C# 如何在不从我的对象调用我的业务对象层的情况下延迟加载

简单问题 我有一个阶级发言人，他拥有另一个阶级发言人部门的成员作为财产。 就守则而言：

class person {
public string fname {get; set;}
public string lname {get; set;}
public Department d {get; set;}
}

当我加载一个人时，我让我的前端网站调用我的业务对象层，然后调用我的数据访问层，大意如下：

website:
Person p;
p = BOL.GetPerson(1); //call function that returns a person

在我的业务对象层中，我只需执行一些业务逻辑并调用数据访问层，如下所示：

BOL：

在我的DAL中，我只是调用一个存储过程，从一个人的表中提取这些信息。唯一的问题是我不拉部门数据，因为它是一个相当大的结构

因此，我的问题是，在对象不知道或调用业务对象层的情况下，如何在get属性中延迟加载这个department对象。此外，我认为将

Department

对象与

BOL

对象紧密耦合是不好的做法

换句话说，我不想在我的个人课上这样做：

public Department d {
  get 
     {
      if(d==null)
           {
            d = BOL.GetDepartmentInfo();
           }
     }
  set 
       {
        //some code
        }

这是一个

person

类，它应该只包含关于一个人的相关信息，所以它实际上不应该知道业务对象层

我怎样才能解决这个问题

编辑 这里是酒店：

public FunctionalGroup Department
{
    get
    {
        if (Department == null)
        {
            Department = GetDepartment();
        }
    }
    set
    {
        Department = value;
    }
}

public Action<FunctionalGroup> GetDepartment { private get; set; }

第二次编辑 基本上这就是我所拥有的：

 private FunctionalGroup _d = null;

        public FunctionalGroup Department
        {
            get
            {
                if (_d == null)
                {
                    _d = GetDepartment();
                }
                return _d;
            }
            set
            {
                _d = value;
            }
        }

//        public Action<string, FunctionalGroup> GetDepartment { private get; set; }

        public Func<FunctionalGroup> GetDepartment { private get; set; }

我的DAL看起来像这样：

  /// <summary>
        /// Returns a functional group object along with all of its properties, otherwise null.
        /// </summary>
        /// <param name="fgID">String representation of a functional group (ex: "A-AD-C")</param>
        /// <returns>Functional group object with all associated properties, otherwise null.</returns>
        public static FunctionalGroup GetFunctionalGroup(string fgID)
        {
            FunctionalGroup fg = null;

            if (fgID.Length != 0)
            {
                  //connString = the string of our database app found in the resource file
                using (SqlConnection con = new SqlConnection(connString))
                {
                    using (SqlCommand cmd = new SqlCommand("EMPDLL_selFunctionalGroupByFunctionalGroupID", con))
                    {
                        cmd.CommandType = CommandType.StoredProcedure;
                        cmd.Parameters.Add("@FunctionalGroupID", SqlDbType.VarChar).Value = fgID;
                        con.Open();

                        using (SqlDataReader reader = cmd.ExecuteReader())
                        {
                            if (reader.HasRows)
                            {
                                if (reader.Read())
                                {
                                    //found a func group
                                    fg = new FunctionalGroup((string)reader["FunctionalGroupID"],
                                                             (long)reader["ClientID"],
                                                             (string)reader["CostCenter"],
                                                             (string)reader["Description"],
                                                             (string)reader["Comments"],
                                                             (string)reader["AddedBy"],
                                                              reader["DateAdded"] == DBNull.Value ? null : (DateTime?)reader["DateAdded"],
                                                             (string)reader["ModifiedBy"],
                                                             reader["DateModified"] == DBNull.Value ? null : (DateTime?)reader["DateModified"],
                                                             (bool)reader["Inactive"]);
                                }
                            }
                        }
                    }
                }
            }
            return fg;
        }

---

您可以为person对象提供一个回调方法，该方法可以为此人加载部门：

class person {

  private Department _department = null;

  public Func<Department> GetDepartment { private get; set; }

  public string fname { get; set; }
  public string lname { get; set; }

  public Department d {
    get {
      if (_department == null) {
        _department = GetDepartment();
      }
      return _department;
    }
  }

}

---

也可以利用

Lazy

类型来处理延迟初始化。可以很好地与委托一起工作。@Guffa-我想我不明白这一点……让我们假设我创建了一个person对象，而现在department对象为空。在你说的属性中，

\u department=GetDepartment（）在哪里定义GetDepartment？如果你说在person类中，那么这并不能解决问题，因为这个方法将不得不调用业务对象层…好的，在重新阅读它之后，它是有意义的，我看到它变成了一种委托类型，并在需要时调用BOL。非常好的解决方案+1。@Guffa-一个问题是，是否可以将参数传递给
GetDepartment
？下面是我尝试的代码：
e.GetDepartment=（）=>BOL.GetFunctionalGroup（（string）reader[“FunctionalGroupID]”）错误为错误1代表“System.Action”不需要0个参数我意识到我的错误，guffa获得了积分：代码根据上述编辑进行了更改。
public static FunctionalGroup GetFunctionalGroup(string fgID)
 {
  return DAL.GetFunctionalGroup(fgID);
 }

  /// <summary>
        /// Returns a functional group object along with all of its properties, otherwise null.
        /// </summary>
        /// <param name="fgID">String representation of a functional group (ex: "A-AD-C")</param>
        /// <returns>Functional group object with all associated properties, otherwise null.</returns>
        public static FunctionalGroup GetFunctionalGroup(string fgID)
        {
            FunctionalGroup fg = null;

            if (fgID.Length != 0)
            {
                  //connString = the string of our database app found in the resource file
                using (SqlConnection con = new SqlConnection(connString))
                {
                    using (SqlCommand cmd = new SqlCommand("EMPDLL_selFunctionalGroupByFunctionalGroupID", con))
                    {
                        cmd.CommandType = CommandType.StoredProcedure;
                        cmd.Parameters.Add("@FunctionalGroupID", SqlDbType.VarChar).Value = fgID;
                        con.Open();

                        using (SqlDataReader reader = cmd.ExecuteReader())
                        {
                            if (reader.HasRows)
                            {
                                if (reader.Read())
                                {
                                    //found a func group
                                    fg = new FunctionalGroup((string)reader["FunctionalGroupID"],
                                                             (long)reader["ClientID"],
                                                             (string)reader["CostCenter"],
                                                             (string)reader["Description"],
                                                             (string)reader["Comments"],
                                                             (string)reader["AddedBy"],
                                                              reader["DateAdded"] == DBNull.Value ? null : (DateTime?)reader["DateAdded"],
                                                             (string)reader["ModifiedBy"],
                                                             reader["DateModified"] == DBNull.Value ? null : (DateTime?)reader["DateModified"],
                                                             (bool)reader["Inactive"]);
                                }
                            }
                        }
                    }
                }
            }
            return fg;
        }

 private FunctionalGroup _d = null;

        public FunctionalGroup Department
        {
            get
            {
                if (_d == null)
                {
                    _d = GetDepartment();
                }
                return _d;
            }
            set
            {
                _d = value;
            }
        }

        public Func<FunctionalGroup> GetDepartment { private get; set; }

class person {

  private Department _department = null;

  public Func<Department> GetDepartment { private get; set; }

  public string fname { get; set; }
  public string lname { get; set; }

  public Department d {
    get {
      if (_department == null) {
        _department = GetDepartment();
      }
      return _department;
    }
  }

}

p.GetDepartment = () => BOL.GetDepartment(1);