有关LINQ to SQL的简单问题

[Table(Name = \"Rates\")]
public class Rate
{
    private EntityRef<Product> _Product;

    [Column(IsPrimaryKey = true)]
    public String RateID 
    { get; set; }
    [Column]
    public String ProductID 
    { get; set; }
    [Column]
    public Double VolumeInTons 
    { get; set; }
    [Column]
    public Decimal Volume 
    { get; set; }
    [Column]
    public Decimal Cost 
    { get; set; }
    [Column]
    public UInt32 Year 
    { get; set; }

    [Association(Storage = \"_Product\", OtherKey = \"ProductID\")]
    public Product Product
    {
        get { return this._Product.Entity; }
        set { this._Product.Entity = value; }
    }
} 

[Table(Name=\"Products\")]
public class Product
{
    private EntitySet<Rate> _Rates;

    [Column(IsPrimaryKey= true)]
    public String ProductID
    { get; set; }
    [Column]
    public String Name
    { get; set; }
    [Column]
    public String Category
    { get; set; }

    [Association(Storage=\"_Rates\", OtherKey=\"ProductID\")]
    public EntitySet<Rate> Rates
    {
        get { return this._Rates; }
        set { this._Rates.Assign(value); }
    }
}

LINQ to SQL