通过读取 app.config 的连接字符串来连接数据库不用指定 ProviderName？

[Devin]

比如这 2 个
https://stackoverflow.com/questions/15360536/how-can-i-connect-c-sharp-with-db-with-app-config
https://stackoverflow.com/questions/8476103/accessing-database-connection-string-using-app-config-in-c-sharp-winform
都只是读取 connectionstring，没有提到 providerName

[hcymk2]

providerName 是可选属性，而且有默认值 System.Data.SqlClient