Develop Reference

Debug "ResultView" showing "Enumeration yielded no results"?

I have applied breakpoint and when I click on query "ResultView" its showing data but when I click 2nd time then data is empty and its showing Enumeration yielded no results. It is strange, is there any cache issue or something else? Why it is showing empty when I click after 1 time, its just show data 1st time,
var connectionString = String.Format(#"
Provider=Microsoft.ACE.OLEDB.12.0;
Data Source={0};
Extended Properties=""Excel 12.0 Xml;HDR=YES""
", filePath);
//Creating and opening a data connection to the Excel sheet
using (var conn = new OleDbConnection(connectionString))
{
conn.Open();
var cmd = conn.CreateCommand();
cmd.CommandText = "select * from [الحيازات$]";
using (var rdr = cmd.ExecuteReader())
{
//LINQ query - when executed will create anonymous objects for each row
var query =
(from DbDataRecord row in rdr
select row).Select(x =>
{
//dynamic item = new ExpandoObject();
Dictionary<string, string> item = new Dictionary<string, string>();
for (int i = 0; i < x.FieldCount; i++)
{
string data = "" + rdr.GetName(i) + ":{'id':'" + rdr.GetName(i) + "','code':'" + rdr.GetName(i) + "','title':'" + rdr.GetName(i) + "','type':'text','response";
item.Add(data, x[i] + "}");
}
return item;
});
//Generates JSON from the LINQ query
json = JsonConvert.SerializeObject(query, Formatting.Indented).Replace("'", "\"");// break point here

See similar question. Inspecting with the debugger calls Read(), which will try to go to the next row. Does your table only have 1 row?
The first time you view the data (when you can actually see it, not the second time when you get the Exception), are there multiple rows shown? If not, then you have an issue with your query as it is only returning one row.
If there are multiple rows, there may be an issue with using LINQ on a DataReader object. Full transparency, I haven't used LINQ to loop through a SqlDataReader before. This is how I would do it:
using (var rdr = cmd.ExectuteReader())
{
while(rdr.Read())
{
//do something with the first column
Console.WriteLine(rdr[0]);
}
}
If you want to use LINQ, you could always create a datatable to read from.
using (var rdr = cmd.ExectuteReader())
{
DataTable datatable = new DataTable();
datatable.Load(rdr)
}
...
var results = (from row in datatable...

The first time it works displaying a subset of your data. At the index of last successful row + 1 there might be a breaking record.
Then the enumerator will stop working.
In my specific case, calling the ToList() worked fine. (CsvHelper, CS0726)
https://github.com/JoshClose/CsvHelper/issues/1434

Getting Database values into variable form c#

I am developing a cricket simulation and i need to retrieve certain statistics from a players data. I've got the following code.
public List<float> BattingData()
{
con.ConnectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString.ToString();
string query = "SELECT [INNS], [NOT OUTS], [AVG] FROM [" + batTeam + "] WHERE [Player] = '" + name + "';";
SqlCommand com = new SqlCommand(query, con);
con.Open();
using (SqlDataReader reader = com.ExecuteReader())
{
if(reader.HasRows)
{
while (reader.NextResult())
{
Innings = Convert.ToInt32(reader["INNS"]);
NotOuts = Convert.ToInt32(reader["NOT OUTS"]);
Avg = Convert.ToSingle(reader["AVG"]);
}
}
}
con.Close();
OutRatePG = (Innings = NotOuts) / Innings;
OutRatePB = OutRatePG / 240;
RunsPB = Avg / 240;
battingData.Add(OutRatePB);
battingData.Add(RunsPB);
return battingData;
}
The error that I am getting is that when I try to divie by 'Innings' it is saying cannot divide by zero, so I think the variables are being returned as zero and no data is being assigned to them.

This line is the issue:
while (reader.NextResult())
What this does is move the reader to the next resultset, ignoring the rest of the rows unread. To advance a reader to the next row, you need to call reader.Read() instead.
You have some other issues with your code:
You appear to have a separate table for each team. This is incorrect database design. You should create a Team table, with each team in it, and then foreign key your TeamResults table to it. Query it using INNER JOIN.
You are concatenating user-entered values to your query. This leaves you open to SQL injection attacks. Use parameters instead. (You cannot parameterize a table name, another reason you should do as above 1.)
You do not need to check for HasRows. If there are no rows, Read() will return false.
It looks like you only want one row. If that is the case you don't want a while(reader.Read()) loop, instead if(reader.Read()). (If you only need a single value, you can refactor the code to use command.ExecuteScalar().)

In database records check if value for Innings has 0
also you can try the below code before performing any operation.
> if(Innings>0) { OutRatePG = (Innings - NotOuts) / Innings; }

Read records from one table , and write to another table. Exception occurs procedure or function has too many arguments specified?

I am trying to retrieve list of records from one table , and write to another table. I've used a simple query to retrieve the values to SqlDataReader,then load them to a DataTable. Using the DataTableReader , I am going through the entire data set which is Saved in DataTable. The problem is, while reading each and every record I am trying to insert those values to another table using a Stored Procedure.But it only insert the first row of values,and for the second row onward giving some Exception saying."procedure or function has too many arguments specified".
string ConStr = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
SqlConnection NewCon = new SqlConnection(ConStr);
NewCon.Open();
SqlCommand NewCmd3 = NewCon.CreateCommand();
NewCmd3.CommandType = CommandType.Text;
NewCmd3.CommandText ="select * from dbo.Request_List where group_no ='" +group_no+ "'";
NewCon.Close();
NewCon.Open();
SqlDataReader dr = (SqlDataReader)NewCmd3.ExecuteReader();
DataTable dt = new DataTable();
dt.Load(dr);
DataTableReader reader = new DataTableReader(dt);
NewCmd.Dispose();
NewCon.Close();
NewCon.Open();
SqlCommand NewCmdGrpReqSer = NewCon.CreateCommand();
NewCmdGrpReqSer.CommandType = CommandType.StoredProcedure;
NewCmdGrpReqSer.CommandText = "Voucher_Request_Connection";
if (reader.HasRows)
{
int request_no = 0;
while (reader.Read())
{
request_no = (int)reader["request_no"];
NewCmdGrpReqSer.Parameters.Add("#serial_no", serial_no);
NewCmdGrpReqSer.Parameters.Add("#request_no", request_no);
try
{
NewCmdGrpReqSer.ExecuteNonQuery();
MessageBox.Show("Connection Updated");//just to check the status.tempory
}
catch (Exception xcep)
{
MessageBox.Show(xcep.Message);
}
MessageBox.Show(request_no.ToString());//
}
NewCmdGrpReqSer.Dispose();
NewCon.Close();
}
Any Solutions ?

As #Sparky suggests, the problem is that you continue to add parameters to the insertion command. There are several other ways in which the code could be improved, however. These improvements would remove the need to clear the parameters and would help to make sure you don't leave disposable resources undisposed.
First - use the using statement for your disposable objects. This removes the need for the explicit Close (btw, only one of Close/Dispose is needed for the connection as I believe Dispose calls Close). Second, simply create a new command for each insertion. This will prevent complex logic around resetting the parameters and, possibly, handling error states for the command. Third, check the results of the insertion to make sure it succeeds. Fourth, explicitly catch a SqlException - you don't want to accidentally hide unexpected errors in your code. If it's necessary to make sure all exceptions don't bubble up, consider using multiple exception handlers and "doing the right thing" for each case - say logging with different error levels or categories, aborting the entire operation rather than just this insert, etc. Lastly, I would use better variable names. In particular, avoid appending numeric identifiers to generic variable names. This makes the code harder to understand, both for others and for yourself after you've let the code sit for awhile.
Here's my version. Note there are several other things that I might do such as make the string literals into appropriately named constants. Introduce a strongly-typed wrapper around the ConfigurationManager object to make testing easier. Remove the underscores from the variable names and use camelCase instead. Though those are more stylistic in nature, you might want to consider them as well.
var connectionString = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
using (var newConnection = new SqlConnection(connectionString))
{
newConnection.Open();
using (var selectCommand = newConnection.CreateCommand())
{
selectCommand.CommandType = CommandType.Text;
select.CommandText ="select request_no from dbo.Request_List where group_no = #groupNumber";
selectCommand.Parameters.AddWithValue("groupNumber", group_no);
using (dataReader = (SqlDataReader)newCommand.ExecuteReader())
{
while (reader.HasRows && reader.Read())
{
using (var insertCommand = newConnection.CreateCommand())
{
insertCommand.CommandType = CommandType.StoredProcedure;
insertCommand.CommandText = "Voucher_Request_Connection";
var request_no = (int)reader["request_no"];
insertCommand.Parameters.Add("#serial_no", serial_no);
insertCommand.Parameters.Add("#request_no", request_no);
try
{
if (insertCommand.ExecuteNonQuery() == 1)
{
MessageBox.Show("Connection Updated");//just to check the status.tempory
}
else
{
MessageBox.Show("Connection was not updated " + request_no);
}
}
catch (SqlException xcep)
{
MessageBox.Show(xcep.Message);
}
MessageBox.Show(request_no.ToString());//
}
}
}
}
}

Try clearing your parameters each time...
while (reader.Read())
{
request_no = (int)reader["request_no"];
// Add this line
NewCmdGrpReqSer.Parameters.Clear();
NewCmdGrpReqSer.Parameters.Add("#serial_no", serial_no);
NewCmdGrpReqSer.Parameters.Add("#request_no", request_no);
try
{

Best way to move data between tables in MYSQL

I have a question regarding performance. This is my scenario.
I have a MYSQL database and a application that from time to time moves records, according to the criteria from a query, from one table to another. The way this is done is:
foreach(object obj in list)
{
string id = obj.ToString().Split(',')[0].Trim();
string query = " insert into old_records select * from testes where id='" +
id + "';" + " delete from testes where id='" + id +"'";
DB _db = new DB();
_db.DBConnect(query);
this is the way I connect to the database:
DataTable _dt = new DataTable();
MySqlConnection _conn = new MySqlConnection(connectionString);
MySqlCommand _cmd = new MySqlCommand
{
Connection = _conn,
CommandText = query
};
MySqlDataAdapter _da = new MySqlDataAdapter(_cmd);
MySqlCommandBuilder _cb = new MySqlCommandBuilder(_da);
_dt.Clear();
try
{
_conn.Open();
_cmd.ExecuteNonQuery();
_da.Fill(_dt);
}
catch (MySqlException ex)
{
Console.WriteLine(ex.Message);
}
finally
{
if (_conn != null) _conn.Close();
}
return _dt;
So my question is, I have like 4000 rows in the table, and it takes a lot of time to move all the records from one table to another, specially across a network. Is there a way to make this faster?
I have been doing some reading and there are several option to handle data from DB like data adapters, reader, set, and tables. Which one is faster for this case? Should I be using a different method?

Two things I see is that first you're opening and closing your connection for each insert, that's usually your most expensive operation so you won't want to do that. You can also try batching them rather than doing them at once. When you do that you have to be careful because things could break in the middle of a large update so you would want to do things in a transaction. Without knowing too much about what your data structure looks like I refactored your method to do batching 100 at a time. First create a little helper method called move items that takes a connection and a list of ids. Don't do a try catch in this, you'll see why later.
Note: This method doesn't use parameters, I highly recommend you change it to do that.
private static void MoveItems(MySqlConnection conn, List<string> moveList)
{
string query = string.Format("insert into old_records select * from testes where id IN({0});" + " delete from testes where id IN({0})", string.Join(",", moveList.ToArray()));
var cmd = new MySqlCommand
{
Connection = conn,
CommandText = query
};
cmd.ExecuteNonQuery();
}
Next you'll change your main method to open the database connection once and then call this method 100 id's at a time. This method will have a try catch therefore if the call to MoveItems throws an exception it will be caught in this main method.
// the using statement will call your dispose method
using (var conn = new MySqlConnection(connectionString))
{
// open the connection and start the transaction
conn.Open();
var transaction = conn.BeginTransaction();
// createa list to temporarily store the ids
List<string> moves = new List<string>();
try
{
// clean the list, do the trim and get everything that's not null or empty
var cleanList = list.Select(obj => obj.ToString().Split(',')[0].Trim()).Where(s => !string.IsNullOrEmpty(s));
// loop over the clean list
foreach (string id in cleanList)
{
// add the id to the move list
moves.Add("'" + id + "'");
// batch 100 at a time
if (moves.Count % 100 == 0)
{
// when I reach 100 execute them and clear the list out
MoveItems(conn, moves);
moves.Clear();
}
}
// The list count might not be n (mod 100) therefore see if there's anything left
if (moves.Count > 0)
{
MoveItems(conn, moves);
moves.Clear();
}
// wohoo! commit the transaction
transaction.Commit();
}
catch (MySqlException ex)
{
// oops! something happened roll back everything
transaction.Rollback();
Console.WriteLine(ex.Message);
}
finally
{
conn.Close();
}
}
You may have to play with that 100 number. I remember when I worked with MySQL a lot I saw some performance differences between doing an IN and giving it a list of Or statements (Id = 'ID1' OR id = 'ID2' ...). But executing 40 statements or 80 statements will certainly have better performance, and opening the database connection once instead of 4000 times should also give you much better performance.

I might be wrong, but there is not much you can do in order to make it faster. After all you want to get the entire table data and insert its information into another table. The process will take some time if your table isn't small. However, you can try using the code below. It should do the trick and save some time.
INSERT INTO TABLE2 (FIELDNAME_IN_TABLE2, FIELDNAME2_IN_TABLE2)
SELECT FIELDNAME_IN_TABLE1, FIELDNAME2_IN_TABLE1
FROM TABLE1

Why code is maxing out the CPU while querying the database?

My C# code below checks a SQL database to see if a record matches a ClientID and a User Name. If more than 15 or more matching records are found that match, the CPU on my Windows 2008 server peaks at about 78% while the 15 records are found while the below C# code executes. The SQL Server 2008 database and software is located on another server so the problem is not with SQL Server spiking the CPU. The problem is with my C# software that is executing the code below. I can see my software executable that contains the C# code below spike to 78% while the database query is executed and the records are found.
Can someone please tell me if there is something wrong with my code that is causing the CPU to spike when 15 or more matching records are found? Can you also please tell/show me how to optimize my code?
Update: If it finds 10 records, the CPU only spikes at 2-3 percent. It is only when it finds 15 or more records does the CPU spike at 78% for two to three seconds.
//ClientID[0] will contain a ClientID of 10 characters
//output[0] will contain a User Name
char[] trimChars = { ' ' };
using (var connection = new SqlConnection(string.Format(GlobalClass.SQLConnectionString, "History")))
{
connection.Open();
using (var command = new SqlCommand())
{
command.CommandText = string.Format(#"SELECT Count(*) FROM Filelist WHERE [ToAccountName] = '" + output[0] + #"'");
command.Connection = connection;
var rows = (int) command.ExecuteScalar();
if (rows >= 0)
{
command.CommandText = string.Format(#"SELECT * FROM Filelist WHERE [ToAccountName] = '" + output[0] + #"'");
using (SqlDataReader reader = command.ExecuteReader())
{
if (reader.HasRows)
{
while (reader.Read())
{
//Make sure ClientID does NOT exist in the ClientID field
if (reader["ClientID"].ToString().TrimEnd(trimChars).IndexOf(ClientID[0]) !=
-1)
{
//If we are here, then do something
}
}
}
reader.Close();
reader.Dispose();
}
}
// Close the connection
if (connection != null)
{
connection.Close();
}
}
}

You can decrease the number of database access from 2 to 1 if will remove first query, it is not necessary.
using (SqlConnection connection = new SqlConnection(connectionString))
using (SqlCommand command = connection.CreateCommand())
{
command.CommandText = "SELECT ClientID FROM dbo.Filelist WHERE ToAccountName = #param"; // note single column in select clause
command.Parameters.AddWithValue("#param", output[0]); // note parameterized query
connection.Open();
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read()) // reader.HasRow is doubtfully necessary
{
// logic goes here
// but it's better to perform it on data layer too
// or return all clients first, then perform client-side logic
yield return reader.GetString(0);
}
} // note that using block calls Dispose()/Close() automatically
}

Change this:
SELECT * FROM Filelist
To this:
SELECT ClientID FROM Filelist
And check for performance.
I suspect there is a blob field on your select.
Also select * is not recommended, write your exact interested fields in your query.

Nothing looks obviously CPU intensive, but one problem does stand out.
You are running a query to count how many records there are
"SELECT Count(*) FROM Filelist WHERE [ToAccountName] = '" + output[0] + #"'"
Then, if more than 0 is returned, you are running another query to get the data.
"SELECT * FROM Filelist WHERE [ToAccountName] = '" + output[0] + #"'"
This is redundant. Get rid of the first query, and just use the second one, checking to see if the reader has data. You can also get rid of the HasRows call and just do
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
}
}

Please consider what already said about parametrized queries.
Beside that, I think that the only big issue could arise in the following block:
while (reader.Read())
{
//Make sure ClientID does NOT exist in the ClientID field
if (reader["ClientID"].ToString().TrimEnd(trimChars).IndexOf(ClientID[0]) != -1)
{
//If we are here, then do something
}
}
So try to just cache your reader.Read() data in some local variable, releasing the SQL resources asap, then you can work on the data you just retrieved. Eg:
List<string> myRows = new List<string>();
while (reader.Read())
{
myRows.Add(reader["ClientID"].ToString();
}
/// quit the using clause
/// now elaborate what you got in myRows

There is nothing in the code to indicate a performance problem.
What does SQL Profiler show?
(Both in terms of query plan, and server resources used.)
Edit: To make this clearer: you have one measurement that might indicate an issue. You now need to measure more deeply to understand if it really is a problem, only you can do this (no one else has access to the hardware).

I strongly recommend that you get a copy of dotTrace from JetBrains.
At the very least, profiling the client code will help you identify/eliminate the source of the CPU spike.

I recommend using parameters as suggested, however, I have seen performance problems where the type of the string column does not match the C# string. In these cases, I suggest specifying the type explicitly.
Like this:
command.CommandText = "SELECT ClientID FROM dbo.Filelist WHERE ToAccountName = #accountName";
command.Parameters.Add("#accountName", SqlDbType.NVarChar, 16, output[0]);
Or this:
SqlParameter param = command.Parameters.Add(
"#accountName", SqlDbType.NVarChar);
param.Size = 16; //optional
param.Value = output[0];