一直以来都在学习中，所以也没有什么好文章献给大家，这次小弟也是来提问的，Dudu觉得不合适可以从首页撤掉。不过本人认为让更多的人看到问题也是不错的。
问题如下：
    建立了Book数据库，库中有三张表Orders，Products，Remarks。其中Orders的字段Oid是Products字段Poid的主键，意思是这两张表组成了主外键关系。Remarks是一张独立的表。利用Linq To SQL设计器生成了三张表的实体类。并将三个实体类暴露给客户端（[DataContract]）.代码如下：

Orders类：

Code
  1[Table(Name="dbo.orders")]
  2    [DataContract(Name = "Orders", Namespace = "http://www.lgx.OrderLinq")]
  3    public partial class order : INotifyPropertyChanging, INotifyPropertyChanged
  4    {
  5        
  6        private static PropertyChangingEventArgs emptyChangingEventArgs = new PropertyChangingEventArgs(String.Empty);
  7        
  8        private int _oid;
  9        
 10        private System.Nullable<decimal> _totalPrice;
 11        
 12        private System.DateTime _odate;
 13        
 14        private EntitySet<product> _products;
 15        
 16    Extensibility Method Definitions#region Extensibility Method Definitions
 17    partial void OnLoaded();
 18    partial void OnValidate(System.Data.Linq.ChangeAction action);
 19    partial void OnCreated();
 20    partial void OnoidChanging(int value);
 21    partial void OnoidChanged();
 22    partial void OntotalPriceChanging(System.Nullable<decimal> value);
 23    partial void OntotalPriceChanged();
 24    partial void OnodateChanging(System.DateTime value);
 25    partial void OnodateChanged();
 26    #endregion
 27        
 28        public order()
 29        {
 30            this._products = new EntitySet<product>(new Action<product>(this.attach_products), new Action<product>(this.detach_products));
 31            OnCreated();
 32        }
 33        
 34        [Column(Storage="_oid", AutoSync=AutoSync.OnInsert, DbType="Int NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true)]
 35        [DataMember(Order=0)]
 36        public int oid
 37        {
 38            get
 39            {
 40                return this._oid;
 41            }
 42            set
 43            {
 44                if ((this._oid != value))
 45                {
 46                    this.OnoidChanging(value);
 47                    this.SendPropertyChanging();
 48                    this._oid = value;
 49                    this.SendPropertyChanged("oid");
 50                    this.OnoidChanged();
 51                }
 52            }
 53        }
 54        
 55        [Column(Storage="_totalPrice", DbType="Decimal(18,3)")]
 56        [DataMember(Order = 1)]
 57        public System.Nullable<decimal> totalPrice
 58        {
 59            get
 60            {
 61                return this._totalPrice;
 62            }
 63            set
 64            {
 65                if ((this._totalPrice != value))
 66                {
 67                    this.OntotalPriceChanging(value);
 68                    this.SendPropertyChanging();
 69                    this._totalPrice = value;
 70                    this.SendPropertyChanged("totalPrice");
 71                    this.OntotalPriceChanged();
 72                }
 73            }
 74        }
 75        
 76        [Column(Storage="_odate", DbType="DateTime NOT NULL")]
 77        [DataMember(Order = 2)]
 78        public System.DateTime odate
 79        {
 80            get
 81            {
 82                return this._odate;
 83            }
 84            set
 85            {
 86                if ((this._odate != value))
 87                {
 88                    this.OnodateChanging(value);
 89                    this.SendPropertyChanging();
 90                    this._odate = value;
 91                    this.SendPropertyChanged("odate");
 92                    this.OnodateChanged();
 93                }
 94            }
 95        }
 96        
 97        [Association(Name="order_product", Storage="_products", OtherKey="poid")]
 98        [DataMember(Order = 3)]
 99        public EntitySet<product> products
100        {
101            get
102            {
103                return this._products;
104            }
105            set
106            {
107                this._products.Assign(value);
108            }
109        }
110        
111        public event PropertyChangingEventHandler PropertyChanging;
112        
113        public event PropertyChangedEventHandler PropertyChanged;
114        
115        protected virtual void SendPropertyChanging()
116        {
117            if ((this.PropertyChanging != null))
118            {
119                this.PropertyChanging(this, emptyChangingEventArgs);
120            }
121        }
122        
123        protected virtual void SendPropertyChanged(String propertyName)
124        {
125            if ((this.PropertyChanged != null))
126            {
127                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
128            }
129        }
130        
131        private void attach_products(product entity)
132        {
133            this.SendPropertyChanging();
134            entity.order = this;
135        }
136        
137        private void detach_products(product entity)
138        {
139            this.SendPropertyChanging();
140            entity.order = null;
141        }
142    }

Products类：

Code
  1[Table(Name="dbo.products")]
  2    [DataContract(Name = "Products", Namespace = "http://www.lgx.OrderLinq")]
  3    public partial class product : INotifyPropertyChanging, INotifyPropertyChanged
  4    {
  5        
  6        private static PropertyChangingEventArgs emptyChangingEventArgs = new PropertyChangingEventArgs(String.Empty);
  7        
  8        private int _pid;
  9        
 10        private int _poid;
 11        
 12        private string _pName;
 13        
 14        private decimal _price;
 15        
 16        private System.DateTime _pdate;
 17        
 18        private EntityRef<order> _order;
 19        
 20    Extensibility Method Definitions#region Extensibility Method Definitions
 21    partial void OnLoaded();
 22    partial void OnValidate(System.Data.Linq.ChangeAction action);
 23    partial void OnCreated();
 24    partial void OnpidChanging(int value);
 25    partial void OnpidChanged();
 26    partial void OnpoidChanging(int value);
 27    partial void OnpoidChanged();
 28    partial void OnpNameChanging(string value);
 29    partial void OnpNameChanged();
 30    partial void OnpriceChanging(decimal value);
 31    partial void OnpriceChanged();
 32    partial void OnpdateChanging(System.DateTime value);
 33    partial void OnpdateChanged();
 34    #endregion
 35        
 36        public product()
 37        {
 38            this._order = default(EntityRef<order>);
 39            OnCreated();
 40        }
 41        
 42        [Column(Storage="_pid", AutoSync=AutoSync.OnInsert, DbType="Int NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true)]
 43        [DataMember(Order=0)]
 44        public int pid
 45        {
 46            get
 47            {
 48                return this._pid;
 49            }
 50            set
 51            {
 52                if ((this._pid != value))
 53                {
 54                    this.OnpidChanging(value);
 55                    this.SendPropertyChanging();
 56                    this._pid = value;
 57                    this.SendPropertyChanged("pid");
 58                    this.OnpidChanged();
 59                }
 60            }
 61        }
 62        
 63        [Column(Storage="_poid", DbType="Int NOT NULL")]
 64        [DataMember(Order = 1)]
 65        public int poid
 66        {
 67            get
 68            {
 69                return this._poid;
 70            }
 71            set
 72            {
 73                if ((this._poid != value))
 74                {
 75                    if (this._order.HasLoadedOrAssignedValue)
 76                    {
 77                        throw new System.Data.Linq.ForeignKeyReferenceAlreadyHasValueException();
 78                    }
 79                    this.OnpoidChanging(value);
 80                    this.SendPropertyChanging();
 81                    this._poid = value;
 82                    this.SendPropertyChanged("poid");
 83                    this.OnpoidChanged();
 84                }
 85            }
 86        }