如何控制EF插入数据库

我有3个表Goods, Producer, Categories。Producer和Categories与Goods有一对多的关系，我有一个通用的插入方法，代码如下所示。

问题是，当我试图插入商品列表时，第一个商品被正确添加，但如果下一个具有相同id的类别，则抛出关于主键的异常。

但是我想控制插入之类的东西，每次插入表Categories和Producer之前检查，如果行已经存在，只需更新它，例如或跳过。

带有模型和泛型插入的代码:

public class Good
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
    public virtual Category Category { get; set; }
    public virtual Producer Producer { get; set; }
    public override string ToString()
    {
        return Id + "/" + Name + "/" + Price + "/" + Category.Name + "/" + Producer.Name + "/" + Producer.Country;
    }
}
public class Producer
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int Id { get; set; }
    public string Name { get; set; }
    public string Country { get; set; }
    public virtual ICollection<Good> Goods { get; set; }
    public override string ToString()
    {
        return Id + "/" + Name + "/" + Country;
    }
}
public class Category
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Good> Goods { get; set; }
    public override string ToString()
    {
        return Id + "/" + Name;
    }
}
public void AddList(List<T> collection, DbContext GoodsContext)
{
        foreach (var item in collection)
        {
            GoodsContext.Set<T>().Add(item);
            GoodsContext.SaveChanges();
        }
}

 foreach (var item in collection)
 {
        // This will set the state of the main entity and all of it's navigational 
        // properties as `Added` or `Modified`.
        GoodsContext.InsertOrUpdateGraph(item);
        GoodsContext.SaveChanges();
        GoodsContext.Entry(item).State = EntityState.Detached;
 }