Passing lists to the view .Net Core - asp.net

Question

Im looping through all the results from the SQL query in a .Net Core project. here is Model
public class Mymessagesinfo
{
public int MyMessagesCount { get; set; }
public List<int> MessagesIDs { get; set; }
public List<int> MessagesSendersid { get; set; }
public List<string> MessagesSenders { get; set; }
public List<string> MessagesTitles { get; set; }
public List<string> MessagesInformation { get; set; }
public List<string> MessagesStatus { get; set; }
}
I loop through the users messages in my controller then i pass that model to the view
sqlcon.Open();
int? userid = HttpContext.Session.GetInt32("UserID");
SqlCommand sqlcom = new SqlCommand("select * from messages where Messagereceiver=" +userid , sqlcon);
SqlDataReader reader = sqlcom.ExecuteReader();
if(reader.HasRows)
{
int index = 0;
while(reader.Read())
{
string s;
s = reader[0].ToString();
Mymessages.MessagesIDs.Add(int.Parse(s));
Mymessages.MessagesSendersid.Add(int.Parse(reader[1].ToString()));
Mymessages.MessagesTitles.Add(reader[3].ToString());
Mymessages.MessagesInformation.Add(reader[4].ToString());
Mymessages.MessagesStatus.Add(reader[5].ToString());
index++;
}
Mymessages.MyMessagesCount = index;
}
the very first line Mymessages.MessagesIDs.Add(int.Parse(s)); it throws an exception saying System.NullReferenceException: 'Object reference not set to an instance of an object
i wanted to make sure that reader was holding the results so i added int s and checked on it and it was holding the value it was supposed to.
whats going wrong here? is this how we are supposed to pass list-like data to the view?

Answer 1

You need to initlize MessagesIDs in entity Mymessages, like this:
var Mymessages = new Mymessagesinfo()
{
MessagesIDs = new List<int>()
};
Mymessages.MessagesIDs.Add(id);
Or just define the class like this,
public class Mymessagesinfo
{
public int MyMessagesCount { get; set; }
public List<int> MessagesIDs { get; set; } = new List<int>();
public List<int> MessagesSendersid { get; set; } = new List<int>();
public List<string> MessagesSenders { get; set; } = new List<string>();
public List<string> MessagesTitles { get; set; } = new List<string>();
public List<string> MessagesInformation { get; set; } = new List<string>();
public List<string> MessagesStatus { get; set; } = new List<string>();
}

Answer 2

Here is how I would restructure what you have to make it work.
First, your model class:
public class Mymessagesinfo
{
public List<MessageInfo> Messages { get; set; } = new List<MessageInfo>();
}
public class MessageInfo
{
public int ID { get; set; }
public int Senderid { get; set; }
public string Sender { get; set; }
public string Title { get; set; }
public string Information { get; set; }
public string Status { get; set; }
}
With this approach you have a list of message objects, instead of a bunch of lists containing property data.
Here is how I would suggest you load it from SQL Server:
var data = new Mymessagesinfo();
int? userid = HttpContext.Session.GetInt32("UserID");
var messagesTable = new System.Data.DataTable("messages");
using (var sqlcom = sqlcon.CreateCommand())
{
sqlcom.CommandText = $"select * from messages where Messagereceiver='{userid}'";
using (var adapter = new SqlDataAdapter(sqcom))
{
adapter.Fill(messagesTable);
}
}
// we are now done with SQL and have the data in memory...
foreach(DataRow row in messagesTable.Rows)
{
data.Messages.Add( new MessageInfo {
ID = row.Field<int>(0),
Senderid = row.Field<int>(1),
Sender = row.Field<string>(2),
Title = row.Field<string>(3),
Information = row.Field<string>(4),
Status = row.Field<string>(5),
});
}
return View(data);
This is a lot cleaner and by using a DataAdapter and DataTable you minimize the amount of time that the connection to the database is connected.
Here is how you would use this model in an MVC View:
#Model Mymessagesinfo
<div>
<!-- This is where you can display the properties of the message. //-->
<ul>
#foreach(var message in Model.Messages)
{
<li> #message.Title - #message.Id </li>
}
<ul>
<div>