No connection string could be found in the application config file - EF6

Question

Error:

No connection string named 'MediaRentalEntities' could be found in the application config file.

My config file:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
  </configSections>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.8" />
  </startup>
  <entityFramework>
    <providers>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
    </providers>
  </entityFramework>
  <connectionStrings>
    <add name="MediaRentalEntities" connectionString="metadata=res://*/Model1.csdl|res://*/Model1.ssdl|res://*/Model1.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=localhost;initial catalog=MediaRental;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework&quot;" providerName="System.Data.EntityClient" />
  </connectionStrings>
</configuration>

As you can see connection string is clearly there, it has been automatically generated. I can run the program but it constantly shows this error on error list and i'm unable to view designer.

I have found similar questions, but it was mostly about multiple projects, here i have only one solution and one project.

Edit

Constructor in DBContext:

public MediaRentalEntities()
        : base("name=MediaRentalEntities")
    {
}

Answer 1

change your constructor to be like

public MediaRentalEntities()
    : base("MediaRentalEntities")
{}