Visual Studio 2017在应用程序设置中找不到连接字符串

对于连接数据库和读取数据，我正在使用从Web.config文件读取连接字符串的数据集.一切都在Visual Studio 2013中正常工作.但是，当我在Visual Studio 2017中打开此项目时，无法进行配置.错误:

For connection database and reading data, I am using a dataset which read connection string from Web.config file. Everything working in Visual Studio 2013. But when I opened this project in Visual Studio 2017, I can't configure. It errors:

找不到连接字符串xxxx.在应用程序设置中找不到连接字符串，或者无法加载与该连接字符串关联的数据提供程序

Unable to find connection string xxxx. the connection string could not be found in application settings or the data provider associated with the connection string could not be loaded