如何先用实体框架代码删除多对多自动生成的表

我有3个实体 产品 , 供应商 合同

为了在这个多对多关系上添加额外属性,我创建了第三个实体 供应商产品

此外,我还创建了另一个实体 该公司持有供应商的产品;合同。当我为测试播种一些数据时,我可以观察到ProductSupplierForContract没有该产品&供应商Id值,而它们存在于我的ProductForSupplier实体中,但Id具有记录的ProductForSupplierId。

既然我有保存这两个值的表的Id,如何删除表ProductSupplierForContract中的这两个属性?

实体:

public class Product : BaseEntity // BaseEntity just holds an Id and a date
{
    public ICollection<ProductSupplierForContract> ProductSupplierForContracts { get; set; }
    public ICollection<ProductForSupplier> ProductForSuppliers { get; set; }
}

public class Supplier : BaseEntity
{
    public ICollection<ProductForSupplier> ProductForSuppliers { get; set; }
    public ICollection<ProductSupplierForContract> ProductSupplierForContracts { get; set; }
} 

public class Contract : BaseEntity
{
    public ICollection<ProductSupplierForContract> ProductSupplierForContracts { get; set; }
}

public class ProductForSupplier:BaseEntity
{
    public string ProductNumber{ get; set; }

    [Required]
    public Product Product { get; set; }

    [Required]
    public Supplier Supplier { get; set; }
}

public class ProductSupplierForContract: BaseEntity
{
    [Required]
    public ProductForSupplier ProductForSupplier { get; set; }

    [Required]
    public Contract Contract { get; set; }
}

播种法

 protected override void Seed(TestDbContext context)
 {
     Supplier supplier1 = new Supplier("Microsoft");
     context.Suppliers.Add(supplier1);         

     Product product1 = new Product("test product 1");
     context.Products.Add(product1);

     Contract contract = new Contract("Contract 1");
     context.Contracts.Add(contract);

     ProductForSupplier pfs = new ProductForSupplier("123productNumber");
     pfs.Supplier = supplier1;
     pfs.Product = product1;        
     context.ProductForSuppliers.Add(pfs);

     ProductSupplierForContract psfc = new ProductSupplierForContract(pfs, contract);
     context.ProductSupplierForContracts.Add(psfc);

     base.Seed(context);
 }