SPMetal generate code: EntityList not EntityList in data context class?

I create and deploy custom list by visual studio 2010. I have 3 file: Instance, element and schema. Then I used SPMetal to generate code.

[Microsoft.SharePoint.Linq.ListAttribute(Name="Currency")]
public Microsoft.SharePoint.Linq.EntityList<Item> Currency
{
 get {
 return this.GetList<Item>("Currency");
}
}

If I create custom list(Currency) by sharepoint, SPMetal will generate code below. What should I edit in my xml file(instance, element, schema) so that SPMetal gen to:

[Microsoft.SharePoint.Linq.ListAttribute(Name="Currency")]
public Microsoft.SharePoint.Linq.EntityList<Currency> Currency
{
 get {
 return this.GetList<Currency>("Currency");
}
}