I have a problem with my SQL datareader, i want to make an external class and make the code in my xaml.cs as short as possible, because there are a lot of sqldatareaders needed in my program. for this I want to pass following two strings to the datareader class:
public void refreshcombobox()
{
cbGebruiker.Items.Clear();
database = new DataBase();
string sqlrdr = "(rdr.GetString(1).ToString().Trim())";
List<string> reader = database.ReaderRdr("Select * from Gebruikers", ref sqlrdr);
foreach (String str in reader)
{
cbGebruiker.Items.Add(str);
}
}
however, when I do this this is the result in my program instead of the actual results that are stored in the database:
http://i58.tinypic.com/301j2vo.jpg (I can't post images)
can somebody help me with this? I've searched everywhere...
I don't know how to pass the rdr.GetString(1).ToString().Trim() to make it actually look stuff up in the db. Instead of just copying the string directly into the list.
This is the class:
namespace ClassLib
{
public class DataBase
{
SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["kassadatabase"].ConnectionString);
public object ScalarObject(string sql)
{
object value = null;
try
{
conn.Open();
SqlCommand cmd = new SqlCommand(sql, conn);
value = cmd.ExecuteScalar();
}
catch (SqlException ex)
{
MessageBox.Show(ex.Message);
}
finally
{
if (conn != null) conn.Close();
}
return value;
}
public List<string> ReaderRdr(string sql)
{
SqlDataReader rdr = null;
List<string> reader = new List<string>();
try
{
conn.Open();
SqlCommand cmd = new SqlCommand(sql, conn);
rdr = cmd.ExecuteReader();
while (rdr.Read())
{
//reader.Add(rdr.GetString(1).ToString().Trim());
}
}
catch (SqlException ex)
{
MessageBox.Show(ex.Message);
}
finally
{
if (rdr != null) rdr.Close();
if (conn != null) conn.Close();
}
return reader;
}
//public List<string> ReaderRdr(string sql, ref string str)
//{
// SqlDataReader rdr = null;
// List<string> reader = new List<string>();
// try
// {
// conn.Open();
// SqlCommand cmd = new SqlCommand(sql, conn);
// rdr = cmd.ExecuteReader();
// while (rdr.Read())
// {
// //MessageBox.Show(str.ToString());
// //var strRdr = str;
// //MessageBox.Show(strRdr.ToString());
// //reader.Add(rdr.GetString(1).ToString().Trim());
// reader.Add(str);
// Console.WriteLine(String.Format("{0}", rdr[0]));
// }
// }
// catch (SqlException ex)
// {
// MessageBox.Show(ex.Message);
// }
// finally
// {
// if (rdr != null) rdr.Close();
// if (conn != null) conn.Close();
// }
// return reader;
//}
public void ExecuteNQuery(string insertString)
{
try
{
conn.Open();
SqlCommand cmd2 = new SqlCommand(insertString, conn);
cmd2.ExecuteNonQuery();
}
catch (SqlException ex)
{
MessageBox.Show(ex.Message);
}
finally
{
if (conn != null) conn.Close();
}
}
}
}
public List<string> ReaderRdr(string sql)
{
SqlDataReader rdr = null;
List<string> reader = new List<string>();
try
{
conn.Open();
SqlCommand cmd = new SqlCommand(sql, conn);
rdr = cmd.ExecuteReader();
while (rdr.Read())
{
//reader.Add(rdr.GetString(1).ToString().Trim());
}
.....
now in the methode public list i want to replace the //reader.Add(rdr.GetString(1).ToString().Trim()); part(wich works fine)
with a string that is passed to the method.
public List<string> ReaderRdr(string sql, string strRdr)
{
SqlDataReader rdr = null;
List<string> reader = new List<string>();
try
{
conn.Open();
SqlCommand cmd = new SqlCommand(sql, conn);
rdr = cmd.ExecuteReader();
while (rdr.Read())
{
//reader.Add(strRdr);
}
I'm not 100% sure what you're trying to do, but I can tell you right now that this is what you're doing wrong - the string (str) you're passing to ReaderRdr is just a string literal of C# code. There's super hacky (super inadvisable) things you can do to mimic what exists in other languages as eval(), but there's no built-in way to do that in C#. Nothing (sensible) you do to "(rdr.GetString(1).ToString().Trim())" is ever going to get a string, or cast it to string, or trim anything.
Within your ReaderRdr function, all you're accomplishing is just to add the string str to your List<string> reader. This accomplishes nothing and has no bearing whatsoever on the results you get from your database query in your SqlDataReader rdr. If you want to store the data you actually get from your database, use rdr, not the (useless) string argument str.
Also, I feel like you must have left something out of your code - you're instantiating your SqlCommand cmd with conn as your second argument, but I don't see that defined anywhere within your ReaderRdr method, and it's not an argument passed to ReaderRdr. You don't have an SqlConnection object as a field or property within your class, do you?
As far as what you should maybe do, despite lacking much of any context in terms of your actual aims - if you want to get any given column of the result for each row returned by your SqlDataReader:
rdr = cmd.ExecuteReader();
while (rdr.Read())
{
var yourDataCell = rdr[yourColumnIndex];
// or:
var yourDataCellOtherWay = rdr["YourColumnName"];
}
Alternately, you can just iterate through each of the cells in any given row produced by your SqlDataReader like so:
for(int i = 0 ; i < numberOfColumns; i++) {
// do something with rdr[i] here
}
I'm not sure if there's anything you can do establish numberOfColumns based on the state of your SqlDataReader, but others might know better.
You actually adding the String that you passed to a function to your reader reader.Add(str); You get the response from SQL I your rdr.
This item will show you something from your database:
Console.WriteLine(String.Format("{0}", rdr[0]));
Related
I need to write a C# program and it has to be able to manage my data on my server. I have an NPGSQL server set up with a data table, I can write data into it, but I just can't get to read the data while running a program.What do I do wrong?
public NpgsqlDataReader reader;
public NpgsqlCommand InsertCommand = new NpgsqlCommand();
public String sConnectionString;
public Npgsql.NpgsqlConnection Conn;
public void DataBaseOpen()
{
sConnectionString = "Server=192.168.1.100;Port=5432;Username=postgres;Password=admin;Database=analoginput;Pooling=false;MinPoolSize=1;MaxPoolSize=999;Timeout=15;";
Conn = new Npgsql.NpgsqlConnection(sConnectionString);
InsertCommand = Conn.CreateCommand();
Conn.Open();
}
public void DataBaseClose()
{
Npgsql.NpgsqlConnection.ClearAllPools();
Conn.Close();
}
InsertCommand.CommandText = "Select * From public.sensorlog WHERE \"date\" > '2019.07.08.' And \"date\" < '2019.07.10.' order by Date asc;";
System.Windows.MessageBox.Show(InsertCommand.CommandText);
Npgsql.NpgsqlDataReader reader = InsertCommand.ExecuteReader();
System.Data.DataTable CSV = new System.Data.DataTable();
while (reader.Read())
{
CSV.Load(reader);
}
I want to load the data into the CSV datatable, but I just can't get it to work. The datatable is just empty.
What if you refactor your code to something like below.
The using statement will guarantee that your connection & command is closed/disposed when it goes out of scope and with the try/catch block you will catch any exceptions and report it to the UI via messagebox. This will assist in capturing exceptions if there are any.
public Npgsql.NpgsqlConnection DatabaseOpen()
{
var sConnectionString = "Server=192.168.1.100;Port=5432;Username=postgres;Password=xxx;Database=analoginput;Pooling=false;MinPoolSize=1;MaxPoolSize=999;Timeout=15;";
var Conn = new Npgsql.NpgsqlConnection(sConnectionString);
Conn.Open();
return Conn;
}
public void Main()
{
try
{
using (var conn = DatabaseOpen())
{
using (var InsertCommand = conn.CreateCommand())
{
InsertCommand.CommandText = "Select * From public.sensorlog WHERE \"date\" > '2019.07.08.' And \"date\" < '2019.07.10.' order by Date asc;";
System.Windows.MessageBox.Show(InsertCommand.CommandText);
Npgsql.NpgsqlDataReader reader = InsertCommand.ExecuteReader();
System.Data.DataTable CSV = new System.Data.DataTable();
while (reader.Read())
{
CSV.Load(reader);
}
}
}
}
catch (Exception ex)
{
System.Windows.MessageBox.Show(ex.Message);
}
finally
{
Npgsql.NpgsqlConnection.ClearAllPools();
}
}
I currently have a DB library used for database access and I use it across several projects. I currently use the following code to get a recordset.
METHODS
public static IDataReader GetRs(string sql)
{
using (var con = NewSqlConnection())
{
con.Open();
return GetRs(sql, con);
}
}
public static IDataReader GetRs(string sql, SqlConnection dbconn)
{
using (var cmd = new SqlCommand(sql, dbconn))
{
int tries = 1;
while (tries <= 3)
{
try
{
if (dbconn.State == ConnectionState.Closed)
{
dbconn.Open();
}
DataTable myTable = new DataTable();
var reader = cmd.ExecuteReader();
myTable.Load(reader);
return myTable.CreateDataReader();
//return cmd.ExecuteReader();
}
catch (SqlException ex)
{
if (ex.Message.Contains("Timeout expired") || ex.Number == 1205) // Deadlock
{
Thread.Sleep(1000);
if (tries == 3)
{
throw ex;
}
tries += 1;
cmd.CommandTimeout *= 10;
}
else
{
throw ex;
}
}
}
}
throw new Exception("Could not get RecordSet");
}
USAGE
public static void Test()
{
using(var reader = GetRs("SELECT Col FROM TABLE"))
{
while(reader.Read())
{
// do stuff with data here e.g. var value = reader[0];
}
}
}
While this method works, as you can see it loads the entire dataset into memory thus causing issues with scaling.
I tried replacing the following code in the GetRs(string sql, SqlConnection con) method
DataTable myTable = new DataTable();
var reader = cmd.ExecuteReader();
myTable.Load(reader);
return myTable.CreateDataReader();
and tried returning just the return cmd.ExecuteReader();
However an error is thrown on the while (reader.Read()) - Invalid attempt to call read when the reader is closed. I am guessing this is because the SqlConnection property is disposed (and hence closed) after returning the IDataReader.
I'm aware that I can wrap the GetRs method with a new sql connection but this means rewriting a lot of my code, and I was hoping that I would be able to dispose the reader AND the connection with my using(var reader = GetRs()) method.
Is there any way I can still use these methods without loading the whole dataset into memory?
You can inject in your code with a Action<DataTableReader> parameter to you GetRs call.
Try this:
public static void GetRs(string sql, Action<DataTableReader> consumer)
{
using (var con = NewSqlConnection())
{
con.Open();
GetRs(sql, con, consumer);
}
}
public static void GetRs(string sql, SqlConnection dbconn, Action<DataTableReader> consumer)
{
using (var cmd = new SqlCommand(sql, dbconn))
{
if (dbconn.State == ConnectionState.Closed)
{
dbconn.Open();
}
DataTable myTable = new DataTable();
var reader = cmd.ExecuteReader();
myTable.Load(reader);
consumer(myTable.CreateDataReader());
}
}
(I removed your try/catch code for clarity.)
Then you call it like this:
public static void Test()
{
GetRs("SELECT Col FROM TABLE", reader =>
{
while(reader.Read())
{
// do stuff with data here e.g. var value = reader[0];
}
});
}
Your connection object was closed by the following line
using (var con = NewSqlConnection())
{
con.Open();
return GetRs(sql, con);
}//Connection object gets released here
But still, you are returning the reader object which was created by SqlCommand object using the above connection object. Hence the reader object is closed.
I would like to find a way to exit out of datareader after the if statement so that I can execute the insert query in else statement. Is there a way to do it?
I am getting the error that dr is still open and hence cannot perform the below query.
sVendorDetails.VendorID = insertcmd.ExecuteNonQuery();
Here is the code:
public class VendorDetails
{
int _VendorID;
string _VendorName;
public int VendorID
{
set { _VendorID = value; }
get { return _VendorID; }
}
public string VendorName
{
set { _VendorName = value; }
get { return _VendorName; }
}
}
public VendorDetails VendorCheck(string sVendorName)
{
SqlCommand cmd = new SqlCommand("dbo.usp_GetVendorByVendorName", myConnection);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add(new SqlParameter("#VendorName", SqlDbType.VarChar));
cmd.Parameters["#VendorName"].Value = sVendorName;
VendorDetails sVendorDetails = null;
try
{
myConnection.Open();
SqlDataReader dr = cmd.ExecuteReader();
if (dr.HasRows)
{
while (dr.Read())
{
sVendorDetails = new VendorDetails();
sVendorDetails.VendorID = ((int)dr["VendorID"]);
sVendorDetails.VendorName = ((string)dr["VendorName"]).ToUpper().Trim();
}
}
else if (dr.HasRows!= true)
{
ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('VendorName:" + sVendorName + " not found. Inserting Vendor details into Vendor and Invoice table.')", true);
SqlCommand insertcmd = new SqlCommand("dbo.InsertVendorName", myConnection);
insertcmd.CommandType = CommandType.StoredProcedure;
insertcmd.Parameters.Add(new SqlParameter("#VendorName", SqlDbType.VarChar));
insertcmd.Parameters["#VendorName"].Value = sVendorName;
sVendorDetails = new VendorDetails();
sVendorDetails.VendorID = insertcmd.ExecuteNonQuery();
sVendorDetails.VendorName = sVendorName;
}
dr.Close();
return sVendorDetails;
}
catch (SqlException err)
{
throw new ApplicationException("DB usp_GetVendorByVendorName Error: " + err.Message);
}
finally
{
myConnection.Close();
}
}
You will need to close/dispose of your DataReader prior to reusing the connection, as it's still being used.
Maybe something like this?
var readerHasRows = false;
using (var dr = cmd.ExecuteReader())
{
readerHasRows = dr.HasRows;
if(readerHasRows)
{
while (dr.Read())
{
sVendorDetails = new VendorDetails();
sVendorDetails.VendorID = ((int)dr["VendorID"]);
sVendorDetails.VendorName = ((string)dr["VendorName"]).ToUpper().Trim();
}
}
}
if(!readerHasRows)
{
ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('VendorName:" + sVendorName + " not found. Inserting Vendor details into Vendor and Invoice table.')", true);
SqlCommand insertcmd = new SqlCommand("dbo.InsertVendorName", myConnection);
insertcmd.CommandType = CommandType.StoredProcedure;
insertcmd.Parameters.Add(new SqlParameter("#VendorName", SqlDbType.VarChar));
insertcmd.Parameters["#VendorName"].Value = sVendorName;
sVendorDetails = new VendorDetails();
VendorDetails.VendorID = insertcmd.ExecuteNonQuery();
sVendorDetails.VendorName = sVendorName;
}
There are a few things I would like to mention
Your main issue is that you are not closing your DataReader. You can use the using statement for it
You don't need to explicitly open and close the SqlConnection. The SqlCommand object will do it as needed.
You don't need to check with if (dr.HasRows) and then check again in while (dr.Read()). Also, you don't need to loop to pick up only one row of data.
Ideally, I would put the "Fetch" part in a separate function and the "insert" in a separate function, so the functions stay small and reusable.
Your pattern is superfluous if (flag) {TakeAction();} else if (!flag) {TakeAction2();}. Every time the code hits theelse, it will also hit theif (!flag)`
sVendorDetails.VendorID = insertcmd.ExecuteNonQuery(); line looks fishy. If your Stored Procedure returns the VendorId, then you should use ExecuteScalar. Currently it is just storing 1 in all case since you are presumably inserting one row.
Don't discard the original SqlException when creating a custom ApplicationException. Upstream system might want to know more details than you are passing. Pass it along as the InnerException
I have also changed some stylistic aspects:
The variable names changed to the more commonly used camelCase, instead of the incorrectly used Hungarian Notation (sVendorDetails instead of oVendorDetails)
Brace in K&R style
Used var when the right side is a new statement
Use Object Initializers instead of creation+assignment
Below is the code
public VendorDetails VendorCheck(string vendorName, SqlConnection myConnection) {
try {
return GetVendor(vendorName, myConnection) ?? InsertVendor(vendorName, myConnection);
} catch (SqlException err) {
throw new ApplicationException("DB usp_GetVendorByVendorName Error: " + err.Message, err);
}
}
VendorDetails GetVendor(string vendorName, SqlConnection myConnection) {
using (var cmd = new SqlCommand("dbo.usp_GetVendorByVendorName", myConnection)) {
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add(new SqlParameter("#VendorName", SqlDbType.VarChar));
cmd.Parameters["#VendorName"].Value = vendorName;
using (SqlDataReader dr = cmd.ExecuteReader()) {
ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('VendorName:" + vendorName + " not found. Inserting Vendor details into Vendor and Invoice table.')", true); // TODO: Does this really belong here!?!?
if (dr.Read()) {
return new VendorDetails {
VendorID = ((int)dr["VendorID"]),
VendorName = ((string)dr["VendorName"]).ToUpper().Trim()
};
}
}
}
return null;
}
VendorDetails InsertVendor(string vendorName, SqlConnection myConnection) {
using (var insertcmd = new SqlCommand("dbo.InsertVendorName", myConnection)) {
insertcmd.CommandType = CommandType.StoredProcedure;
insertcmd.Parameters.Add(new SqlParameter("#VendorName", SqlDbType.VarChar));
insertcmd.Parameters["#VendorName"].Value = vendorName;
return new VendorDetails {
VendorID = (int)insertcmd.ExecuteScalar(),
VendorName = vendorName
};
}
}
I am attempting to get the data my connectionstring pulls in my C# class's to the appropriate data controls on my website. I have looked online how to go about doing this but no results. I figured it would be easy like C# and you just reference the control you want to fill in the .Net page. Any suggestions on how to get my data into my controls? I have posted my c# code to get the data.
load method:
public void load()
{
var sqlString = new StringBuilder();
sqlString.Append("SELECT CaseNum6, CaseNum9, Group, Completion ");
sqlString.Append("FROM WorkOrder ");
sqlString.Append("WHERE Group = 1 OR Group = 2 ");
sqlString.Append("AND Completion = 0 ");
SqlDataReader reader = null;
SqlConnection dbConn = DBHelper.getConnection();
SqlParameter[] parameters = new SqlParameter[] { new SqlParameter("#CaseNum6", CaseNum6 )};
try
{
reader = DBHelper.executeQuery(dbConn, sqlString.ToString(), parameters);
if (reader != null)
{
if (reader.Read())
{
CaseNum6 = (int)reader["CaseNum6"];
CaseNum9 = (int)reader["CaseNum9"];
Group = (int)reader["Group"];
Completion = (bool)reader["Completion"];
}
else
throw new Exception("No record returned");
reader.Close();
reader.Dispose();
dbConn.Close();
dbConn.Dispose();
}
}
DBHelper:
class DBHelper
{
private DBHelper() { }
public static SqlConnection getConnection()
{
return new SqlConnection(ConfigurationManager.ConnectionStrings["Connection"].ConnectionString);
}
public static SqlConnection getFRESHConnection()
{
return new SqlConnection(ConfigurationManager.ConnectionStrings["FRESHConnection"].ConnectionString);
}
public static SqlDataReader executeQuery(SqlConnection dbConn, string sqlString, SqlParameter[] parameters)
{
SqlCommand cmd = null;
SqlDataReader reader = null;
try
{
if (dbConn.State == ConnectionState.Closed)
dbConn.Open();
cmd = dbConn.CreateCommand();
cmd.CommandText = sqlString;
if (parameters != null)
{
cmd.Parameters.AddRange(parameters);
}
reader = cmd.ExecuteReader();
cmd.Dispose();
}
catch (Exception ex)
{
throw ex;
}
return reader;
}
}
Not sure what exactly is the issue. But to give an overview of how to add values to controls.
Drop a control from the toolbox into the web page(.aspx).
You will now be able to reference it in the code behind, and simply use something like
TextBox1.Text = "Hello World"; // TextBox1 is the id of the control
See more on MSDN docs
Get and Set values on Textboxes
Did not have the right file extension for background coding.
I'm implementing connection I implemented methods for Connect and Insert. Those methods are working. But I have problem how to implement getdata() method (get data from database). After I send query to the method and I need to know how to use SqlDataReader.
public String GetData(string _query)
{
try
{
SqlCommand cmd = new SqlCommand(_query, this.dbCon);
results = cmd.ExecuteReader().ToString();
return results;
}
catch (Exception)
{
return "Error";
}
}
I want to complete this get method, I'm using SQL Server and C#
Do not reinvent the wheel. Typed DataSets and EF are by far and away the best methods of retrieving and manipulating data in .NET for most scenarios. MS has already written all of what you are trying to write in a MUCH better way than you'll probably ever be able to achieve. The time you spend in learning these two technologies will give you long-lasting benefit. This is more true for you since you're using it against SQL Server.
This is a fairly straight forward example you can look at:
public SqlDataReader ExecuteReader(SqlCommand cmd)
{
return cmd.ExecuteReader();
}
Using this method, I could execute the following:
var reader = ExecuteReader(new SqlCommand("SELECT ColumnA, ColumnB FROM Table"));
string ColA = string.empty;
string ColB = string.empty;
while (reader.Read())
ColA = reader["ColumnA"].ToString();
ColB = reader["ColumnB"].ToString();
reader.Close();
reader.Dispose();
Try something like this:
private void TestMethod(string sqlCmd, List<string> myColumns)
{
try
{
SqlDataReader myReader = null;
SqlCommand myCommand = new SqlCommand(sqlCmd, myConnection);
myReader = myCommand.ExecuteReader();
while(myReader.Read())
{
foreach (var col in myColumns)
{
Console.WriteLine(myReader[col].ToString());
}
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
In addition you can take a look at this Article.
Write a method to get the data reader as below,
private SqlDataReader TestMethod(string sqlCmd, List<string> myColumns)
{
try{
SqlDataReader myReader = null;
SqlCommand myCommand = new SqlCommand(sqlCmd, myConnection);
myReader = myCommand.ExecuteReader();
return myReader;
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
And then just use it as,
SqlDataReader myReader = TestMethod("your query",youtcolumnlist)
while(myReader.Read())
{
foreach (var col in myColumns)
{
Console.WriteLine(myReader[col].ToString());
}
}