlServer comes with DataSet dataSet = new DataSet();List<ZHInfo> listzh = new List<ZHInfo>();string sql = "SELECT CODE,NAME,PHONE_NUMBER FROM ZHXX WHERE 1=1 AND ROWNUM<10 ";using (OracleConnection oracleConnection = new OracleConnection(connectionString))
{
();
OracleCommand selectCommand = new OracleCommand(sql, oracleConnection);
OracleDataAdapter oracleDataAdapter = new OracleDataAdapter(selectCommand);

(dataSet);
}
if ( &gt; 0 &amp;&amp; [0] != null &amp;&amp; [0]. &gt; 0)
{   //The connection is successful and data is returnedforeach (DataRow dr in [0].Rows)
{
(new ZHInfo { Code = dr["Code"].ToString(), Name = dr["Name"].ToString(), PublicNumber = dr["Phone_Number"].ToString() });
}
}

public class ZHInfo
 {
    public string Code { get; set; }
    public string Name { get; set; }
    public string PublicNumber { get; set; }
}