Why is there no connection?

Question

C++ / C#

DB on sqlExpress, connection in vs.

configuration file

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings>
    <add name="DefaultConnection" connectionString="Data Source=.\SQLEXPRESS;Initial Catalog=Proxy;Integrated Security=True"
        providerName="System.Data.SqlClient"/>
  </connectionStrings>
</configuration>

C#

string connectionString = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;
            Console.WriteLine(connectionString);

Why the exception

ConfigurationManager.ConnectionStrings["ConnectionName"].ConnectionString возвращает null?

Answer 1

Check the appsettings.json file. It is necessary to set the property "Always copy", or "Copy a later version"
RMB to file -> Properties