Possible Duplicate:
c# why cant a nullable int be assigned null as a value
如果论坛没有lastPostDate，我试图将我的reader[3]对象datetime转换为null，但它说我缺少转换.
无法确定条件表达式的类型，因为
<null>和"System.DateTime"之间没有隐式转换
public class Forums
{
public List<Forum> GetForums()
{
using (SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["CMS"].ConnectionString))
{
conn.Open();
SqlCommand cmd = new SqlCommand("sproc_Forums_GetForums", conn);
cmd.CommandType = CommandType.StoredProcedure;
SqlDataReader reader = cmd.ExecuteReader(CommandBehavior.Default);
List<Forum> forums = new List<Forum>();
while (reader.Read())
{
var title = reader[6].ToString();
var threadCount = (int)reader[5];
var lastPostTitle = reader[4].ToString();
// below is where im having a problem
Nullable<DateTime> lastPostDate = (reader[3] == DBNull.Value ? null : Convert.ToDateTime(reader[3]));
var lastPostBy = reader[2].ToString();
var forumGroup = reader[1].ToString();
var description = reader[0].ToString();
Forum forum = new Forum(0, "",DateTime.Now,
reader["Title"].ToString(),description,
0,false,"","",DateTime.Now,true,
forumGroup, (int)threadCount, lastPostBy,
lastPostDate, lastPostTitle);
forums.Add(forum);/**/
}
return forums;
}
}
}
下面是我的论坛类对象，lastPostDate为空
public class Forum
{
public Forum(int forumID, string addedBy, DateTime addedDate, string title, string description, int parentID, bool moderated,
string imageUrl, string updatedBy, DateTime? updatedDate, bool active, string forumGroup, int threadCount, string lastPostBy,
Nullable<DateTime> lastPostDate, string lastPostTitle)
{
this.ForumID = forumID;
this.AddedBy = addedBy;
this.AddedDate = addedDate;
this.Title = title;
this.Description = description;
this.ParentID = parentID;
this.Moderated = moderated;
this.ImageUrl = imageUrl;
this.UpdatedBy = updatedBy;
this.UpdatedDate = updatedDate;
this.Active = active;
this.ForumGroup = forumGroup;
this.ThreadCount = threadCount;
this.LastPostBy = lastPostBy;
this.LastPostDate = lastPostDate;
this.LastPostTitle = lastPostTitle;
}
private int _forumID;
public int ForumID
{
get { return _forumID; }
set { _forumID = value; }
}
private string _addedBy;
public string AddedBy
{
get { return _addedBy; }
set { _addedBy = value; }
}
private DateTime _addedDate = DateTime.Now;
public DateTime AddedDate
{
get { return _addedDate; }
set { _addedDate = value; }
}
private string _title = "";
public string Title
{
get { return _title; }
set { _title = value; }
}
private string _description = "";
public string Description
{
get { return _description; }
set { _description = value; }
}
private int _parentID = 0;
public int ParentID
{
get { return _parentID; }
set { _parentID = value; }
}
private bool _moderated = false;
public bool Moderated
{
get { return _moderated; }
set { _moderated = value; }
}
private string _imageUrl = "";
public string ImageUrl
{
get { return _imageUrl; }
set { _imageUrl = value; }
}
private string _updatedBy = "";
public string UpdatedBy
{
get { return _updatedBy; }
set { _updatedBy = value; }
}
private DateTime? _updatedDate = null;
public DateTime? UpdatedDate
{
get { return _updatedDate; }
set { _updatedDate = value; }
}
private bool _active = false;
public bool Active
{
get { return _active; }
set { _active = value; }
}
private string _forumGroup = "";
public string ForumGroup
{
get { return _forumGroup; }
set { _forumGroup = value; }
}
private int _threadCount = 0;
public int ThreadCount
{
get { return _threadCount; }
set { _threadCount = value; }
}
private string _lastPostBy = "";
public string LastPostBy
{
get { return _lastPostBy; }
set { _lastPostBy = value; }
}
private Nullable<DateTime> _lastPosteDate = null;
public Nullable<DateTime> LastPostDate
{
get { return _lastPosteDate; }
set { _lastPosteDate = value; }
}
private string _lastPostTitle = "";
public string LastPostTitle
{
get { return _lastPostTitle; }
set { _lastPostTitle = value; }
}
}