In my C# application I am trying to read data within my Accounts table, read the data as a decimal, preform a a calculation on it, and then update the same row.
Right now it reads the correct data in the column but two things go wrong when trying to update.
It sets all of the data in the AccountTotal column to the same value. This value is correct for the first row, but incorrect for the rest.
I believe the second problems occurs in calculating the data that is to be updated. When I try to update the DB, it sets the value twice as high as I am wanting it to be. For example: In my CalculateIncome method I wan't to add 100 to the account total, It adds 200.
What is causing these two problems?
Here is the program:
class Program
{
static void Main(string[] args)
{
//Need to change when deploying on real database.
const string DB_NAME = "Bank.sdf";
const string DB_PATH = #"C:\Users\Lucas\eBankRepository\eBank\App_Data\" + DB_NAME; // Use ".\" for CWD or a specific path
const string CONNECTION_STRING = "Data Source=" + DB_PATH;
decimal AccountTotal;
var conn = new SqlCeConnection(CONNECTION_STRING);
SqlCeDataReader reader = null;
try
{
conn.Open();
//Basic Query of all accounts
SqlCeCommand Query = new SqlCeCommand("SELECT * FROM Accounts", conn);
reader = Query.ExecuteReader();
while (reader.Read())
{
AccountTotal = reader.GetDecimal(2); //Column in DB for Account Total
AccountTotal += CalculateIncome();
//Update Total
SqlCeCommand UpdateTotal = new SqlCeCommand("UPDATE Accounts SET AccountTotal = #UpdatedTotal", conn); // Error when using WHERE Clause "WHERE AccountName= # Savings"
UpdateTotal.Parameters.AddWithValue("#UpdatedTotal", AccountTotal);
UpdateTotal.Connection = conn;
UpdateTotal.ExecuteNonQuery();
}
}
finally
{
if (reader != null)
{
reader.Close();
}
if (conn != null)
{
conn.Close();
}
}
}
public static decimal CalculateIncome()
{
return 100;
}
}
EDIT:
Here is the code I had before that included the WHERE clause in the command. With this code, it now only updates the the rows where it has an account name of "Savings," but it still sets the value in each of the rows to be the same for AccountTotal
while (reader.Read())
{
AccountTotal = reader.GetDecimal(2); //Column in DB for Account Total
AccountTotal += CalculateIncome();
//Update Total
SqlCeCommand UpdateTotal = new SqlCeCommand("UPDATE Accounts SET AccountTotal = #UpdatedTotal WHERE AccountName= #Savings", conn); // Error when using WHERE Clause "WHERE AccountName= # avings"
UpdateTotal.Parameters.AddWithValue("#UpdatedTotal", AccountTotal);
UpdateTotal.Parameters.AddWithValue("#Savings", "Savings");
UpdateTotal.Connection = conn;
UpdateTotal.ExecuteNonQuery();
}
Here is a visual as well for before and after the program is being run.
Before
After
Working Code
while (reader.Read())
{
AccountTotal = reader.GetDecimal(2); //Column in DB for Account Total
//Console.WriteLine(AccountTotal);
AccountTotal += CalculateIncome();
//Console.WriteLine(AccountTotal);
//Update Total
SqlCeCommand UpdateTotal = new SqlCeCommand("UPDATE Accounts SET AccountTotal = #UpdatedTotal WHERE AccountName = #Savings AND AccountID = #ID", conn);
UpdateTotal.Parameters.AddWithValue("#UpdatedTotal", AccountTotal);
UpdateTotal.Parameters.AddWithValue("#Savings", "Savings");
UpdateTotal.Parameters.AddWithValue("#ID", reader.GetInt32(0));
UpdateTotal.Connection = conn;
UpdateTotal.ExecuteNonQuery();
AccountTotal = 0; //Reset
}
Your two issues are:
It's updating all the rows to be the same value
This is because there isn't a where clause in your update statement.
It's making the value double up.
This is because of the line AccountTotal += CalculateIncome();
What this does is in the first run make it be 100 and the second loop around it makes it be 200.
Related
So I am trying to use two different inputs from a user to get two different values then multiply them together to get an answer.
//code to get value
SqlCommand cmd = new SqlCommand("select Charges, Students from Subs where Subject_name='" + Subject + "'and Level='" + Level + "'", con);
//code to read and times the values
var reader = cmd.ExecuteReader();
int Price = Convert.ToInt32(reader["Charges"]);
int NumS = Convert.ToInt32(reader["Subject_name"]);
int final = (Price*NumS) / 100;
status = final + "$";
You should try something like this:
// Define **parametrized** query
string query = "SELECT Charges, Students FROM dbo.Subs WHERE Subject_name = #SubjectName AND Level = #Level;";
using (SqlCommand cmd = new SqlCommand(query, con))
{
// define the parameters and set value
// I'm just *guessing* what datatype and what length these parameters are - please adapt as needed !
cmd.Parameters.Add("#SubjectName", SqlDbType.VarChar, 50).Value = Subject;
cmd.Parameters.Add("#Level", SqlDbType.Int).Value = Level;
SqlDataReader reader = cmd.ExecuteReader();
while (reader.Read())
{
int Price = reader.GetInt32(0); // index = 0 is "Charges" of type INT
// you are **NOT** selecting "Subject_Name" in your query - you therefore **CANNOT** read it from the SqlDataReader
// int NumS = Convert.ToInt32(reader["Subject_name"]);
int NumS = 1.0;
int final = (Price * NumS) / 100;
status = final + "$";
}
}
Points to ponder:
You should also put your SqlConnection con into a proper using (..) { ... } block to ensure disposal
You need to check the parameters - since you hadn't specified anything in your question, and also not posted any information about them, I can only guess
Be aware - the SqlDataReader might (and in a great many cases will) return multiple rows - which you need to iterate over
If you want to read out a column from the database table - it must be in the SELECT list of columns! You're trying to read out a column you're not selecting - that won't work, of course. ...
I have been working on a personal project for the company I work for to control stock levels in order to practice my c#.
I want my application to search through tblJuiceStock, find a matching FlavourID to what the user is inputting and update the stock of that record through an UPDATE SET query.
public void InsertJuiceStockWithCheck()
{
using (OleDbConnection conn = new OleDbConnection())
{
conn.ConnectionString = ConnectionString;
conn.Open();
string tblJuiceStockCheck = "SELECT FlavourID, Quantity FROM tblJuiceStock";
OleDbCommand cmdCheck = new OleDbCommand(tblJuiceStockCheck, conn);
OleDbDataAdapter daCheck = new OleDbDataAdapter(cmdCheck);
DataTable dtCheck = new DataTable();
daCheck.Fill(dtCheck);
foreach (DataRow row in dtCheck.Rows)
{
if ((int)row["FlavourID"] == fID)
{
int currentQty = (int)row["Quantity"];
int updatedQty = currentQty + qty;
string tblJuiceStockExisting = #"UPDATE tblJuiceStock
SET Quantity = #newquantity
WHERE FlavourID = #flavourID";
OleDbCommand cmdJuiceStockExisting = new OleDbCommand(tblJuiceStockExisting, conn);
cmdJuiceStockExisting.Parameters.AddWithValue("#flavourID", fID);
cmdJuiceStockExisting.Parameters.AddWithValue("#newquantity", updatedQty);
cmdJuiceStockExisting.ExecuteNonQuery();
matchFound = true;
break;
}
}
if (!matchFound)
{
string tblJuiceStockNew = "INSERT INTO tblJuiceStock (FlavourID, Quantity, MinStockPOS) VALUES (#fID, #quantity, #minstock)";
OleDbCommand cmdJuiceStockNew = new OleDbCommand(tblJuiceStockNew, conn);
cmdJuiceStockNew.Parameters.AddWithValue("#fID", fID);
cmdJuiceStockNew.Parameters.AddWithValue("#quantity", qty);
cmdJuiceStockNew.Parameters.AddWithValue("#minstock", amt);
cmdJuiceStockNew.ExecuteNonQuery();
}
}
}
Please note: this query works fine in Access when I replace parameters with the same values. Also, using breakpoints I identified that the parameters have the correct values set to them, the variables assigned to them are obtained within another method, all methods are called in the submit button event.
However, the Quantity value in TblJuiceStock remains the same.
My tblJuiceStock table
After some time of messing about the answer was simple.
OLEDB does work with named parameters but you have to declare them, if you don't declare them they use the parameters positioning to match them up.
My problem was that in my query string I had #newquantity first and #flavourID second, whereas when adding my parameters I added #flavourID first and #newquantity second.
New to stackoverflow and very much a c# beginner
Currently creating a form which produces a bar chart from data stored in a database. The chosen record is identified by pID (patient's ID) and tdate (Test date). These values are determined by 2 combo boxes that the user can select from, The problem I am having is that only the first and last records stored in the database are populating the barchart.
if (radioButtonTestResult.Checked)
{
foreach (var series in TestResultBarChart.Series)
{
series.Points.Clear();
}
string tdate = comboBox2.Text;
using (SqlConnection connection = new SqlConnection(#"Data Source= (LocalDB)\v11.0;AttachDbFilename=|DataDirectory|\MMSEDB.mdf;Integrated Security=True"))
{
connection.Open();
string sql = "SELECT T_CLOCK_SCORE,T_LANGUAGE_SCORE,T_RECALL_SCORE,T_REGISTRATION_SCORE,T_ORIENTATION _SCORE,T_TIME FROM TEST_RESULTS WHERE P_ID='" + pID + "' AND T_DATE='"+ tdate +"'";
using(SqlCommand command = new SqlCommand(sql, connection))
{
command.CommandTimeout = 3600;
using (SqlDataReader reader = command.ExecuteReader(CommandBehavior.SequentialAccess))
{
while (reader.Read())
{
MessageBox.Show("hello4");
String clockScoreString = reader["T_CLOCK_SCORE"].ToString();
MessageBox.Show(clockScoreString);
clockScore = Int32.Parse(clockScoreString);
String langScoreString = reader["T_LANGUAGE_SCORE"].ToString();
langScore = Int32.Parse(langScoreString);
String recallScoreString = reader["T_RECALL_SCORE"].ToString();
recallScore = Int32.Parse(recallScoreString);
String regScoreString = reader["T_REGISTRATION_SCORE"].ToString();
regScore = Int32.Parse(regScoreString);
String orientScoreString = reader["T_ORIENTATION_SCORE"].ToString();
orientScore = Int32.Parse(orientScoreString);
String timeScoreString = reader["T_TIME"].ToString();
timeScore = Int32.Parse(timeScoreString);
}
reader.Close();
}
}
this.TestResultBarChart.Series["Series1"].Points.AddXY("Clock Score", clockScore);
this.TestResultBarChart.Series["Series1"].Points.AddXY("Language Score", langScore);
this.TestResultBarChart.Series["Series1"].Points.AddXY("Recall Score", recallScore);
this.TestResultBarChart.Series["Series1"].Points.AddXY("Registration Score", regScore);
this.TestResultBarChart.Series["Series1"].Points.AddXY("Orientation Score", orientScore);
}
}
Here is a pic of the data:
Test_results_table
here is a pic of the interface with the first record working:
interface
I know this has something to do with the reader but can't work out how to get to function correctly
Any help is very much appreciated
You are reading in a loop all the returned values, then exit from the loop and use just the last value to set your Points. You should move the Point settings inside the loop
....
while (reader.Read())
{
clockScore = Convert.ToInt32(reader["T_CLOCK_SCORE"]);
langScore = Convert.ToInt32(reader["T_LANGUAGE_SCORE"]);
recallScore = Convert.ToInt32(reader["T_RECALL_SCORE"]);
regScore = Convert.ToInt32(reader["T_REGISTRATION_SCORE"]);
orientScore = Convert.ToInt32(reader["T_ORIENTATION_SCORE"]);
timeScore = Convert.ToInt32(reader["T_TIME"]);
this.TestResultBarChart.Series["Series1"].Points.AddXY("Clock Score", clockScore);
this.TestResultBarChart.Series["Series1"].Points.AddXY("Language Score", langScore);
this.TestResultBarChart.Series["Series1"].Points.AddXY("Recall Score", recallScore);
this.TestResultBarChart.Series["Series1"].Points.AddXY("Registration Score", regScore);
this.TestResultBarChart.Series["Series1"].Points.AddXY("Orientation Score", orientScore);
}
reader.Close();
Note that your query is built using string concatenation. This is a well known problem with database code. Never do it and use a parameterized query
EDIT
Looking at your comment below, I repeat the advice to use a parameterized query instead of string concatenation. Not only this avoid Sql Injection hacks but also you don't leave the job to understand the meaning of your values to the database engine
DateTime tDate = Convert.ToDateTime(comboBox2.Text);
......
string sql = #"SELECT
T_CLOCK_SCORE,T_LANGUAGE_SCORE,T_RECALL_SCORE,
T_REGISTRATION_SCORE,T_ORIENTATION_SCORE,T_TIME
FROM TEST_RESULTS
WHERE P_ID=#id AND T_DATE=#date";
using(SqlCommand command = new SqlCommand(sql, connection))
{
command.Parameters.Add("#id", SqlDbType.Int).Value = pID;
command.Parameters.Add("#date", SqlDbType.Date).Value = tdate;
command.CommandTimeout = 3600;
using (SqlDataReader reader = command.ExecuteReader(CommandBehavior.SequentialAccess))
{
while (reader.Read())
....
In this example I assume that the variable pID is of type integer and the variable tDate is of type DateTime matching the type of the database fields. This doesn't leave any doubt to the database engine on your values.
Of course if the fields are of different type then you should change the SqlDbType accordingly.
I have a simple database that I am using. It contains two entries for users which is a user with UserID 1 and IsAdmin 0 and another with UserID 3041234567 and IsAdmin of 1. The only fields in the database is a string UserID and a bit IsAdmin. I am reading from the database with the following code:
SqlConnection conn = new SqlConnection(Properties.Settings.Default.Conn);
conn.Open();
SqlCommand cmd = new SqlCommand("SELECT * FROM Users WHERE UserID = " + t.Text.ToString(), conn);
SqlDataReader reader = cmd.ExecuteReader();
if (reader.HasRows)
{
while (reader.Read())
{
user.UserID = reader["UserID"].ToString();
user.IsAdmin = Convert.ToBoolean(reader["IsAdmin"]);
}
}
conn.Close();
If I enter the number 3041234567 as the UserID everything works perfectly, but If I enter the number 1 I get an exception saying that "The conversion of the nvarchar value '3041234567' overflowed an int column."
If I set a breakpoint and watch the while(reader.read()) loop the loop iterates through fine and sets the user.UserID = 1 and the user.IsAdmin = false. The exception is thrown when the loop begins to iterate a second time. I guess I have a couple of questions:
Why is the loop iterating a second time?
How is the ID 3041234567 being returned with the sql command "SELECT * FROM Users WHERE UserID = 1"
What is the int column that is being overflowed?
Well, since
3041234567 > int.MaxValue ( == 2147483647)
you've got an overflow; if you want some kind of integer value, however, try long (which is 64 bit long):
long value = Convert.ToInt64(reader["UserID"]);
Something like this:
// Wrap IDisposable into using
using (SqlConnection conn = new SqlConnection(Properties.Settings.Default.Conn)) {
conn.Open();
// Make sql
// 1. Readable
// 2. Parametrized
// 3. Avoid * in select
String sql =
#"select UserID,
IsAdmin
from Users
where UserID = #prm_UserId";
// Wrap IDisposable into using
using (SqlCommand cmd = new SqlCommand(sql, conn)) {
// Explicit data type will be better here (Add Parameter with type)
// but I don't know it
cmd.Parameters.AddWidthValue("prm_UserId", t.Text);
// Wrap IDisposable into using
using (SqlDataReader reader = cmd.ExecuteReader()) {
// You don't want to iterate the whole cursor, but the first record
if (reader.Read()) {
//TODO: Make UserID being "long"
user.UserID = Convert.ToInt64(reader["UserID"]);
user.IsAdmin = Convert.ToBoolean(reader["IsAdmin"]);
}
}
}
}
I am currently working on an C# project and I am trying to get the number of rows returned from MySQL Data Reader.
I know there is no direct function so I am trying to write my own. In the function, I pass it the MySQLDataReader object and then loop through the MySQL Data Reader and increment a counter and return the value of the counter.
This then seems to lock up the program, I guess because I am Reader.read() after I've got the count I'm already at the end. Instead I have tried creating a copy of the reader and then loop through the temp version but I get the same result.
Below is my code where I am executing the query and calling the function.
string query = "SELECT * FROM reports, software, platforms, versions "
+ "WHERE EmailVerified = #verified AND reports.SoftwareID = software.id AND reports.PlatformID = platforms.id "
+ "AND reports.VersionID = versions.id AND BugReportAcceptedNotificationSent = #notificationSent";
using (MySqlCommand cmd = new MySqlCommand(query, db.conn))
{
cmd.Parameters.AddWithValue("#verified", "1");
cmd.Parameters.AddWithValue("#notificationSent", "0");
using (MySqlDataReader reader = cmd.ExecuteReader())
{
totalEmails = HelperClass.totalRowsInMySQLDataReader(reader);
while (reader.Read())
{
currentEmailCount++;
EmailNotifications emailNotification = new EmailNotifications(reader);
emailNotification.sendNewBugReportAfterVerificationEmail(currentEmailCount, totalEmails);
}
}
}
Below is my function that gets the row count
public static int totalRowsInMySQLDataReader(MySqlDataReader reader)
{
MySqlDataReader tempReader = reader;
ILibraryInterface library = GeneralTasks.returnBitsLibrary(Configuration.databaseSettings, Configuration.engineConfig.logFile);
string methodInfo = classDetails + MethodInfo.GetCurrentMethod().Name;
try
{
int count = 0;
while (tempReader.Read())
{
count++;
}
tempReader = null;
return count;
}
catch (Exception ex)
{
string error = string.Format("Failed to get total rows in MySQL Database. Exception: {0}", ex.Message);
library.logging(methodInfo, error);
library.setAlarm(error, CommonTasks.AlarmStatus.Medium, methodInfo);
return -1;
}
}
Make use of a DataTable to load your results, e.g.
DataTable dt = new DataTable();
dt.Load(reader);
int numberOfResults = dt.Rows.Count;
You can then also iterate over the rows to read the values, e.g.
foreach(DataRow dr in dt.Rows)
{
var value = dr["SomeResultingColumn"]
}
The other option is to issue two separate SQL statements, however you would need to ensure both statements were enclosed within a transaction with a Serializable isolation level, this is needed to make sure records aren't inserted between the execution of the two SQL statements.
To avoid multiple queries, how about including the total in the select itself?
SELECT COUNT(*) AS TotalNORows, * FROM reports, software, platforms, versions etc
i think without executing another command it's not possible...as there is no method available for count in reader class
you can try this... if it works..
string query = "SELECT * FROM reports, software, platforms, versions "
+ "WHERE EmailVerified=#verified AND reports.SoftwareID=software.id AND reports.PlatformID=platforms.id "
+ "AND reports.VersionID=versions.id AND BugReportAcceptedNotificationSent=#notificationSent";
using (MySqlCommand cmd = new MySqlCommand(query, db.conn))
{
cmd.Parameters.AddWithValue("#verified", "1");
cmd.Parameters.AddWithValue("#notificationSent", "0");
using (MySqlDataReader reader = cmd.ExecuteReader())
{
// create a new connection db.conn2 then
MySqlCommand cmd2 = new MySqlCommand(query, db.conn2))
cmd2.Parameters.AddWithValue("#verified", "1");
cmd2.Parameters.AddWithValue("#notificationSent", "0");
MySqlDataReader reader2 = cmd2.ExecuteReader();
int numberofrow=0;
while(reader2.Read())
numberofrow++;
//your codes......
}
Was working on the same problem. I hate having to iterate if a method is already available, but this is was the shortest bit I could come up with:
MySqlCommand cmd = new MySqlCommand(query, connection);
MySqlDataReader reader = cmd.ExecuteReader();
int rowcount = 0;
while(reader.Read()){
rowcount++;
}
First, create this class:
public static class Extensions
{
public static int Count(this MySqlDataReader dr)
{
int count = 0;
while(dr.Read())
count++;
return count;
}
}
This will implement .Count () on MySqlDataReader.
int count = reader.Count();
Exemple:
string sql= "SELECT * FROM TABLE";
MySqlCommand cmd = new MySqlCommand(sql, connection);
MySqlDataReader reader = cmd.ExecuteReader();
int count = reader.Count();
Maybe you could look things the other way around
You could just do a select count(*) and get the row count
or
use a data adapter to fill a container (like a DataTable) and count the rows
Unfortunatelly solution from Jan Van #Herck will return one row only, so in case you are interested in getting all rows and their number in one select, this isn't what you need.
In that case I suggest uou to try this:
select * , (select count(*) from my_table) AS numRow from my_table;
or read this:
Getting total mysql results returned from query with a limit: FOUND_ROWS error
You can use follwoing SQL Query to get the total rows Count.
SELECT COUNT(*) FROM [MYTABLE]
from the Code you can use ExecuteScalar() method to get the total number of rows returned by QUERY.
Try This:
int GetRowsCount(MySqlCommand command)
{
int rowsCount=Convert.ToIn32(command.ExecuteScalar());
return rowsCount;
}
Use above function as below:
MySqlCommand command=new MySlCommand("Select count(*) from MyTable",connectionObj);
int totalRows = GetRowsCount(command)
OleDbDataReader dbreader = new OleDbDataReader();
int intcount = 0;
if (dbreader.HasRows == true)
{
if (dbreader.Read())
{
intcount = dbreader.RecordsAffected;
}
}
"dbreader.RecordsAffected" will give you the number rows changed,inserted or deleted by the last statement of SQL