04创建实体模型

在使用LINQ to SQL之前，除了要属性LINQ的语法，还要创建实体模型。

1 创建Project

新建控制台项目，命名为LinqConsoleApp

2 添加DLL和Namepace

1.添加System.Data.Linq.dll

2.using System.Data.Linq;

3.using System.Data.Linq.Mapping;

3 将类映射到数据库表

以NorthWind为例，建立Customer和Order实体及其联系。

3.1创建Order类

[Table(Name = "Orders")]
    public class Order
    {
        private int _OrderID = 0;
        private string _CustomerID;
        private EntityRef<Customer> _Customer;

        public Order()
        {
            this._Customer = new EntityRef<Customer>();
        }

        
        /// <summary>
        /// OrderID 属性
        /// </summary>
        /// <remarks>
        /// DbType：数据表字段的数据类型
        /// IsDbGenerated：是否自动增长
        /// </remarks>
        [Column(Storage = "_OrderID", DbType = "Int NOT NULL IDENTITY",
        IsPrimaryKey = true, IsDbGenerated = true)]
        public int OrderID
        {
            get { return this._OrderID; }
        }

        [Column(Storage = "_CustomerID", DbType = "NChar(5)")]
        public string CustomerID
        {
            get { return this._CustomerID; }
            set { this._CustomerID = value; }
        }


        //------------ 定义联系 ------------------------       
        /// <summary>
        /// 导航到 Customer
        /// </summary>
        /// <remarks>
        /// 使用 CustomerID 关联到 Customer ThisKey
        /// Order的外键(CustomerID) 在 Customer 是主键，所以使用 ThisKey
        /// </remarks>
        [Association(Storage = "_Customer", ThisKey = "CustomerID")]
        public Customer Customer
        {
            get { return this._Customer.Entity; }
            set { this._Customer.Entity = value; }
        }
    }

3.2创建Customer类

 /// <summary>
    /// 客戶類
    /// </summary>
    /// <remarks>
    /// Table的Name屬性指定對應的數據庫表名
    /// </remarks>
    [Table(Name = "Customers")]
    public class Customer
    {
        private string _CustomerID;

        /// <summary>
        /// 類成員之屬性對應到數據庫表的字段
        /// 默認使用屬性，可以使用Name指定，並且Name的值必須是數據庫表存在的字段名。
        /// IsPrimaryKey：是否為主鍵
        /// Storage：儲存值的類成員之字段
        /// </summary>
        [Column(IsPrimaryKey = true, Storage = "_CustomerID", Name = "CustomerID")]
        public string CustomerID
        {
            get
            {
                return this._CustomerID;
            }
            set
            {
                this._CustomerID = value;
            }

        }

        private string _City;
        [Column(Storage = "_City")]
        public string City
        {
            get
            {
                return this._City;
            }
            set
            {
                this._City = value;
            }
        }

        //------------ 定義聯繫 ------------------------
        //客戶有多個訂單，所以使用Set
        private EntitySet<Order> _Orders;
        public Customer()
        {
            this._Orders = new EntitySet<Order>();
        }

        /// <summary>
        /// 客戶導航到訂單
        /// </summary>
        /// <remarks>
        /// 使用 CustomerID 關係到 Orders OtherKey
        /// Orders 為多端，所以使用 OtherKey
        /// Order 用到的外鍵：CustomerID
        /// </remarks>
        [Association(Storage = "_Orders", OtherKey = "CustomerID")]
        public EntitySet<Order> Orders
        {
            get { return this._Orders; }
            set { this._Orders.Assign(value); }
        }
    }

注意：默认使用属性，可以使用Name指定，并且Name的值必须是数据库表存在的字段名。

方法二、使用工具，命令行/图形设计工具