This is the code i am using to select Maximum RollNo based on Class field value.
But when there is no data about Class Field in Table. Then Error is generated.
using (var conn = new OleDbConnection(DatabaseObjects.ConnectionString))
{
conn.Open();
command = new OleDbCommand("select max(RollNo) as Roll from Students where Class = '"+cmbClass.Text+"'", conn);
OleDbDataReader dr = command.ExecuteReader();
if (!dr.IsDBNull(0))
{
while (dr.Read())
{
i = Convert.ToInt32(dr["Roll"]);
}
}
InvalidOperation Exception is occurring. I want to get value of RollNo if data is available in Table. If data is not available in Table then what should I do?
you are inversing the steps :
open the connection;
check is there is comming data;
check if the value is not null;
read the data;
try this :
while (dr.Read())
{
if (!dr.IsDBNull(0))
{
i = Convert.ToInt32(dr["Roll"]);
}
}
while your are attending just single value, use executeScalar to get the value ;
conn.Open();
command = new OleDbCommand("select isnull(max(RollNo),-1) as Roll from Students where Class = '"+cmbClass.Text+"'", conn);
int rollNo = (int) command.ExecuteScallar();
if(rollno !=-1)
{
// TODO :
}
Related
First post here. I'm trying to create a website that fetches data from an Oracle database and returns some tables. I was able to connect my database fine and made a DataConnector that returns a list of CodeDesc objects. My main problem right now is simply displaying that data to the screen, preferably in the form of a drop down list but I'm using a GridView for now.
Here's my front end:
protected void Button1_Click(object sender, EventArgs e)
{
DataConnector dc = new DataConnector();
GridView2.DataSource = dc.getCodeTypes();
GridView2.DataBind();
}
When I click the button, nothing is generated and the debugger only says "Exception thrown: 'System.ArgumentException' in Oracle.DataAccess.dll" Any help would be appreciated. This is my first time doing web development and it's been a struggle to get even this far. I'm using Visual Studio 2015
Back End:
//Create datatable to get info from db & return results
public List<CodeDesc> getCodeTypes()
{
try
{
OracleConnection con = new OracleConnection(connString);
con.Open();
string query = "select id, descr from code_desc where code_type_id = 0";
// Create the OracleCommand
OracleCommand cmd = new OracleCommand();
cmd.Connection = con;
cmd.CommandType = CommandType.Text;
// Execute command, create OracleDataReader object
OracleDataReader reader = cmd.ExecuteReader();
List<CodeDesc> L = new List<CodeDesc>();
while (reader.Read())
{
CodeDesc c = new CodeDesc();
c.id = reader.GetInt32(0);
c.description = reader.GetString(1);
L.Add(c);
}
// Clean up
reader.Dispose();
cmd.Dispose();
con.Dispose();
System.Diagnostics.Debug.WriteLine(L);
return L;
}
catch (Exception ex)
{
// catch clause here...
}
}
CodeDesc:
public class CodeDesc
{
public int id { get; set; }
public string description { get; set; }
}
Any help would be great.
You never set the query string to the CommandText property of the OracleCommand. Of course this can only result in an exception when you try to execute your command.
Said that, remember that every disposable object should be enclosed in a using statement. This is very important in case of exceptions because the correct closing and disposing is executed automatically exiting from the using block
public List<CodeDesc> getCodeTypes()
{
try
{
List<CodeDesc> L = new List<CodeDesc>();
string query = "select id, descr from code_desc where code_type_id = 0";
using(OracleConnection con = new OracleConnection(connString))
using(OracleCommand cmd = new OracleCommand(query, con))
{
con.Open();
// Execute command, create OracleDataReader object
using(OracleDataReader reader = cmd.ExecuteReader())
{
while (reader.Read())
{
CodeDesc c = new CodeDesc();
c.id = reader.GetInt32(0);
c.description = reader.GetString(1);
L.Add(c);
}
}
}
System.Diagnostics.Debug.WriteLine(L);
return L;
}
I was trying to add a combo box which could get all the product name but unfortunately I follow some tutorials and end up like this.
void fillCombo()
{
try
{
con.Open();
OleDbCommand command = new OleDbCommand("Select * from IblInventory");
command.Connection = con;
OleDbDataReader reader = command.ExecuteReader();
while (reader.Read())
{
String product = reader.GetString("ProductName"); // << invalid argument
cmbProduct.Items.Add(product);
}
con.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
What could possibly the reason?
From the documentation of OleDbDataReader.GetString you will notice that the argument required by the method is an integer representing the position of the column in the returned record not its name.
If you (rightly) prefer to use the column name then you need to take a detour and use the GetOrdinal method to retrieve the position of the column given the name.
while (reader.Read())
{
int pos = reader.GetOrdinal("ProductName");
String product = reader.GetString(pos);
cmbProduct.Items.Add(product);
}
Another example, practically identical to your situation, can be found in the documentation page on MSDN about OleDbDataReader.GetOrdinal
It is also a common practice to write an extension method that allows you to write code as yours hiding the details of the mapping between name and position. You just need a static class with
public static class ReaderExtensions
{
public string GetString(this OleDbDataReader reader, string colName)
{
string result = "";
if(!string.IsNullOrEmpty(colName))
{
int pos = reader.GetOrdinal(colName);
result = reader.GetString(pos);
}
return result;
}
... other extensions for Int, Decimals, DateTime etc...
}
Now with this class in place and accessible you can call
string product = reader.GetString("ProductName");
it is working in my project
First fill your data in to datatable see the below code
DataTable results = new DataTable();
using(OleDbConnection conn = new OleDbConnection(connString))
{
OleDbCommand cmd = new OleDbCommand("Select * from IblInventory", conn);
conn.Open();
OleDbDataAdapter adapter = new OleDbDataAdapter(cmd);
adapter.Fill(results);
}
Now
cmbProduct.DataSource = results ;
cmbProduct.DisplayMember = "ProductName";
cmbProduct.ValueMember = "Id feild of IblInventory table";
I have little problem I am trying to add sequenced numbers in front the data that I will retrieve from a SQL Server database as shown below.
public partial class Form1 : Form
{
SqlConnection con = new SqlConnection(#"Server=.;database=test;integrated security=false;user id=sa;pwd=#admin00");
SqlCommand com = new SqlCommand();
SqlDataReader dr;
public Form1()
{
InitializeComponent();
com.CommandText = "select book_name from Table_book";
com.Connection = con;
con.Open();
dr = com.ExecuteReader();
while (dr.Read())
{
for (int i = 1; i <= dr.FieldCount; i++)
{
listBox1.Items.Add(i+"-"+dr[0].ToString());
i += i;
}
}
if (listBox1.Items.Count == 0)
{
MessageBox.Show("No Data Found");
}
dr.Close();
con.Close();
}
And the result will be like that:
TY all
I just use my server Id sequence to solve the problem like that:
SqlConnection con = new SqlConnection(#"server=.;database=test;integrated security=false;user id=sa;pwd=#admin00");
con.Open();
SqlCommand sqlcom = new SqlCommand("select book_id,book_name from Table_book", con);
SqlDataReader sqlDR=sqlcom.ExecuteReader();
while(sqlDR.Read())
{
listBox1.Items.Add(sqlDR["book_id"].ToString()+"-"+sqlDR["book_name"].ToString());
}
Add is capable of operating on objects, not just on strings.
Why?
class ModelClass {
// for use in algorithm, may be presented in GUI or not
int Sequence { get; set; }
string Description { get ; set ;}
// ... what You want, is is typical model class
override string ToString() {
// return what you want, is presented in GUI
return Descrition;
}
ModelClass( string n, int i ) ...
}
...
listBox.Items.Add( new ModelClass(i.ToString(), dr[...] // sequence )
Now you can check whatever you want from Items, because these are objects of ModelClass.
Code written by hand, non tested in IDE.
You're setting the "sequence number" to the number of fields returned in the results while iterating over each row with the dr.Read().
It's unnecessary for the for loop. What you should be doing is setting your counter variable outside of the dr.Read() and then incrementing it inside...
int i = 1;
while (dr.Read())
{
// set listbox item text
listBox1.Items.Add(i.ToString() + "-" + dr[0].ToString());
i+=1;
}
i have a php code.here is the code,i gonna to translate it to .NET but in some point i'm getting some trouble.
function processInput($conn, $MessageArray, $mobilenumber, $date, $odd)
{
$strSQLUSER="SELECT * FROM tbl_tiduser WHERE username='".addslashes($MessageArray[0])."' AND stat!='1' AND stat!='4'";
$result_user=odbc_exec($conn,$strSQLUSER) or die("Could not connect to database");
here is the converted .NET code
public class ProcessInput
{
private string msg_arr;
private string MooseSeenInput(string MobileNo,string Date,string odd,params Array[] msg_arr)
{
SqlCommand com = new SqlCommand("SELECT * FROM tbl_tiduser WHERE username=#username AND stat!='1' AND stat!='4'", mycon);
com.Parameters.AddWithValue("#username",username);
using (SqlDataReader reader = com.ExecuteReader())
// whats the next part need to come here ???
}
this is incomplete.i'm not going to compile it....
private static void ReadOrderData(string connectionString)
{
string queryString =
"SELECT OrderID, CustomerID FROM dbo.Orders;";
using (SqlConnection connection =
new SqlConnection(connectionString))
{
SqlCommand command =
new SqlCommand(queryString, connection);
connection.Open();
SqlDataReader reader = command.ExecuteReader();
// Call Read before accessing data.
while (reader.Read())
{
Console.WriteLine(String.Format("{0}, {1}",
reader[0], reader[1]));
}
// Call Close when done reading.
reader.Close();
}
}
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.aspx
I would use something like this to get the column(s) you're after:
string username = null;
using (SqlDataReader reader = com.ExecuteReader()) {
if (reader.read()) {
username = (string)reader["mydbcolumnname"];
}
reader.Close();
}
Note that if you want to pull all the result rows (as opposed to stepping through them) then you'd normally use a SqlDataAdapter to fill a DataSet (instead of the reader), eg:
string username;
using (SqlDataAdapter adapter = new SqlDataAdapter(com))
{
using (DataSet ds)
{
adapter.Fill(ds);
username = (string)ds.Tables[0].Rows[0]["mycolumnname"];
}
}
I'm all for easy; I would write a class that mirrors the record I'm reading, i.e.
public class User {
public int Id {get;set;}
public string Name {get;set;}
}
and use "dapper":
var user = myCon.Query<User>(
"SELECT * FROM tbl_tiduser WHERE username=#username AND stat not in ('1','4')",
new {username}).SingleOrDefault();
if(user == null) { /* not found, presumably throw an exception */ }
string name = user.Name; // etc
Then you don't need to mess with commands, readers, parameters etc (see how the username is being made into a db parameter cleanly?).
I'm using c# in a ASP.Net web application.I have the following query:
SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["chestionar"].ConnectionString);
con.Open();
SqlCommand cmd = new SqlCommand("select * from personal,Intrebari where personal.cod_numeric_personal=#cnp AND Intrebari.id_intrebare=14 AND Intrebari.id_intrebare=15 ", con);
cmd.Parameters.AddWithValue("#cnp", Session["sesiune_cnp"]);
SqlDataReader rdr;
rdr = cmd.ExecuteReader();
while (rdr.Read())
{
lbl1.Text = rdr["Nume"].ToString();
intrebare6.Text = rdr["Intrebari"].ToString();
intrebare7.Text = rdr["Intrebari"].ToString();
}
I want those two values for id_intrebare=14 and 15 to assign it to those 2 labels.How can i refer to those?
In order to read stuff from the reader you need to include it in the select statement for you sql, it is better to select it explicitly rather than use select *.
but you are not currently going to get any results returned because id_intrebare cannot be both 14 and 15
you then need to read id_intreabare ratherr than Intreabari.
Try this, notice the try catch block, I also changed your SQL query.
SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["chestionar"].ConnectionString);
string qry="select * from personal,Intrebari where personal.cod_numeric_personal=#cnp AND Intrebari.id_intrebare IN (14,15);
SqlCommand cmd = new SqlCommand(qry, con);
cmd.Parameters.AddWithValue("#cnp", Session["sesiune_cnp"]);
try
{
con.Open();
SqlDataReader rdr= cmd.ExecuteReader();
if(rdr.HasRows)
{
while (rdr.Read())
{
lbl1.Text = rdr["Nume"].ToString();
intrebare6.Text = rdr["Intrebari"].ToString();
intrebare7.Text = rdr["Intrebari"].ToString();
}
}
}
catch(SQLException ex)
{
lblStatus.Text="An error occured"+ex.Message;
throw ex;
}
finally
{
con.Close();
con.Dispose();
}
If you want to assign texts to different numbered lables in a loop, you can refer to the control id with FindControl of the current page
int numeOrdinal = reader.GetOrdinal("Nume");
int intrebariOrdinal = reader.GetOrdinal("Intrebari");
int i = 1;
while (rdr.Read()) {
// Nume (Romanian) = Name
page.FindControl("lbl" + i).Text = reader.IsDBNull(numeOrdinal)
? ""
: rdr.GetString(numeOrdinal);
// Intrebari (Romanian) = Question
page.FindControl("intrebari" + i + 5).Text = reader.IsDBNull(intrebariOrdinal)
? ""
: rdr.GetString(intrebariOrdinal);
i++;
}
Try using cmd.ExecuteScalar it will return the first reuslt it finds so you have to define your conditions well. Also it returns object type so you will have to cast the result