目前我的应用程序的UI层连接到我的DAL的DLL。达尔是这样初始化的：

 为AS400 //初始化数据访问
达尔= JDE8Dal.Instance;
Dal.conString = Properties.Settings.Default.conAS400;
 

DAL是desinged为单例。我认为，迫使应用程序有一个实例是一个好主意。

DAL：

 公共类JDE8Dal
    {
        公共字符串conString {获得;组; }
        私人静态只读JDE8Dal _instance =新JDE8Dal（）;
        私人JDE8Dal（）
        {
        }
        公共静态JDE8Dal实例
        {
            {返回_instance; }
        }
        //方法
    }
 

我的BLL会是这个样子：

 命名空间YLA.Bar code
{
    公共静态类YlaBar codeUtil
    {
        公共静态字符串LotStripZeroes（字符串str）
        {
            VAR RET =海峡;
            如果（str.Trim（）。StartsWith（00））
            {
                RET = YlaGeneralUtilities.StripLeadingNumofChars（STR，2）;
            }
            返回RET;
        }
    }

公共类酒吧codeBLL
{
    // DAL INIT在这里？
}
}
 

现在，我需要建立更多的应用程序，我需要进入一个3层架构，并开始阅读DDD。

1）如何移动DAL处理中BLL？只需添加初始化我BLL节？

2）我应该让我的DAL设计为单身或没有？

您应该使用反向控制模式，以降低层间的依赖关系。你的情况我会用一个构造函数注入的数据上下文所要求的类：

  public类吧codeBLL
{
    私人JDE8Dal _context;

    公共酒吧codeBLL（JDE8Dal上下文）
    {
        _context =背景;
    }
}
 

数据方面应该是短暂的对象。如果您正在开发一个Web应用程序，你应该实例每个请求一个数据上下文。我也建议使用ORM（实体框架/ NHibernate的）。

Currently my application's UI layer is coupled to my DAL dll. Dal is initialized like this:

//Initialize Data Access for AS400
Dal = JDE8Dal.Instance;
Dal.conString = Properties.Settings.Default.conAS400;

DAL is desinged as singleton. I thought that forcing the application to have one instance is a good idea.

DAL:

public class JDE8Dal
    {
        public string conString { get; set; }
        private static readonly JDE8Dal _instance = new JDE8Dal();
        private JDE8Dal()
        {
        }
        public static JDE8Dal Instance
        {
            get { return _instance; }
        }
        // Methods
    }

My BLL will look something like this:

namespace YLA.Barcode
{
    public static class YlaBarcodeUtil
    {
        public static string LotStripZeroes(string str)
        {
            var ret = str;
            if (str.Trim().StartsWith("00"))
            {
                ret = YlaGeneralUtilities.StripLeadingNumofChars(str, 2);
            }
            return ret;
        }
    }

public class BarcodeBLL
{
    //DAL INIT HERE?
}
}

Now that i need to build more applications i need to move into a 3 layer architecture and start reading on DDD.

1) How to move the DAL handling in BLL? Just add the initialization in my BLL section?

2) Should i keep my DAL design as singleton or not?

You should use the Inversion of Control pattern to reduce the dependency between your layers. In your case I would use a constructor injection as the data context is required by your class:

public class BarcodeBLL
{
    private JDE8Dal _context;

    public BarcodeBLL(JDE8Dal context)
    {
        _context = context;
    }
}

Data context should be short lived objects. If you're developing a web application you should instantiate one data context per request. I would also recommend using an ORM (Entity Framework / NHibernate).