C#中如何在在BLL的构造方法里 去构造DA

Question

public CityEntry AddCity(CityEntry city)
        {
            CityDal dal = new CityDal(); 
                return dal.AddCity(city);
        }
        public CityEntry EditCity(CityEntry city)
        {
            CityDal dal = new CityDal(); 
           return dal.EditCity(city);
        }
        public CityEntry DeleteCity(CityEntry city)
        {
            CityDal dal = new CityDal();            
                        return dal.DeleteCity(city);
        }
        public List <CityEntry> SelectCity(CityEntry city,CityIndex index)
        {
            CityDal dal = new CityDal();
            return dal.SelectCity(city,index);
        }
 可以在BLL的构造方法里 去构造DA。这样写会造成代码冗余

Answer 1

CityDal dal = new CityDal();  
public CityEntry AddCity(CityEntry city)
  {
  return dal.AddCity(city);
  }
  public CityEntry EditCity(CityEntry city)
  {
  return dal.EditCity(city);
  }
  public CityEntry DeleteCity(CityEntry city)
  {  
  return dal.DeleteCity(city);
  }
  public List <CityEntry> SelectCity(CityEntry city,CityIndex index)
  {
  return dal.SelectCity(city,index);
  }

Answer 2

你在BLL层代码中使用ADO.NET，自定义的ORM，或者EF等等，任何一个都可以轻松地操作数据库。就算是当选择数据库改变时，通过在BLL层上使用工厂方法而且换BLL，也比你这里的所谓层DA的开发工作量来的划算。十年前微软模仿java的PetShop的目的是为了对比asp.net的性能，而今天有些人把这个当作“三层”的教条，根本不能跟上形势。在.net界对（采用更加面向对象或者基于对象的）数据访问层的成熟框架早已经研究的非常透彻，远比10年前的java界要强多了。还用搞这种所谓的DA层？

Answer 3

AppConfig：
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="DAHelper_Path" value ="StyleSoft.Data.Utility"/>
    <add key="DAHelper_ClassName" value="StyleSoft.Data.DAHelper"/>
  </appSettings>
</configuration>

Answer 4

Utility：
namespace StyleSoft.BLL {
    static class Utility {
        private struct ConstProperty {
            public const string DAHelper_Path = "DAHelper_Path";
            public const string DAHelper_ClassName = "DAHelper_ClassName";
           }        private static Utility() {
            DAHelper = CreateDAHelper();
            }
        private static IDAHelper DAHelper;
        private static IDAHelper CreateDAHelper() {
            string _path = ConfigurationManager.AppSettings[ConstProperty.DAHelper_Path].ToString();
            string _className = ConfigurationManager.AppSettings[ConstProperty.DAHelper_ClassName].ToString();
            return (IDAHelper)Assembly.Load(_path).CreateInstance(_className);
            }        }    
    }//end namespace

Answer 5

应用：
public CityEntry AddCity(CityEntry city){
  return DAHelper.AddCity(city);
  }
  public CityEntry EditCity(CityEntry city){  
  return DAHelper.EditCity(city);
  }
//......

Answer 6

更正：应为：
public static