Pls Help... How Can I Retieve The Value Of Fields In My Sqldatabase Using Sqldatareader
Nov 6, 2007 Please help me with my thesis... I am using ASP.NET
How can I retieve the value of fields in my sqldatabase using sqldatareader
thnks
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Referencing Fields Returned By SqlDataReader
Apr 3, 2008In C#, when I'm using an SqlDataReader to run a simple select query and use the values returned I have a question about referencing the field values.
There seem to be a large number of "Get" type methods (i.e reader.GetValue(int i), etc.) All of them (that I have found so far, require the use of the index of the field (GetValue(0) is the first field and so on).
Is there a way to use the actual name of the field? (i.e. GetValue("myField"))? This helps code readability but the big reason is that changes to the underlying field list can completely hose up the application.
I know there are such functions in VB, but I just can't seem to find the equivelants in C#.
Encrypt, Store And Retieve Passwords From A Table
Oct 17, 2007Hi, Is it possible to store encryped user passwords in a table and be able to retieve them in readable form.
Thanks
SQLDATABASE ERROR HELP PLEASE
Dec 3, 2007
Hi, i got a problem with the SQL server now is displaying this error
INDEX #0 Message:the statement has been terminated. nativeError 3621 Source: Microsoft OLE DB provider for SQL server SQLState:01000 and the
Index #1 Message: String or binary data would be truncated. nativeError:8152
Source:Microsoft OLE DB provider for SQL server State : 220001
please help me
Importing Sqldatabase And Publishing It
Apr 20, 2007HI,
I am working on a project in which a user can upload his database to the server...then he is able to view all the schema or execute any kind of query. Then he goes to some other machine and login and wants to download the database.
For example Alex have uploaded the database consisting of 1000 records to mysite. Then He goes to texas to find some oil wells. He is on another machine ... I download the database .... inseert new records and upload it back.
Its an example basically I want to know how to include the users' uploaded into my sqlserver and when required publish with data on his machine...
Thanks.
How To Import Csv File Into Sqldatabase
Sep 26, 2007 Hi All,I have to import a csv file to sql database.I searched on the net and found plenty of exampls but all with msaccess database.I did not find any example with sql server.Can anybody have the code or the link?here is one example with msaccess
Dim cn As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data
Source=C:;Extended Properties=""Text;HDR=No;FMT=Delimited""")
Dim da As New OleDbDataAdapter()
Dim ds As New DataSet()
Dim cd As New OleDbCommand("SELECT * FROM C:Test.csv, cn)
cn.Open()
da.SelectCommand = cd
ds.Clear()
da.Fill(ds, "CSV")
dg.DataSource = ds.Tables(0)
cn.Close() but when i am using the sqlserver how to get csv data by setting extended properties .RegardsBrijesh Singh
How I Can Use SqlDataReader?
Nov 29, 2007Hi..
Every time I want to read any record from data base I read it in dataset for example:SqlConnection con = new SqlConnection(@"Data Source=localhost ;Initial Catalog=university ;Integrated Security=True");
SqlCommand cmd = new SqlCommand("select [User_AuthorityID] from users where [UserID]='" + TextBox1.Text + "' and [UserPassword]='" + TextBox2.Text + "' ", con);SqlDataAdapter adp = new SqlDataAdapter();
adp.SelectCommand = cmd;DataSet ds = new DataSet();
adp.Fill(ds, "UserID");foreach (DataRow dr in ds.Tables["UserID"].Rows)
{
user_type = dr[0].ToString();
Session.Add("User_AuthorityID", user_type);
.........
Is there easier way to read data from data base?
How I can use SqlDataReader to do that?
Thanks..
SqlDataReader Within Another SqlDataReader - Can It Be Done?
Jun 1, 2008Hey All,
I have come across a situation with two tables, they are dynamic and the user can add and edit values in the tables so I need to build a dynamic display control. It is all based around an FAQ system I have built. The user can create new FAQ categories (that is one table) then create a new FAQ Question & Answer (that is the second table). The tables are linked by the category id. So now I am trying to display the FAQ section like so.
CATEGORY NAME
QuestionAnswerQuestionAnswerCATEGORY NAME
QuestionAnswerQuestionAnswerCATEGORY NAME
QuestionAnswerQuestionAnswer
So my idea was to run a loop within a loop. First loop the category name, then within the category name, loop a second time to grab all of the questions & answers within the category id captured from the first loops sql select statement, then proceed to loop the category name again and of course repeat the process until all loops are completed. However I am getting, and I kinda figured I would get an error about my SQLDataReader. Bellow is my code maybe some type of edit or different recommendation is needed. Any help will do, thanks!Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
'--- Database Connection ---Dim sConnStr As String = ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString
Dim cnBKPost As New SqlConnection(sConnStr)
'--- End DB Connection ----
'----- FAQ's -------
Dim sql As String = "SELECT category_id, category_name FROM faq_category ORDER BY category_name DESC"Dim cmd As New SqlCommand(sql, cnBKPost)
cnBKPost.Open()Dim reader As SqlDataReader = cmd.ExecuteReader()
Dim str As New StringBuilder()
Dim catid As IntegerDo While reader.Read()
'--- Category Titles ----catid = reader("category_id")
str.Append("<h2>" & reader("category_name") & "</h2>")
'--- End Category Title ---
'--- Get FAQ's In Category ---
Dim sqlcat As String = "SELECT faq_question, faq_answer FROM tbl_faq WHERE faq_category = '" & catid & "'"Dim cmdcat As New SqlCommand(sqlcat, cnBKPost)
Dim readerfaq As SqlDataReader = cmdcat.ExecuteReader()Do While readerfaq.Read()
str.Append("<p><font style='font-size:12pt;font-color:#daa520;>'" & reader("faq_question") & "</font><br />")str.Append(reader("faq_answer") & "</p>")
str.Append("<br /><br /><br />")
Loop
readerfaq.Close()
'--- End Get FAQ's in Category ---
Loop
reader.Close()
cnBKPost.Close()Me.Literal1.Text = str.ToString()
End Sub
End Class
Using SqlDataReader
Jun 25, 2004i'm using c# and SqlDataReader to simply retrieve data from one column of a database. problem is it's an integer i'm trying to retrieve, and so i'm trying to put it into an int variable, and i get the error "CS0029: Cannot implicitly convert type 'object' to 'int'" . i've looked for an answer for about an hour and every example for the SqlDataReader that i can find deals with strings only or the examples are too complex for me to understand.
there must be an easy way to retrieve this data and put it into an integer! help...
my line of code that creates the error:
int intGuestNum = dtrSelectTotalSessions["online_numSessions"];
Rowcount And SQLDataReader
Aug 29, 2006Hi, from what I can find, there isn't a way to get the number of rows returned from a SQLDataReader command. Is this correct? If so, is there a way around this? My SQLDataReader command is as follows:Dim commandInd As New System.Data.OleDb.OleDbDataAdapter(strQueryCombined, connInd)Dim commandSQL As New SqlCommand("GetAssetList2", connStringSQL)Dim resultDS As New Data.DataSet()'// Fill the dataset with valuescommandInd.Fill(resultDS)'// Get the XML values of the dataset to send to SQL server and run a new queryDim strXML As String = resultDS.GetXml()Dim xmlFileList As SqlParameterDim strContainsClause As SqlParameter'// Create and execute the search against SQL ServerconnStringSQL.Open()commandSQL.CommandType = Data.CommandType.StoredProcedurecommandSQL.Parameters.Add("@xmlFileList", Data.SqlDbType.VarChar, 1000).Value = strXMLcommandSQL.Parameters.Add("@strContainsClause", Data.SqlDbType.VarChar, 1000).Value = strContainsConstructDim sqlReaderSource As SqlDataReader = commandSQL.ExecuteReader()results.DataSource = sqlReaderSourceresults.DataBind()connStringSQL.Close()And the stored procedure is such:DROP PROC dbo.GetAssetList2;GOCREATE PROC dbo.GetAssetList2(@xmlFileList varchar(1000),@strContainsClause varchar(1000))ASBEGINSET NOCOUNT ONDECLARE @intDocHandle intEXEC sp_xml_preparedocument @intDocHandle OUTPUT, @xmlFileListSELECT DISTINCTAssetsMaster.AssetMasterUID,SupportedFiles.AssetPath,FROM AssetsMaster, OPENXML (@intDocHandle, '/NewDataSet/Table',2) WITH (FILENAME varchar(256)) AS x,SupportedFilesWHEREAssetsMaster.AssetFileName = x.FILENAMEAND AssetsMaster.Extension = SupportedFiles.Extension UNIONSELECT DISTINCTAssetsMaster.AssetMasterUID,SupportedFiles.AssetPath,FROM AssetsMaster, OPENXML (@intDocHandle, '/NewDataSet/Table',2) WITH (FILENAME varchar(256)) AS x,SupportedFilesWHEREAssetsMaster.AssetFileName <> x.FILENAMEAND CONTAINS ((Description, Keywords), @strContainsClause)AND AssetsMaster.Extension = SupportedFiles.ExtensionORDER BY AssetsMaster.Downloads DESCEXEC sp_xml_removedocument @intDocHandle ENDGOHow can I access the number of rows returned by this stored procedure?Thanks,James
View 3 Replies View RelatedNo More Data In A SqlDataReader?
Feb 16, 2007How do I tell when there is no more data to read in a SQLDataReader?
For example, I have an open datareader that I pass into a function that MIGHT still have a valid row in it when it returns from the function. How do I tell? I can't do a read() because then that current record will go away. I need to be able to tell if there is a current record without doing another read.
TIA,
SqlDataReader.GetOrdinal()
Jun 18, 2007Say I have this SQL query running into an SqlDataReader select TaskName, TaskDescription from tblTasks where TaskID = 5 There are two different ways to get the data out of the reader (maybe more) TaskName.Text = Reader.GetString(0);andTaskName.Text = Reader.GetString(Reader.GetOrdinal("TaskName")); My question is, is there a major difference in terms of efficiency between these two? The second one is definitely more robuts (in a situation where you are calling a stored procedure, and the stored procedure might change, etc) but the first one has fewer operations. Is the increase in robustness of the second one worth the potential performance hit, if any? Thank you, -Madrak
View 2 Replies View RelatedWhat Is The Purpose Of Having SqlDataReader Here?
Jul 23, 2007May I know what is the purpose of having SqlDataReader in Example A? I can see the same output when I tried out both. Should I use Example A or Example B? Currently, I'm using Example B since it is lesser code.Example A Dim objDR As SqlDataReader 'Create Data Reader
LoginConn.Open()
strSQL = "SELECT CountryID, CountryName FROM Country ORDER BY CountryName "
cmd = New SqlCommand(strSQL, LoginConn) objDR = cmd.ExecuteReader() 'Populate the DataReader ddlNationality.DataSource = objDR ddlNationality.DataBind() ddlNationality.SelectedValue = dvUserProfile.Item(0)("Nationality")LoginConn.Close() Example BLoginConn.Open() strSQL = "SELECT CountryID, CountryName FROM Country ORDER BY CountryName " cmd = New SqlCommand(strSQL, LoginConn) ddlNationality.DataSource = cmd.ExecuteReader() 'Populate the DataReader ddlNationality.DataBind() ddlNationality.SelectedValue = dvUserProfile.Item(0)("Nationality")LoginConn.Close()
Question About SqlDataReader....
Dec 31, 2007Hello every one and happy new year...
i have a problem with SqlDataReader used in asp.net application:
I defined a public object of SqlDataReader and assigned it the resultset of a query,
well, this happened ,lets say in page 1# but whan i want to use this datareader in another page
it keeps telling my that the reader is closed so i can't abstract information from, regarding that i used it's methods such "Read()" and "NextResult()"
but there is no use, what should i do, help me please !!!!!?
SQLDataReader Problem
Jan 4, 2008Hello im fairly new to ASP.Net and have a problem with an Intranet Page I am creating. In this part of the page I want to retrive a value from an SQL Table based on criteria and then store it as a variable to be used elsewhere on my page. I have tried using the SQL Data reader to retrive the value but somewhere in my code I am going wrong. Can anyone advise me on this please? See code below
My Visual Studio debugger has point out that there is a problem with my r = cmd.ExecuteReader() line
Oh and the connection to my SQL database is opened further up the page from this code.
Dim strSQL As String = "SELECT top 1 OrderID FROM tblStationeryOrder WHERE ORDERMADEBY = '" & lstUsers.SelectedValue & "' ORDER BY OrderID DESC"Dim cmd As New System.Data.SqlClient.SqlCommand
cmd.CommandText = strSQLDim r As System.Data.SqlClient.SqlDataReader
r = cmd.ExecuteReader()Do While r.Read()
Dim OrderID As Integer = r!OrderID
Exit Do
SqlDataReader Problems
Apr 25, 2008I found this tutorial at C# Station called "Reading Data with the SqlDataReader".
In my code behind file I followed what I think the tutorial was telling me to do but I keep getting a syntax error near '='
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Data.SqlClient.SqlException: Line 1: Incorrect syntax near '='. (Line 45: rdr = cmd.ExecuteReader();)
Heres my code:
protected void Page_Load(object sender, EventArgs e) { this.lblDate.Text = DateTime.Today.ToString("d"); string username; username = Convert.ToString(Session["usr"]); SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["csSecurity"].ConnectionString); SqlDataReader rdr = null; SqlCommand cmd = new SqlCommand("SELECT PROG_OFF FROM Logon_Table WHERE usr = " + username, conn); try { conn.Open(); rdr = cmd.ExecuteReader(); }
Any suggestions here would be great. Any links to tutorials you know of would be helpful also.
Thanks
Dim Rd As SqlDataReader Error
May 18, 2008good afternoon everybody
this is my code: and their is an error ,,really dunno where and why coz it seems logical to me :)Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
If RadioButton1.Checked = True Then
Dim admin As Stringadmin = "SELECT * from ADMINISTRATOR where UserName='" & TextBox1.Text & "' and UserPassword='" & TextBox2.Text & "'"
Dim sConnect As String = "Data Source=.SQLEXPRESS;AttachDbFilename=|DataDirectory|Database.mdf;Integrated Security=True;User Instance=True"Dim cnt As New SqlConnection
cnt.ConnectionString = sConnect
cnt.Open()Dim com As New SqlCommand
com.Connection = cnt
com.CommandText = adminerror!!>>>>Dim rd As SqlDataReader
rd = com.ExecuteReader
If rd.Read ThenSession("admn") = rd("UserName")Session("id") = rd("UserID")
rd.Close()
cnt.Close()Response.Redirect("~/adminpage.aspx")
ElseSession("admn") = 0
Label3.Visible = True
rd.Close()
cnt.Close()
End If
Else
Dim instrct As Stringinstrct = "SELECT * from instructor where name='" & TextBox1.Text & "' and passs='" & TextBox2.Text & "'"
Dim sConnect As String = "Data Source=.SQLEXPRESS;AttachDbFilename=|DataDirectory|Database.mdf;Integrated Security=True;User Instance=True"Dim con As New SqlConnection
con.ConnectionString = sConnect
con.Open()Dim com As New SqlCommand
com.Connection = con
com.CommandText = instrctDim r As SqlDataReader
r = com.ExecuteReader
If r.Read ThenSession("inst") = r("inst_name")
r.Close()
con.Close()Response.Redirect("~/instructorpage.aspx?id=" & Session("inst"))
ElseSession("inst") = 0
Label3.Visible = True
r.Close()
con.Close()
End If
End If
End Sub
-----------------
this is the error line:
The data types text and varchar are incompatible in the equal to operator.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Data.SqlClient.SqlException: The data types text and varchar are incompatible in the equal to operator....
so,,,any suggestions?
SQLdataReader Getting Closed
Jun 7, 2008I have an sp, which has 2 select statements, so iam using a sqldatareader and binding the data to a dropdown.
the first binding is fine, but when i say dataReader.NextResult(), It is null.It says the reader is closed. Can any one tell a work around for this.
thanx in advance,
Anil Kumar.
I Have Problem!! About SqlDataReader
Jun 10, 2008see ths code. please
== DAL ==
public static SqlDataReader ExecuteReader(SqlParameter param, string sp) { using (conn = new SqlConnection(connectString)) { SqlDataReader sdr = null; try { conn.Open();
comm = new SqlCommand(); comm.CommandText = sp; comm.CommandType = CommandType.StoredProcedure; comm.Connection = conn; comm.Parameters.Add(param); sdr = comm.ExecuteReader(CommandBehavior.CloseConnection); } catch(SqlException e) { WriteToLog(e.Message); } return sdr; } }
and, call above ExecuteReader() flowing this,
== BL ==
public UserEntity GetUserInformation(string UID, string sp) { UserEntity ue = new UserEntity();
SqlParameter userUID = new SqlParameter("@USR_ID", SqlDbType.VarChar, 20); userUID.Value = UID;
using (SqlDataReader sdr = DbHelper.ExecuteReader(userUID, "SP_GETUSERINFORMATION")) { if (sdr != null) { while (sdr.Read()) { ue.UserId = sdr["lecture_usr_id"].ToString(); ue.UserName = sdr["lecture_usr_realname"].ToString(); ue.Email = sdr["lecture_usr_email"].ToString(); ue.Phone = sdr["lecture_usr_phone"].ToString(); ue.Lastlogin = (DateTime)sdr["lecture_usr_lastlogin"]; ue.SignDate = (DateTime)sdr["lecture_usr_signdate"]; } } return ue; } }
error message is,
Invalid attempt to call Read when reader is closed.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.InvalidOperationException: Invalid attempt to call Read when reader is closed.Source Error:
Line 77: if (sdr != null)
Line 78: {
Line 79: while (sdr.Read())
Line 80: {
Line 81: ue.UserId = sdr["lecture_usr_id"].ToString();Source File: C:Users
aphyrDocumentsVisual Studio 2008ProjectslectureBusinessLogicUserManager.cs Line: 77
I can't understand!!! I try to debuging!!! but, I don't know.
please help me!
Question About SqlDataReader
Jun 14, 2008suppose I have a data reader which is returned by excuting a command "SELECT [xxx], [yyy], FROM [zzz]" , then I reads the data as normal. while I am reading , there is another thread that excute an insert command to that table , does this insertion effect the order of data that I am reading?
View 5 Replies View RelatedSqlDataReader And Tinyint
Apr 17, 2005I have an SP that returns a result set that contains a tinyint. My problem is that, when I try and access this value using GetInt16 (or 32), I get an error saying that "Specified cast is not valid". TinyInt is 1 byte, or 8 bits. GetInt16 'Gets the value of the specified column as a 16-bit unsigned integer'. I am assuming that this is the root cause of my problem. But, there doesn't seem to be a GetInt8 ?! Any ideas?
Thanks, Martin
Trouble With SqlDataReader
Jan 29, 2006hi..i am kind of new to asp.net n having trouble with the SqlException error message.. n this code works as 1st page pass the id to second page and the second page took the id to execute the query..i dun know the wer the error occurs..can give a help..Thanks.
private void Page_Load(object sender, System.EventArgs e)
{
SqlConnection connection = null;
SqlCommand command = null;
string sqlConnection = null;
string sql = null;
string ab = null;
sqlConnection = ConfigurationSettings.AppSettings["MSQLConnectionString"];
connection = new SqlConnection(sqlConnection);
if (!Page.IsPostBack)
{
try
{
if (Request.QueryString["categoryID"] == null)
{
}
else
{
ab= Request.QueryString["categoryID"].ToString(); //getting the id from page that pass this values
sql = "Select groupname, categoryid, description from groups where groups.categoryid=?"; // can this query execute?
command = new SqlCommand(sql, connection);
connection.Open();
command.Parameters.Add(new SqlParameter("categoryid", ab));
reader = command.ExecuteReader(); // error on here "SqlException"
while (reader.Read())
{
group.InnerText = reader["groupname"].ToString();
desc.InnerText = reader["description"].ToString();
}
}
}
finally
{
if (reader != null)
{
reader.Close();
}
if (connection != null)
{
connection.Close();
}
}
}
Subreports: Parameter Value Dropdown Shows Sum And Count Fields But Not The Actual Data Fields.
Jan 28, 2008
I have just started using SQL Server reporting services and am stuck with creating subreports.
I have a added a sub report to the main report. When I right click on the sub report, go to properties -> Parameters, and click on the dropdown for Parameter Value, I see all Sum and Count fields but not the data fields.
For example, In the dropdownlist for the Parameter value, I see Sum(Fields!TASK_ID.Value, "AppTest"), Count(Fields!TASK_NAME.Value, "CammpTest") but not Fields!TASK_NAME.Value, Fields!TASK_ID.Value which are the fields retrieved from the dataset assigned to the subreport.
When I manually change the parameter value to Fields!TASK_ID.Value, and try to preview the report, I get Error: Subreport could not be shown. I have no idea what the underlying issue is but am guessing that it's because the field - Fields!TASK_ID.Value is not in the dropdown but am trying to link the main report and sub report with this field.
Am I missing something here? Any help is appreciated.
Thanks,
Sirisha
Creating A Table In SQL Server With Fields From Other Tables And Some Fields User Defined
Feb 20, 2008How can I create a Table whose one field will be 'tableid INT IDENTITY(1,1)' and other fields will be the fields from the table "ashu".
can this be possible in SQL Server without explicitly writing the"ashu" table's fields name.
Public Overridable ReadOnly Default Property Fields() As ADODB.Fields
Jan 26, 2008sir
I have got this error message to establish connction with recordset vb .net, Can you please rectify this
Too many arguments to 'Public Overridable ReadOnly Default Property Fields() As ADODB.Fields'
my code like this
rs = New ADODB.Recordset
rs.Open("Select * from UserLogin where userid='" & txtUserName.Text & "'", gstrDB, DB.CursorTypeEnum.adOpenStatic)
If txtUserName.Text = rs.Fields.Append(userid) Then
MsgBox("OK", MsgBoxStyle.OKOnly, "Confirmation")
End If
thanks
Sqldatareader Not Returning Records
Feb 13, 2007My query is as follows:Dim CurrentDate As DateCurrentDate = "09/02/2007" MyCommand = New SqlCommand("SELECT RegisterID FROM Registers WHERE RegisterDate = @RegisterDate AND IsMorningRegister = 1", MyConn)MyCommand.Parameters.Add("@RegisterDate", Data.SqlDbType.DateTime)MyCommand.Parameters("@RegisterDate").Value = CurrentDate My DB table is called RegisterDate and is of type DateTime. The record that should be matched is: Register ID: 13 RegisterDate: 09/02/2007 09:00:00IsMorningRegister: TrueIsAfternoonRegister: False But no records are returned. Any idea why?
View 4 Replies View RelatedSqlDataReader + Stored Procedure
Feb 28, 2007I am trying to access data using this code:
SqlCommand myCommand = new SqlCommand("myStoredProcedure", myConnection);
myCommand.CommandType = CommandType.StoredProcedure;
myCommand.Parameters.Add(new SqlParameter("@myID", SqlDbType.Int));
myCommand.Parameters["@myID"].Value = myIDValue;
myConnection.Open();
myDataReader = myCommand.ExecuteReader();
myTextBox.Text = myDataReader["myColumn"].ToString();
myDataReader.Close();
myConnection.Close();
I get "data reader has no data" error.
A problem with the parameter?
The stored procedure returns a row when executed from the database explorer.
I have used datasets and table adapters up to now as in the data access tutorial on this site
Any Ideas?
Thanks
Mapping Of Columns In SqlDataReader
Mar 14, 2007Hi,I use SqlDataReader to read one row from database and than set some properties to values retrieved like this:string myString = myReader.GetValue(0) // this sets myString to first value in a rowIf, however, I change order of columns returned by stored procedure myString would be set to wrong value. Is there a way to do something like this: string myString = myReader.GetValue["ColumnName"];
View 7 Replies View RelatedSqldatareader Reads From Second Row Skip The First Row.
Jun 20, 2007Hello,
im using sqldatareader to read my data and whenever time i loop through the reader it starts from second row why is that?
here is my code:while (reader.Read()){hinfo.Name = reader["_name"].ToString();hi.Add(hinfo);}
i look at the database and i have two rows but its reading only the second row, skiping the first row
NULLReferenceException From SqlDataReader.GetValue()
Aug 23, 2007I am getting a random exception coming out of ADO.NET's SqlDataReader that I can't seem to track down for the life of me. I have put SQL Server and IIS under heavy load, with neither giving me the exceptions except occasionally (they come when there is no load as well). Web Site is built in VS2005 using .NET 2.0.
Basically, I have a web page that caches a few tables from a SQL database (about 10 tables are loaded into cache from this page) and the error can come from any of the tables while they are being read from the database randomly. I had assumed it was possible that a timeout was occuring while reading the data but from what the brief results google shows, there would be a different exception thrown it a timeout had occured.
Here is the exception that is showing up:
System.NullReferenceException: Object reference not set to an instance of an object. at System.Data.SqlClient.SqlDataReader.ReadColumnHeader(Int32 i) at System.Data.SqlClient.SqlDataReader.ReadColumn(Int32 i, Boolean setTimeout) at System.Data.SqlClient.SqlDataReader.GetValueInternal(Int32 i) at System.Data.SqlClient.SqlDataReader.GetValue(Int32 i) at Library.Data.DataProxy.ExecuteStoredProcedure(ArrayList& returnValues, TypeFactory factory)
I got the following exception once from the same section of code as well:
System.InvalidOperationException: Invalid attempt to FieldCount when reader is closed. at System.Data.SqlClient.SqlDataReader.get_FieldCount() at Library.Data.DataProxy.ExecuteStoredProcedure(ArrayList& returnValues, TypeFactory factory)
The code generating these errors is on line 29 below:
1 /// <summary>2 /// Executes a stored procedure that returns values3 /// </summary>4 /// <param name="returnValues">An arraylist of Types</param>5 /// <param name="factory">The Type specific factory</param>6 /// <returns>True if successful, false otherwise</returns>7 public bool ExecuteStoredProcedure(out ArrayList returnValues, TypeFactory factory)8 {9 bool bResult = true;10 SqlDataReader reader = null;11 12 returnValues = new ArrayList();13 MenseType nextType = null;14 15 try16 {17 // Open database connection18 OpenConnection();19 20 // execute SP21 reader = m_sqlCommand.ExecuteReader();22 23 while(reader.Read())24 {25 nextType = factory.CreateInstance();26 27 for(int i = 0; i < reader.FieldCount; i++)28 {29 object val = reader.GetValue(i);30 31 if(DBNull.Value == val)32 val = null;33 34 nextType.SetValue(reader.GetName(i), val);35 }36 37 returnValues.Add(nextType);38 39 } // while40 41 } // @ try42 catch(Exception ex)43 {44 returnValues = null;45 m_LastError = ex.ToString();46 bResult = false;47 48 #if(DEBUG)49 Library.IO.Logging.AddSQLMessage(ex);50 #endif51 52 } // @ catch53 finally54 {55 // close the reader if nessessary56 if (null != reader)57 reader.Close();58 59 // close db connection60 CloseConnection();61 62 } // @ finally63 64 return bResult;65 66 } // ExecuteStoredProcedure()
Any input would be greatly appreciated.
How To Reorder A SqlDataReader Object
Oct 5, 2007I have a SqlDataReader object that has some records:
1 hello12 hello23 hello3
Is there a fast/easy way to reorder them?
3 hello32 hello21 hello1
Sqldatareader Within A Loop From Another Reader?
Dec 26, 2007I have an SqlDataReader which loops through records returned from an SP, within that loop I would like to initiate another SP, but for some darn reason the following code won't work: // create SqlConnection object
string ConnectionString = ConfigurationManager.ConnectionStrings["aiv3cs"].ConnectionString;
SqlConnection myConnection = new SqlConnection(ConnectionString);
try
{
// Create a new XmlTextWriter instance
XmlTextWriter writer = new
XmlTextWriter(Server.MapPath("products.sitemap"), Encoding.UTF8);
writer.WriteStartDocument();
writer.WriteStartElement("siteMap");
writer.WriteAttributeString("xmlns", "http://schemas.microsoft.com/AspNet/siteMap-File-1.0");
// create the command
SqlCommand myCommand = new SqlCommand();
myCommand.Connection = myConnection;
// set up the command
myCommand.CommandText = "spGetMenuStructure";
myCommand.CommandType = CommandType.StoredProcedure;
// open the connection
myConnection.Open();
// run query
SqlDataReader myReader = myCommand.ExecuteReader();
bool HasSubElements = false;
SqlCommand myCommand2 = new SqlCommand();
SqlParameter myParameter1 = new SqlParameter();
SqlDataReader myReader2 = new SqlDataReader();
// parse the results
while (myReader.Read())
{
// create the command
myCommand2.Connection = myConnection;
// set up the command
myCommand2.CommandText = "spGetMenuSubElements";
myCommand2.CommandType = CommandType.StoredProcedure;
myParameter1.ParameterName = "@ContentID";
myParameter1.SqlDbType = SqlDbType.Int;
myParameter1.Value = Convert.ToString(myReader["ID"]);
myCommand2.Parameters.Add(myParameter1);
// run query
myReader2 = myCommand2.ExecuteReader();
while (myReader2.Read())
{
HasSubElements = true;
}
myReader2.Close();
if (Convert.ToString(myReader["HasPage"]) == "1")
{
writer.WriteStartElement("siteMapNode");
writer.WriteAttributeString("title", Convert.ToString(myReader["PageTitle"]));
writer.WriteAttributeString("description", Convert.ToString(myReader["PageTitle"]));
string PageURL = Convert.ToString(myReader["PageName"]) + "?ContentID=" + Convert.ToString(myReader["ID"]);
writer.WriteAttributeString("url", PageURL);
if (HasSubElements)
{
writer.WriteEndElement();
}
}
else
{
writer.WriteStartElement("siteMapNode");
writer.WriteAttributeString("title", Convert.ToString(myReader["PageTitle"]));
writer.WriteAttributeString("description", Convert.ToString(myReader["PageTitle"]));
}
HasSubElements = false;
}
myReader.Close();
// end the xml document and close
writer.WriteEndElement();
writer.WriteEndDocument();
writer.Close();
}
finally
{
myConnection.Close();
}I've gotten the following two errors:There is already an open DataReader associated with this Command which must be closed first.And a build error:Error29The type 'System.Data.SqlClient.SqlDataReader' has no constructors defined Any suggestions would be most appreciated.
[Almost Resolved] SqlDataReader Vs. DataSets
Feb 1, 2008Hi,
I am pretty new to harcore ASP.NET and .NET in general but I know the basics of the language and stuff like that. Basically I used to be a hardcore object pascal Delphi developer doing Windows Applications but have now moved to .NET world. The reason I posted this question here is I couldn't find any other specific place to ask so here it goes.
To get me started with good programming source and practices I downloaded the ASP.NET TimeTracker Starter Kit and after some modificaion in connection string (using SQL 2005 Developer edition not the Express one) I have managed to make it work. Things done in there are pretty interesting way by using a delegate to retrieve data and present it using databound controls.
As much simple as it sounds I am more of a fan of not using too many databound controls except in dropdown box, list box and stuff like that. So basically I need to develop DataAccessLayer (DAL) in such a way that it's useful for both Windows and Web application. So with my research I found that I should be using DataSets in the DAL because they are serializable and thatz what Web Applications & Services love over using SqlDataReader. Other advantage of using DataSet is to use ForEach syntex over While Loop in SqlDataReaders. So below is some code I extracted from the TimeTracker Starter Kit to get me started.
I also noticed that the return result is a list array of certain object, in this case Category. So does it mean that it can be used in frontend using ForEach syntex? How can I convert the code below to use DataSets over SqlDataReader? Private Delegate Sub TGenerateListFromReader(Of T)(ByVal returnData As SqlDataReader, ByRef tempList As List(Of T))
Public Overrides Function GetAllCategories() As List(Of Category)
Dim sqlCmd As SqlCommand = New SqlCommand()
SetCommandType(sqlCmd, CommandType.StoredProcedure, SP_CATEGORY_GETALLCATEGORIES)
Dim categoryList As New List(Of Category)()
TExecuteReaderCmd(Of Category)(sqlCmd, AddressOf TGenerateCategoryListFromReader(Of Category), categoryList)
Return categoryList
End Function
Public Overrides Function GetCategoryByCategoryId(ByVal Id As Integer) As Category
If Id <= DefaultValues.GetCategoryIdMinValue() Then
Throw New ArgumentOutOfRangeException("Id")
End If
Dim sqlCmd As SqlCommand = New SqlCommand()
AddParamToSQLCmd(sqlCmd, "@CategoryId", SqlDbType.Int, 0, ParameterDirection.Input, Id)
SetCommandType(sqlCmd, CommandType.StoredProcedure, SP_CATEGORY_GETCATEGORYBYID)
Dim categoryList As New List(Of Category)()
TExecuteReaderCmd(Of Category)(sqlCmd, AddressOf TGenerateCategoryListFromReader(Of Category), categoryList)
If categoryList.Count > 0 Then
Return categoryList(0)
Else
Return Nothing
End If
End Function
Private Sub TGenerateCategoryListFromReader(Of T)(ByVal returnData As SqlDataReader, ByRef categoryList As List(Of Category))
Do While returnData.Read()
Dim actualDuration As Decimal = 0
If Not returnData("CategoryActualDuration") Is DBNull.Value Then
actualDuration = Convert.ToDecimal(returnData("CategoryActualDuration"))
End If
Dim category As Category = New Category(CStr(returnData("CategoryAbbreviation")), actualDuration, _
CInt(returnData("CategoryId")), CDec(returnData("CategoryEstimateDuration")), CStr(returnData("CategoryName")), _
CInt(returnData("ProjectId")))
categoryList.Add(category)
Loop
End Sub
Hope this makes sense. Sorry if I have posted this in a wrong section..!
Cheers,Nirav