Question

我有一个抽象类＆＃34; RiskBaseCollection＆＃34;使用泛型基本上是字典的容器。存储在此字典中的项目类型必须在构造函数中传递，并且它们必须从名为＆＃34; RiskBase＆＃34;的基类继承：

我在字典容器类中有一个方法，它调用数据库查询来填充字典的内容（数据库调用取决于在另一个字段中设置的内容，但这对我的观点并不重要）。

填充字典时，对于每个数据库记录，我想查看是否已经创建并存储了类的适当实例：如果有，我将检索它并向其添加其他值。如果它还没有，我创建一个RiskBase类的新实例。我已经使用Generics完成了这项工作，因此实际创建了正确类型的RiskBase。

我正在努力的是，我想告诉每个＆＃34; RiskBase＆＃34;集体拥有什么样的集合＆＃39;它。我已经尝试了各种方法，但无法让它发挥作用。

以下是Collection类的摘录，以及整个RiskBase类：

public abstract class RiskBaseCollection<T> where T : RiskBase, new() 
{
    public Dictionary<int, T> Items = new Dictionary<int, T>();

    #region Non-critical stuff
      //Removed - not important to my issue.         
    #endregion

    public void ReadData()
    {
        if (ValidConnectionInfo == false)
        {
            return;
        }

        //Create the connection:
        using (OleDbConnection conn = new OleDbConnection(ReaderConnectionString))
        {
            if (conn != null) conn.Open();
            if (conn.State == System.Data.ConnectionState.Open)
            {
                using (OleDbCommand command = new OleDbCommand(SQL, conn))
                {
                    if (command != null)
                    {
                        using (OleDbDataReader reader = command.ExecuteReader())
                        {
                            if (reader != null && reader.HasRows)
                            {
                                while (reader.Read())
                                {
                                    int RiskID = reader.GetValue<int>("ID");
                                    string Title = reader.GetValue<string>("TITLE");
                                    string Status = reader.GetValue<string>("STATUS");
                                    DateTime RaisedDate = reader.GetValue<DateTime>("RAISED_DATE");
                                    DateTime ExpiryDate = reader.GetValue<DateTime>("EXPIRY_DATE");

                                    //Get the FLOC string for the current record
                                    string FunctionalLocation = reader.GetValue<string>("FUNCTIONAL_LOCATION");

                                    T thisRisk = (Items.ContainsKey(RiskID)) ? (T)Items[RiskID] : new T();
                                    thisRisk.RiskID = RiskID;
                                    thisRisk.Title = Title;
                                    thisRisk.Status = Status;
                                    thisRisk.RaisedDate = RaisedDate;
                                    thisRisk.ExpiryDate = ExpiryDate;
                                    thisRisk.AddFunctionalLocation(FunctionalLocation);
                                    thisRisk.Owner = this;      //<=Error: Cannot implicitly convert type 'CRT.Risks.RiskBaseCollection<T>' to 'CRT.Risks.RiskBaseCollection<CRT.Risks.RiskBase>'  
                                    Items[RiskID] = thisRisk;  
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}





public class RiskBase
{
    public RiskBaseCollection<RiskBase> Owner { get; set; }
    public virtual RiskType RiskType { get; set; }

    public RiskBase() { }
    public RiskBase(RiskBaseCollection<RiskBase> riskBaseCollection, RiskType riskType)
    {
        Owner = riskBaseCollection;
        RiskType = riskType;
    }

    public virtual int RiskID { get; set; }
    public virtual string Title { get; set; }
    public virtual string Status { get; set; }
    public virtual DateTime RaisedDate { get; set; }
    public virtual DateTime ExpiryDate { get; set; }

    public virtual List<string> FunctionalLocations { get; set; } = new List<string>();
    public virtual void AddFunctionalLocation(string functionalLocation)
    {
        if (!FunctionalLocations.Contains(functionalLocation)) FunctionalLocations.Add(functionalLocation);
    }
}

基本上，我是在设置＆＃34;所有者＆＃34; RiskBase类的属性。

Answer 1

让RiskBaseCollection<T>实现covariant通用接口，并将RiskBase.Owner属性的类型更改为此接口：

// new interface
interface IRiskBaseCollection<out T>
{
    // interface members
}

public abstract class RiskBaseCollection<T> : IRiskBaseCollection<T> 
    where T : RiskBase, new() 
{
    // ...
    thisRisk.Owner = this;  // this now compiles!
}

public class RiskBase
{
    public IRiskBaseCollection<RiskBase> Owner { get; set; }    // interface reference
    // ...
}

如何告知泛型类实例有关其通用拥有集合的信息？

1 个答案: