C#基础--抽象工厂

开发需求：

同一套系统，需要根据客户需求采用不同的数据库。

一般实现：

开发多套系统，每套系统对应一个数据库。

缺点：

需要同时维护多套系统，难度大。

解决：

使用抽象工厂模式，同一套系统里面开发多个数据库的DAL，根据客户需求来确定使用哪个数据库。

抽象工厂设计模式

基于抽象工厂模式设计DAL方案

项目各层之间的引用

代码示例

根据以上，建立各层，各层引用参考上面：

从底层开始构建代码：

编写不同数据库的DAL，我这里仅仅是文件夹形式将Access、SQLServer数据DAL模块分类，实际开发可以使用dll等分层。

仅做了查询Service

IDAL接口定义

DAL需要基于接口开发，所以先定义接口，我们这里仅使用到了两个接口：

using Models;

namespace IDAL
{
    public interface IClassService
    {
        List<StudentClass> GetAllClasses();
    }
}


namespace IDAL
{
    public interface IStudentService
    {
        List<Student> GetStudentsByClassId(int classId);
    }
}

基于接口开发DAL：

Access数据库

AccessHelper:

using System.Data;
using System.Data.OleDb;
using System.Configuration;

namespace DAL.Access
{
    class AccessHelper
    {
        private static readonly string connString = ConfigurationManager.ConnectionStrings["AccessConnString"].ToString();
        public static OleDbDataReader GetReader(string sql)
        {
            OleDbConnection conn = new OleDbConnection(connString);
            OleDbCommand cmd = new OleDbCommand(sql, conn);
            try
            {
                conn.Open();
                return cmd.ExecuteReader(CommandBehavior.CloseConnection);
            }
            catch (OleDbException ex)
            {
                if (conn.State == ConnectionState.Open)
                    conn.Close();
                throw new Exception("应用程序与数据库连接异常：" + ex.Message);
            }
            catch (Exception ex)
            {
                if (conn.State == ConnectionState.Open)
                    conn.Close();
                throw ex;
            }
        }
    }
}

ClassService:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using IDAL;
using Models;
using System.Data;
using System.Data.OleDb;

namespace DAL.Access
{
    class ClassService : IClassService
    {
        public List<StudentClass> GetAllClasses()
        {
            string sql = "select * from StudentClass";
            OleDbDataReader objReader = AccessHelper.GetReader(sql);
            List<StudentClass> objStuClass = new List<StudentClass>();
            while (objReader.Read())
            {
                objStuClass.Add(new StudentClass
                {
                    ClassId = Convert.ToInt32(objReader["ClassId"]),
                    ClassName = objReader["ClassName"].ToString()
                });
            }
            objReader.Close();
            return objStuClass;
        }
    }
}

StudentService:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using IDAL;
using System.Data;
using System.Data.OleDb;
using Models;

namespace DAL.Access
{
    public class StudentService : IStudentService
    {
        public List<Student> GetStudentsByClassId(int classId)
        {
            StringBuilder sqlBuilder = new StringBuilder("select StudentId,StudentName,Gender,StudentIdNo,Birthday,PhoneNumber,ClassName,Students.ClassId from Students ");
            sqlBuilder.Append("inner join StudentClass on StudentClass.ClassId=Students.ClassId ");
            if (classId > 0)
                sqlBuilder.Append($"where Students.ClassId={classId} ");
            List<Student> stuList = new List<Student>();
            OleDbDataReader objReader = null;
            try
            {
                objReader = AccessHelper.GetReader(sqlBuilder.ToString());
                while (objReader.Read())
                {
                    stuList.Add(new Student
                    {
                        StudentId = Convert.ToInt32(objReader["StudentId"]),
                        StudentName = objReader["StudentName"].ToString(),
                        Gender = objReader["Gender"].ToString(),
                        StudentIdNo = objReader["StudentIdNo"].ToString(),
                        Birthday = Convert.ToDateTime(objReader["Birthday"]),
                        PhoneNumber = objReader["PhoneNumber"].ToString(),
                        ClassName = objReader["ClassName"].ToString(),
                        ClassId = Convert.ToInt32(objReader["ClassId"])
                    });
                }
                return stuList;
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                objReader.Close();
            }
        }
    }
}

SQLServer数据库

SQLHelper:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;

namespace DAL.SQLServer
{
    class SQLHelper
    {
        private static readonly string connString=ConfigurationManager.ConnectionStrings["SqlConnString"].ToString();

        /// <summary>
        /// 增、删、改,返回受影响行数
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public static int Update(string sql)
        {
            SqlConnection conn = new SqlConnection(connString);
            SqlCommand cmd = new SqlCommand(sql, conn);
            try
            {
                conn.Open();
                return cmd.ExecuteNonQuery();
            }
            catch (SqlException ex)
            {
                if (ex.Number == 547)
                    throw new Exception("该数据已被其它表引用，不能直接删除！");
                else
                    throw new Exception("数据库操作异常：" + ex.Message);
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                conn.Close();
            }
        }
        

        /// <summary>
        /// 仅得到一条数据的查询
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public static object GetSingleResult(string sql)
        {
            SqlConnection conn = new SqlConnection(connString);
            SqlCommand cmd = new SqlCommand(sql, conn);
            try
            {
                conn.Open();
                return cmd.ExecuteScalar();
            }
            catch (SqlException ex)
            {
                throw new Exception("数据库操作异常：" + ex.Message);
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                conn.Close();
            }
        }

        /// <summary>
        /// 查询得到结果集
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public static SqlDataReader GetReader(string sql)
        {
            SqlConnection conn = new SqlConnection(connString);
            SqlCommand cmd = new SqlCommand(sql, conn);
            try
            {
                conn.Open();
                return cmd.ExecuteReader(CommandBehavior.CloseConnection);
            }
            catch (SqlException ex)
            {
                if (conn.State == ConnectionState.Open)
                    conn.Close();
                throw new Exception("应用程序与数据库连接异常：" + ex.Message);
            }
            catch (Exception ex)
            {
                if (conn.State == ConnectionState.Open)
                    conn.Close();
                throw ex;
            }
        }

        /// <summary>
        /// 查询得到数据集，前台需要多次筛选数据时使用
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public static DataSet GetDataSet(string sql)
        {
            SqlConnection conn = new SqlConnection(connString);
            SqlCommand cmd = new SqlCommand(sql, conn);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            try
            {
                conn.Open();
                da.Fill(ds);
                return ds;
            }
            catch (SqlException ex)
            {
                throw new Exception("数据库操作异常：" + ex.Message);
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                conn.Close();
            }
        }
    }
}

ClassService:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using IDAL;
using Models;
using System.Data;
using System.Data.SqlClient;

namespace DAL.SQLServer
{
    public class ClassService : IClassService
    {
        public List<StudentClass> GetAllClasses()
        {
            string sql = "select * from StudentClass";
            SqlDataReader objReader = SQLHelper.GetReader(sql);
            List<StudentClass> objStuClass = new List<StudentClass>();
            while (objReader.Read())
            {
                objStuClass.Add(new StudentClass
                {
                    ClassId = Convert.ToInt32(objReader["ClassId"]),
                    ClassName = objReader["ClassName"].ToString()
                });
            }
            objReader.Close();
            return objStuClass;
        }
    }
}

StudentService:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using IDAL;
using Models;
using System.Data;
using System.Data.SqlClient;

namespace DAL.SQLServer
{
    public class StudentService : IStudentService
    {
        public List<Student> GetStudentsByClassId(int classId)
        {
            StringBuilder sqlBuilder = new StringBuilder("select StudentId,StudentName,Gender,StudentIdNo,Birthday,PhoneNumber,ClassName,Students.ClassId from Students ");
            sqlBuilder.Append("inner join StudentClass on StudentClass.ClassId=Students.ClassId ");
            if (classId >= 0)//当==-1，说明是选的全部班级，则不需要筛选
                sqlBuilder.Append($"where Students.ClassId={classId} ");
            List<Student> stuList = new List<Student>();
            SqlDataReader objReader = null;
            try
            {
                objReader = SQLHelper.GetReader(sqlBuilder.ToString());
                while (objReader.Read())
                {
                    stuList.Add(new Student
                    {
                        StudentId = Convert.ToInt32(objReader["StudentId"]),
                        StudentName = objReader["StudentName"].ToString(),
                        Gender = objReader["Gender"].ToString(),
                        StudentIdNo = objReader["StudentIdNo"].ToString(),
                        Birthday = Convert.ToDateTime(objReader["Birthday"]),
                        PhoneNumber = objReader["PhoneNumber"].ToString(),
                        ClassName = objReader["ClassName"].ToString(),                       
                        ClassId = Convert.ToInt32(objReader["ClassId"]),                        
                    });
                }
                return stuList;
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                objReader.Close();
            }
        }
    }
}

App.Config配置

数据库用到了App.Config节点：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
  <connectionStrings>
    <add name="SqlConnString" connectionString="server=.;DataBase=StudentManageDB;Uid=sa;Pwd=warrenwell"/>
    <add name="AccessConnString" connectionString="Provider=Microsoft.ACE.OLEDB.12.0;Data Source=StudentManageDB.mdb"/>
  <!--Office版本2007以上使用以上Provider;以下：Microsoft.JET.OLEDB.4.0-->
  </connectionStrings>
  <appSettings>
    <add key="DBType" value="SQLServer"/>
    <!--<add key="DBType" value="Access"/>-->
    </appSettings>
</configuration>

Models实体类

使用到的实体类

StudentClass:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Models
{
    public class StudentClass
    {
        public int ClassId { get; set; }
        public string ClassName { get; set; }
    }
}

Students:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Models
{
    public class Student
    {
        public int StudentId { get; set; }
        public string StudentName { get; set; }
        public string Gender { get; set; }
        public DateTime Birthday { get; set; }
        public string StudentIdNo { get; set; }
        public int Age { get; set; }
        public string CardNo { get; set; }
        public string PhoneNumber { get; set; }        
        public int ClassId { get; set; }

        public string ClassName { get; set; }
    }
}

DALFactory

DALFactory根据以上App.Config里appSettings节点的key<"DBType">来选择数据库

DALAccess数据库数据访问创建类：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Configuration;
using IDAL;
using System.Reflection;

namespace DALFactory
{
    public class DataAccess
    {
        private static string dbType = "DAL."+ConfigurationManager.AppSettings["DBType"].ToString();

        public static IDAL.IClassService CreateClassService()
        {
            return (IDAL.IClassService)Assembly.Load("DAL").CreateInstance(dbType + ".ClassService");
        }

        public static IDAL.IStudentService CreateStudentService()
        {
            return (IDAL.IStudentService)Assembly.Load("DAL").CreateInstance(dbType + ".StudentService");
        }
    }
}

应用到了反射，里面Load()里面是数据库的命名空间名称，CreateInstance()里面是相应DAL的完全限定名：命名空间名称.相应Serivce名。

BLL

我们把数据访问的内容全部放到BLL里面，从而完全断绝UI与DAL的耦合。

ClassManager:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using DALFactory;
using Models;
using IDAL;

namespace BLL
{
    public class ClassManager
    {
        IDAL.IClassService objService = DALFactory.DataAccess.CreateClassService();
        public List<StudentClass> GetAllClasses()
        {
            return objService.GetAllClasses();
        }
    }
}

StudentManager:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using DALFactory;
using Models;
using IDAL;

namespace BLL
{
    public class StudentManager
    {
        IDAL.IStudentService objService = DALFactory.DataAccess.CreateStudentService();
        public List<Student> GetStudentsByClassId(int classId)
        {
            return objService.GetStudentsByClassId(classId);
        }
    }
}

UI

仅写了查询班级与学生（UI设计见下面结果展示）：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using BLL;
using Models;

namespace AbstractFactoryDemo
{
    public partial class FrmQuery : Form
    {
        public FrmQuery()
        {
            InitializeComponent();

            List<StudentClass> stuClass = new List<StudentClass>()
            {
                new StudentClass {ClassId=-1,ClassName="全部班级" }
            } ;
            stuClass.AddRange(new ClassManager().GetAllClasses());

            this.cboStudentClass.DataSource = stuClass;
            this.cboStudentClass.DisplayMember = "ClassName";
            this.cboStudentClass.ValueMember = "ClassId";

            this.dgvStudentList.AutoGenerateColumns = false;
        }

        private void btnQuery_Click(object sender, EventArgs e)
        {
            this.dgvStudentList.DataSource = new StudentManager().GetStudentsByClassId(Convert.ToInt32(this.cboStudentClass.SelectedValue));
        }
    }
}

结果展示

我们可以通过配置App.Config的相应节点来控制访问哪个数据库。

比如，我们先访问SQLServer，就这样：

访问结果：

 再去访问Access:

访问结果：

故意将两个数据库的数据格式不一致，比较容易看出来差别。

至此，抽象工厂设计模式完成。

相应源代码+数据库脚本

 https://files.cnblogs.com/files/EasonDongH/%E6%8A%BD%E8%B1%A1%E5%B7%A5%E5%8E%82%E6%BA%90%E4%BB%A3%E7%A0%81And%E6%95%B0%E6%8D%AE%E5%BA%93%E8%84%9A%E6%9C%AC.zip

注意点

有个地方需要注意，关于DAL.dll文件，如果提示不存在，则需要手动到DAL程序集下将该DAL.dll复制到项目下；如果提示“源文件与模块不一致”这样的错误，则表示你的DAL有做修改，重新生成一下DAL，再次重新将dll文件复制过去。这是经验之谈，暂未更好的解决方案，等待指教。