I have the following models:
class Item
{
    public ICollection<string> GroupIds { get; set; }
    // Introduced for EF only
    public ICollection<Group> Groups { get; set; }
}
class Group
{
    public ICollection<string> ItemIds { get; set; }
    // Introduced for EF only
    public ICollection<Item> Items { get; set; }
}
class Store
{
    public ICollection<Item> Items { get; set; }
    public ICollection<Group> Groups { get; set; }
}
Store contains all Items and all Groups, but every Item may be related with one or multiple Group and every Group may be related with one or multiple Item.
How I can configure many-to-many relationship between Item and Group to load only GroupIds and ItemIds, but not objects itself?
