localdb

   <connectionStrings>
 -    <add name="default" connectionString="Data Source=.; Integrated Security=True; Initial Catalog=OSharp.Default; Pooling=True; MultipleActiveResultSets=True;" providerName="System.Data.SqlClient" />
 -    
 -    <!--<add name="mysql-default" connectionString="Server=localhost; Database=OSharp.Default; Uid=gmf; Pwd=31529019; charset=utf8;" providerName="MySql.Data.MySqlClient" />-->
 -    
 +    <!--mssql-->
 +    <!--<add name="default" providerName="System.Data.SqlClient" connectionString="Data Source=.; Integrated Security=True; Initial Catalog=OSharp.Default; Pooling=True; MultipleActiveResultSets=True;" />-->
 +    <!--localdb-->
 +    <add name="default" providerName="System.Data.SqlClient" connectionString="Data Source=(localdb)MSSQLLocalDB;Integrated Security=True;Initial Catalog=OSharp.Default;AttachDBFilename=|DataDirectory|OSharp.Default.mdf;" />
 +    <!--mysql-->
 +    <!--<add name="mysql-default" providerName="MySql.Data.MySqlClient" connectionString="Server=localhost; Database=OSharp.Default; Uid=gmf; Pwd=31529019; charset=utf8;" />-->
    </connectionStrings>