基于LINQ to SQL的WEB三层架构（上）

　　LINQ语言集成查询是微软用于抗衡竞争对手，改进现有开发模式下面向数据库操作问题的一个种全新体系架构。它的出现，解决了面向对象开发中由数据库操作引起的先天性的瓶颈，使得面向对象和数据库完美结合，程序员不再受限于复杂的SQL脚本，而可以一种近乎完美的方式来搭建自己的面向对象型软件系统，这种方式就是将数据完全对象化，将SQL语句封装到底层，由framework来完成，程序员只需面向数据库对象来编程，从另一种意义上来说，是把数据也程序化了。

　　LINQ的这种开发模式也改变了系统架构的搭建方式，在以往的系统中，数据访问层DAL要访问数据字段，业务逻辑层BLL要得到数据都需要通过数据模型层Model来处理，而LINQ和VS2008为我们带来了一种全新的自动化方式生成数据模型层，这就是dbml（Database Mark Language。数据库描述语言，是一种xml格式的文档，用来描述数据库），有了它我们就不需要去找那些第三方的代码生成工具，只需要把数据表拖拽到设计器中，如下图所示，DONET便为我们做好了一切。

      完成拖拽操作后，VS会自动生成一个数据模型层的dbml文件和相关的类文件。这样我们省去了数据模型层的搭建，系统的架构也就有所不同，以下用一个例子简单的讲一下该架构模型。

      为了完成这个架构，我们首先要创建一个WEB APPLICATION项目，在新建项目窗口选择“ASP.NET WEB应用程序”，为它取一个名字，并确定。

 

      接下来，在解决方案资源管理器中再添加一个类库项目，取名为DAL，如下图：

      再使用同样的方法在解决方案资源管理器中添加一个类库项目，取名为BLL，这样我们的基础架构搭建完成，此时我们的解决方案资源管理器应该是如下结构。

      此时，我们先从DAL项目入手，在DAL项目中，添加一个LINQ TO SQL类，取名为Northwind（为了方便起见，此项目使用SQL SERVER2005中的Northwind示例数据库），双击新建立的Northwind.dbml文件，然后打开“服务器资源管理器”，建立与数据的连接，并从Northwind数据库中，将Employees表拖拽到Northwind.dbml文件的可视化设计器中。

 

      初始的Northwind.dbml文件代码如下：

#pragma warning disable 1591
//------------------------------------------------------------------------------
// <auto-generated>
//     此代码由工具生成。
//     运行时版本:2.0.50727.3053
//
//     对此文件的更改可能会导致不正确的行为，并且如果
//     重新生成代码，这些更改将会丢失。
// </auto-generated>
//------------------------------------------------------------------------------

namespace DAL
{
    using System.Data.Linq;
    using System.Data.Linq.Mapping;
    using System.Data;
    using System.Collections.Generic;
    using System.Reflection;
    using System.Linq;
    using System.Linq.Expressions;
    using System.ComponentModel;
    using System;
    
    
    [System.Data.Linq.Mapping.DatabaseAttribute(Name="Northwind")]
    public partial class NorthwindDataContext : System.Data.Linq.DataContext
    {
        
        private static System.Data.Linq.Mapping.MappingSource mappingSource = new AttributeMappingSource();
        
    #region Extensibility Method Definitions
    partial void OnCreated();
    partial void InsertEmployees(Employees instance);
    partial void UpdateEmployees(Employees instance);
    partial void DeleteEmployees(Employees instance);
    #endregion
        
        public NorthwindDataContext() : 
                base(global::DAL.Properties.Settings.Default.NorthwindConnectionString, mappingSource)
        {
            OnCreated();
        }
        
        public NorthwindDataContext(string connection) : 
                base(connection, mappingSource)
        {
            OnCreated();
        }
        
        public NorthwindDataContext(System.Data.IDbConnection connection) : 
                base(connection, mappingSource)
        {
            OnCreated();
        }
        
        public NorthwindDataContext(string connection, System.Data.Linq.Mapping.MappingSource mappingSource) : 
                base(connection, mappingSource)
        {
            OnCreated();
        }
        
        public NorthwindDataContext(System.Data.IDbConnection connection, System.Data.Linq.Mapping.MappingSource mappingSource) : 
                base(connection, mappingSource)
        {
            OnCreated();
        }
        
        public System.Data.Linq.Table<Employees> Employees
        {
            get
            {
                return this.GetTable<Employees>();
            }
        }
    }
    
    [Table(Name="dbo.Employees")]
    public partial class Employees : INotifyPropertyChanging, INotifyPropertyChanged
    {
        
        private static PropertyChangingEventArgs emptyChangingEventArgs = new PropertyChangingEventArgs(String.Empty);
        
        private int _EmployeeID;
        
        private string _LastName;
        
        private string _FirstName;
        
        private string _Title;
        
        private string _TitleOfCourtesy;
        
        private System.Nullable<System.DateTime> _BirthDate;
        
        private System.Nullable<System.DateTime> _HireDate;
        
        private string _Address;
        
        private string _City;
        
        private string _Region;
        
        private string _PostalCode;
        
        private string _Country;
        
        private string _HomePhone;
        
        private string _Extension;
        
        private System.Data.Linq.Binary _Photo;
        
        private string _Notes;
        
        private System.Nullable<int> _ReportsTo;
        
        private string _PhotoPath;
        
    #region Extensibility Method Definitions
    partial void OnLoaded();
    partial void OnValidate(System.Data.Linq.ChangeAction action);
    partial void OnCreated();
    partial void OnEmployeeIDChanging(int value);
    partial void OnEmployeeIDChanged();
    partial void OnLastNameChanging(string value);
    partial void OnLastNameChanged();
    partial void OnFirstNameChanging(string value);
    partial void OnFirstNameChanged();
    partial void OnTitleChanging(string value);
    partial void OnTitleChanged();
    partial void OnTitleOfCourtesyChanging(string value);
    partial void OnTitleOfCourtesyChanged();
    partial void OnBirthDateChanging(System.Nullable<System.DateTime> value);
    partial void OnBirthDateChanged();
    partial void OnHireDateChanging(System.Nullable<System.DateTime> value);
    partial void OnHireDateChanged();
    partial void OnAddressChanging(string value);
    partial void OnAddressChanged();
    partial void OnCityChanging(string value);
    partial void OnCityChanged();
    partial void OnRegionChanging(string value);
    partial void OnRegionChanged();
    partial void OnPostalCodeChanging(string value);
    partial void OnPostalCodeChanged();
    partial void OnCountryChanging(string value);
    partial void OnCountryChanged();
    partial void OnHomePhoneChanging(string value);
    partial void OnHomePhoneChanged();
    partial void OnExtensionChanging(string value);
    partial void OnExtensionChanged();
    partial void OnPhotoChanging(System.Data.Linq.Binary value);
    partial void OnPhotoChanged();
    partial void OnNotesChanging(string value);
    partial void OnNotesChanged();
    partial void OnReportsToChanging(System.Nullable<int> value);
    partial void OnReportsToChanged();
    partial void OnPhotoPathChanging(string value);
    partial void OnPhotoPathChanged();
    #endregion
        
        public Employees()
        {
            OnCreated();
        }
        
        [Column(Storage="_EmployeeID", DbType="Int NOT NULL", IsPrimaryKey=true)]
        public int EmployeeID
        {
            get
            {
                return this._EmployeeID;
            }
            set
            {
                if ((this._EmployeeID != value))
                {
                    this.OnEmployeeIDChanging(value);
                    this.SendPropertyChanging();
                    this._EmployeeID = value;
                    this.SendPropertyChanged("EmployeeID");
                    this.OnEmployeeIDChanged();
                }
            }
        }
        
        [Column(Storage="_LastName", DbType="NVarChar(20) NOT NULL", CanBeNull=false)]
        public string LastName
        {
            get
            {
                return this._LastName;
            }
            set
            {
                if ((this._LastName != value))
                {
                    this.OnLastNameChanging(value);
                    this.SendPropertyChanging();
                    this._LastName = value;
                    this.SendPropertyChanged("LastName");
                    this.OnLastNameChanged();
                }
            }
        }
        
        [Column(Storage="_FirstName", DbType="NVarChar(10) NOT NULL", CanBeNull=false)]
        public string FirstName
        {
            get
            {
                return this._FirstName;
            }
            set
            {
                if ((this._FirstName != value))
                {
                    this.OnFirstNameChanging(value);
                    this.SendPropertyChanging();
                    this._FirstName = value;
                    this.SendPropertyChanged("FirstName");
                    this.OnFirstNameChanged();
                }
            }
        }
        
        [Column(Storage="_Title", DbType="NVarChar(30)")]
        public string Title
        {
            get
            {
                return this._Title;
            }
            set
            {
                if ((this._Title != value))
                {
                    this.OnTitleChanging(value);
                    this.SendPropertyChanging();
                    this._Title = value;
                    this.SendPropertyChanged("Title");
                    this.OnTitleChanged();
                }
            }
        }
        
        [Column(Storage="_TitleOfCourtesy", DbType="NVarChar(25)")]
        public string TitleOfCourtesy
        {
            get
            {
                return this._TitleOfCourtesy;
            }
            set
            {
                if ((this._TitleOfCourtesy != value))
                {
                    this.OnTitleOfCourtesyChanging(value);
                    this.SendPropertyChanging();
                    this._TitleOfCourtesy = value;
                    this.SendPropertyChanged("TitleOfCourtesy");
                    this.OnTitleOfCourtesyChanged();
                }
            }
        }
        
        [Column(Storage="_BirthDate", DbType="DateTime")]
        public System.Nullable<System.DateTime> BirthDate
        {
            get
            {
                return this._BirthDate;
            }
            set
            {
                if ((this._BirthDate != value))
                {
                    this.OnBirthDateChanging(value);
                    this.SendPropertyChanging();
                    this._BirthDate = value;
                    this.SendPropertyChanged("BirthDate");
                    this.OnBirthDateChanged();
                }
            }
        }
        
        [Column(Storage="_HireDate", DbType="DateTime")]
        public System.Nullable<System.DateTime> HireDate
        {
            get
            {
                return this._HireDate;
            }
            set
            {
                if ((this._HireDate != value))
                {
                    this.OnHireDateChanging(value);
                    this.SendPropertyChanging();
                    this._HireDate = value;
                    this.SendPropertyChanged("HireDate");
                    this.OnHireDateChanged();
                }
            }
        }
        
        [Column(Storage="_Address", DbType="NVarChar(60)")]
        public string Address
        {
            get
            {
                return this._Address;
            }
            set
            {
                if ((this._Address != value))
                {
                    this.OnAddressChanging(value);
                    this.SendPropertyChanging();
                    this._Address = value;
                    this.SendPropertyChanged("Address");
                    this.OnAddressChanged();
                }
            }
        }
        
        [Column(Storage="_City", DbType="NVarChar(15)")]
        public string City
        {
            get
            {
                return this._City;
            }
            set
            {
                if ((this._City != value))
                {
                    this.OnCityChanging(value);
                    this.SendPropertyChanging();
                    this._City = value;
                    this.SendPropertyChanged("City");
                    this.OnCityChanged();
                }
            }
        }
        
        [Column(Storage="_Region", DbType="NVarChar(15)")]
        public string Region
        {
            get
            {
                return this._Region;
            }
            set
            {
                if ((this._Region != value))
                {
                    this.OnRegionChanging(value);
                    this.SendPropertyChanging();
                    this._Region = value;
                    this.SendPropertyChanged("Region");
                    this.OnRegionChanged();
                }
            }
        }
        
        [Column(Storage="_PostalCode", DbType="NVarChar(10)")]
        public string PostalCode
        {
            get
            {
                return this._PostalCode;
            }
            set
            {
                if ((this._PostalCode != value))
                {
                    this.OnPostalCodeChanging(value);
                    this.SendPropertyChanging();
                    this._PostalCode = value;
                    this.SendPropertyChanged("PostalCode");
                    this.OnPostalCodeChanged();
                }
            }
        }
        
        [Column(Storage="_Country", DbType="NVarChar(15)")]
        public string Country
        {
            get
            {
                return this._Country;
            }
            set
            {
                if ((this._Country != value))
                {
                    this.OnCountryChanging(value);
                    this.SendPropertyChanging();
                    this._Country = value;
                    this.SendPropertyChanged("Country");
                    this.OnCountryChanged();
                }
            }
        }
        
        [Column(Storage="_HomePhone", DbType="NVarChar(24)")]
        public string HomePhone
        {
            get
            {
                return this._HomePhone;
            }
            set
            {
                if ((this._HomePhone != value))
                {
                    this.OnHomePhoneChanging(value);
                    this.SendPropertyChanging();
                    this._HomePhone = value;
                    this.SendPropertyChanged("HomePhone");
                    this.OnHomePhoneChanged();
                }
            }
        }
        
        [Column(Storage="_Extension", DbType="NVarChar(4)")]
        public string Extension
        {
            get
            {
                return this._Extension;
            }
            set
            {
                if ((this._Extension != value))
                {
                    this.OnExtensionChanging(value);
                    this.SendPropertyChanging();
                    this._Extension = value;
                    this.SendPropertyChanged("Extension");
                    this.OnExtensionChanged();
                }
            }
        }
        
        [Column(Storage="_Photo", DbType="Image", UpdateCheck=UpdateCheck.Never)]
        public System.Data.Linq.Binary Photo
        {
            get
            {
                return this._Photo;
            }
            set
            {
                if ((this._Photo != value))
                {
                    this.OnPhotoChanging(value);
                    this.SendPropertyChanging();
                    this._Photo = value;
                    this.SendPropertyChanged("Photo");
                    this.OnPhotoChanged();
                }
            }
        }
        
        [Column(Storage="_Notes", DbType="NText", UpdateCheck=UpdateCheck.Never)]
        public string Notes
        {
            get
            {
                return this._Notes;
            }
            set
            {
                if ((this._Notes != value))
                {
                    this.OnNotesChanging(value);
                    this.SendPropertyChanging();
                    this._Notes = value;
                    this.SendPropertyChanged("Notes");
                    this.OnNotesChanged();
                }
            }
        }
        
        [Column(Storage="_ReportsTo", DbType="Int")]
        public System.Nullable<int> ReportsTo
        {
            get
            {
                return this._ReportsTo;
            }
            set
            {
                if ((this._ReportsTo != value))
                {
                    this.OnReportsToChanging(value);
                    this.SendPropertyChanging();
                    this._ReportsTo = value;
                    this.SendPropertyChanged("ReportsTo");
                    this.OnReportsToChanged();
                }
            }
        }
        
        [Column(Storage="_PhotoPath", DbType="NVarChar(255)")]
        public string PhotoPath
        {
            get
            {
                return this._PhotoPath;
            }
            set
            {
                if ((this._PhotoPath != value))
                {
                    this.OnPhotoPathChanging(value);
                    this.SendPropertyChanging();
                    this._PhotoPath = value;
                    this.SendPropertyChanged("PhotoPath");
                    this.OnPhotoPathChanged();
                }
            }
        }
        
        public event PropertyChangingEventHandler PropertyChanging;
        
        public event PropertyChangedEventHandler PropertyChanged;
        
        protected virtual void SendPropertyChanging()
        {
            if ((this.PropertyChanging != null))
            {
                this.PropertyChanging(this, emptyChangingEventArgs);
            }
        }
        
        protected virtual void SendPropertyChanged(String propertyName)
        {
            if ((this.PropertyChanged != null))
            {
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}
#pragma warning restore 1591

  

      从中可以看到，这里本质上就是以前的数据模型层，将数据整个对象化了，为了层之间的访问方便，我们将改类的命名空间改为Auto.DAL，并将NorthwindDataContent类的第一个构造函数代码修改如下，这样修改主要是为了统一数据库连接字符串的位置，因为dbml文件在生成后会附带生成一个app.config文件，用来存放连接字符串，而我们要把连接字符串统一放到web.config中。（要访问web.config文件，需要为DAL项目添加对System.Configuration的应用）

public NorthwindDataContext() :
        base(ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString, mappingSource)
        {
            OnCreated();
        }

     

基于LINQ to SQL的WEB三层架构（下）