I have searched for my answer only to find that there was a typo in someone's code.
I have not found why this code does not have a definition for ExecuteScalar(). I might actually need to capture Customer_Id when I actually add the row to the SQL database because it is auto increment.
Here is my code that had the problem:
if (customer_IDTextBox == null)
{
sqlConnection.Open();
string SQL = "SELECT MAX(Customer_ID) FROM Customer";
int maxId = Convert.ToInt32(SQL.ExecuteScalar());
sqlConnection.Close();
}
You need to create an instance of SqlCommand, then assign your connection and query to it.
Try this code instead. (A couple bits of advice. I've surrounded your connection and command in using statements so there's no need to close anything... they'll be disposed of. Also, always try to create connections and commands as close as possible to the point where you're going to need them.)
int maxId = -1;
if (customer_IDTextBox == null)
{
using (var sqlConnection = new SqlConnection(/* your connection string */))
{
sqlConnection.Open();
string query = "SELECT MAX(Customer_ID) FROM Customer";
using (var sqlCommand = new SqlCommand(query, sqlConnection))
{
maxId = Convert.ToInt32(sqlCommand.ExecuteScalar());
}
}
}
Related
Is there anything wrong with my codes? Because, I'm about to create a login form and it doesn't.
OleDbConnection conDataBase = new OleDbConnection(#"Provider=Microsoft.ACE.OLEDB.12.0; Data Source = C:\Users\tess\Documents\iknow.accdb;" + "Persist Security Info = True");
OleDbCommand cmdDataBase = new OleDbCommand(" select * from iknow where Username = '"+user_NameTextBox.Text+"'");
cmdDataBase.Connection = conDataBase;
OleDbDataReader myReader;
conDataBase.Open();
myReader = cmdDataBase.ExecuteReader();
int count = 0;
while (myReader.Read())
{
count = count + 1;
}
if (count == 1)
{
MessageBox.Show("Login Successful");
}
else
{
MessageBox.Show("Invalid Username");
}
You have a couple issues, as Jon Skeet pointed out you've introduced a SQL injection vulnerability, aren't implementing the using syntax to dispose of resources correctly, and have a parameter but aren't actually implementing (this is hard to identify, without more code or what flagged this error).
var query = "SELECT TOP 1 [Id] FROM User WHERE Username = #Username";
using(var connection = new OleDbConnection(path))
using(var command = new OleDbCommand(query, connection))
{
connection.Open();
command.Parameters("Username", txtUsername.Text());
using(var reader = command.ExecuteReader())
while(reader.Read())
{
// Do something.
}
}
So the above code would address the following:
Injection point
Disposing resources
Correctly associating command to connection
No reason to * for everything, if you only want to see if it exists.
You should really only have a single username, so TOP 1 could refine.
You also could use ExecuteScalar instead of reader, that way you can simply validate the record was returned. This would alleviate the need to iterate through the returned record set. If you TOP 1 and ensure only one username exists, won't matter but it is an option.
As for your parameter, we would need more information. The debugger should tell you which line is throwing the exception. Those details could help resolve the issue.
When I run the following code:
query = "select count(*) from table where name = '?name'";
MySqlConnection connection =
new MySqlConnection(ConfigurationManager.ConnectionStrings["mydb"].ToString());
connection.Open();
MySqlCommand command = new MySqlCommand(query,connection);
command.Parameters.Add("?name", name);
Int32 number = command.ExecuteScalar();
number is always zero, even when cast to an int.
I have tried converting it to int64, no dice. I have tried command.Prepare(). I have tried using Convert.ToInt32() and every other variation. I have tried just about everything under the sun including quoting verbatim what this suggests and I get no dice. Trying to cast the object as an integer, as a long, as an int32, none of this seems to work. These results are always 0 or cause a MySQL error.
EDIT: Stack overflow will not format that code properly in code tags, i apologize
The reason for that is because the parameter is enclose with single quote thus making it a string. Remove it and it will work,
query = "select count(*) from table where name = #name";
MySqlConnection connection = new MySqlConnection(ConfigurationManager.ConnectionStrings["mydb"].ToString());
connection.Open();
MySqlCommand command = new MySqlCommand(query,connection);
command.Parameters.Add("#name", name);
for better code,
use using for proper object disposal
using try-catch block for proper handling of exceptions
code snippet,
query = "select count(*) from table where name = #name";
string connString =ConfigurationManager.ConnectionStrings["mydb"].ToString();
using(MySqlConnection connection = new MySqlConnection(connString))
{
using(MySqlCommand command = new MySqlCommand(query, connection))
{
command.Parameters.Add("#name", name);
try
{
connection.Open();
// other codes
}
catch(MySqlException ex)
{
// do somthing with the exception
// don't hide it
}
}
}
I need to retrieve a value from a field in database. I have the used following code. but the value checkOrderId (which I need) shows the SQL string instead of the value from database. I don't know why it is doing so. Could somebody help me please?
string connectionString = "Data Source = xxyyzz;Initial Catalog = xyz; Integrated Security = True";
SqlConnection connection = new SqlConnection(connectionString);
connection.Open();
string tableName = "[GIS].[SecondaryTraffic].[PotentialBackHauls]";
string checkOrderId = "Select TOP 1 OrderID From" + tableName + "ORDER BY InsertDate DESC";
SqlCommand cmd = new SqlCommand(checkOrderId, connection);
//cmd.ExecuteNonQuery();
OpenPop.Pop3.Pop3Client popConn = new OpenPop.Pop3.Pop3Client();
if (orderIdentity == checkOrderId)
{
popConn.DeleteMessage(messageNumber);
}
connection.Close();
I am new and dont have reputation to answer my question immediately. With everybody's help, i got this one solved...Great help, thanx everybody...following is my code.
string connectionString = "Data Source = EAEDEV;Initial Catalog = GIS; Integrated Security = True";
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
string tableName = "[GIS].[SecondaryTraffic].[PotentialBackHauls]";
string checkOrderId = "Select TOP 1 OrderID From " + tableName + " ORDER BY InsertDate DESC";
SqlCommand cmd = new SqlCommand(checkOrderId, connection);
string valueReturned = (string)cmd.ExecuteScalar();
OpenPop.Pop3.Pop3Client popConn = new OpenPop.Pop3.Pop3Client();
if (orderIdentity == valueReturned)
{
popConn.DeleteMessage(messageNumber);
}
connection.Close();
}
You need to execute the query and check the results, here you are just comparing a string with the query SQL.
Please see here
http://www.csharp-station.com/Tutorial/AdoDotNet/lesson03
for a tutorial.
Your expectation of the result being set into checkOrderId is incorrect. In this instance checkOrderId is just the query to execute and not the actual result.
You need to read the value back from executing the command:
using (var connection = new SqlConnection(connectionString))
using (var comm = new SqlCommand("Select TOP 1 OrderID From [GIS].[SecondaryTraffic].[PotentialBackHauls] ORDER BY InsertDate DESC", connection))
{
connection.Open();
object result = comm.ExecuteScalar(); // This is the key bit you were missing.
if (result != null)
{
// You can cast result to something useful
int orderId = (int)result;
}
} // Both comm and connection will have Dispose called on them here, no need to Close manually.
ExecuteScalar returns the value in the first cell (ie, column 1 row 1) as an object that you can cast to a better type (depending on what type it was in the result-set schema).
If you need to read multiple values, you need to look at ExecuteReader.
There are also other ways of doing this using output parameters, but that would pollute the point of the answer.
You can add space to your query
"Select TOP 1 OrderID From " + tableName + " ORDER BY InsertDate DESC";
Nota : I suggest you to use AddWithValue method with your parameter
string checkOrderId = "Select TOP 1 OrderID From #tableName ORDER BY InsertDate DESC";
SqlCommand cmd = new SqlCommand(checkOrderId, connection);
cmd.Parameters.AddWithValue("#tableName", tableName );
Link : http://msdn.microsoft.com/fr-fr/library/system.data.sqlclient.sqlparametercollection.addwithvalue.aspx
You don't actually run your command anywhere. Instead of the commented-out cmd.ExecuteNonQuery, you should look into the ExecuteScalar method, which allows you to read back a single result value from a query - which is what your query returns.
Add
int i = (Int32) cmd.ExecuteScalar();
right after
SqlCommand cmd = new SqlCommand(checkOrderId, connection);
then the variable i will contain the order id
No, this is not correct. You are comparing the variable orderId to your query string. I doubt that's what you want to do. I imagine you'd be better off calling cmd.ExecuteScalar() to retrieve the actual OrderID value. As noted by other answers, your query string is missing a space. But most importantly, it is bad practice to construct SQL queries in code. Although I can't see a security issue with this code, if you continue to use this method you will probably write code that is vulnerable to SQL injection. I recommend you learn to either use parameters or LINQ to build your queries.
Ok either I'm really tired or really thick at the moment, but I can't seem to find the answer for this
I'm using ASP.NET and I want to find the amount of rows in my table.
I know this is the SQL code: select count(*) from topics, but how the HECK do I get that to display as a number?
All I want to do is run that code and if it = 0 display one thing but if it's more than 0 display something else. Help please?
This is what I have so far
string selectTopics = "select count(*) from topics";
// Define the ADO.NET Objects
SqlConnection con = new SqlConnection(connectionString);
SqlCommand topiccmd = new SqlCommand(selectTopics, con);
if (topiccmd == 0)
{
noTopics.Visible = true;
topics.Visible = false;
}
but I know I'm missing something seriously wrong. I've been searching for ages but can't find anything.
PHP is so much easier. :)
Note that you must open the connection and execute the command before you can access the result of the SQL query. ExecuteScalar returns a single result value (different methods must be used if your query will return an multiple columns and / or multiple rows).
Notice the use of the using construct, which will safely close and dispose of the connection.
string selectTopics = "select count(*) from topics";
// Define the ADO.NET Objects
using (SqlConnection con = new SqlConnection(connectionString))
{
SqlCommand topiccmd = new SqlCommand(selectTopics, con);
con.Open();
int numrows = (int)topiccmd.ExecuteScalar();
if (numrows == 0)
{
noTopics.Visible = true;
topics.Visible = false;
}
}
ExecuteScalar is what you're looking for. (method of SqlCommand)
Btw, stick with C#, there's no way PHP is easier. It's just familiar.
You need to open the connection
This might work :
SqlConnection sqlConnection1 = new SqlConnection("Your Connection String");
SqlCommand cmd = new SqlCommand();
SqlDataReader reader;
cmd.CommandText = "select count(*) from topics";
cmd.CommandType = CommandType.Text;
cmd.Connection = sqlConnection;
sqlConnection1.Open();
reader = cmd.ExecuteReader();
// Data is accessible through the DataReader object here.
sqlConnection1.Close();
Similar Question: C# 'select count' sql command incorrectly returns zero rows from sql server
I need syntax help with the following code logic:
I have a code block that gets email address from the database. The email addresses need to be assigned to a string variable strEmailAddress with a comma seperation
My code is:
SqlConnection conn = new SqlConnection(strConn);
string sqlEmailAddress = "usp_Get_Email_Address";
SqlCommand cmdEmailAddr = new SqlCommand(sqlEmailAddress, conn);
cmdEmailAddr.CommandType = CommandType.StoredProcedure;
con.Open();
SqlDataReader sqlDREmailAddr = cmdEmailAddr.ExecuteReader();
How can I loop through the records and store the results in strEmailAddress seperated by comma?
while (sqlDREmailAddr.Read())
{
//...process each row here
}
I would also wrap the reader in a using statement to make sure it is closed properly:
using (SqlDataReader sqlDREmailAddr = cmdEmailAddr.ExecuteReader())
{
}
Depending on what the columns in your dataset is named, reading values from each record will look something like this (update: now with all addresses merged):
var emailAddress = new StringBuilder();
var emailAddressOrdinal = sqlDREmailAddr.GetOrdinal("EmailAddress");
while (sqlDREmailAddr.Read())
{
if (emailAddress.Length > 0)
emailAddress.Append(',');
emailAddress.Append(sqlDREmailAddr.GetString(emailAddressOrdinal));
}
Use the SqlDataReader.Read method:
while (sqlDREmailAddr.Read())
{
...
// Assumes only one column is returned with the email address
strEmailAddress = sqlDREmailAddr.GetString(0);
}
while (sqlDREmailAddr.Read())
{
// handle row here
}
This is what you're looking for....
using (SqlConnection conn = new SqlConnection(strConn)){
string sqlEmailAddress = "usp_Get_Email_Address";
using (SqlCommand cmdEmailAddr = new SqlCommand(sqlEmailAddress, conn)){
cmdEmailAddr.CommandType = CommandType.StoredProcedure;
conn.Open(); // Typo Glitch!
using (SqlDataReader sqlDREmailAddr = cmdEmailAddr.ExecuteReader()){
while(sqlDREmailAddr.Read()){
if (!sqlDREmailAddr.IsDBNull(sqlDREmailAddr.GetOrdinal("emailAddr"))){
// HANDLE THE DB NULL...
}else{
strEmailAddress = sqlDREmailAddr.GetSqlString(sqlDREmailAddr.GetOrdinal("emailAddr"));
// Do something with strEmailAddr...
}
}
}
}
}
Notice:
A typo glitch on the conn variable...
A check is made to ensure that the Database value returned is not NULL
A call is made to GetOrdinal to return the column based on emailAddr string value that corresponds to the column from the query for SQL Select...which is an int type) as the parameter for GetSqlString..
Edit: Thanks to John Saunders for pointing out a blooper!
Edit#2: Thanks to Peter Lillevold for pointing out a mis-spelling...
Hope this helps,
Best regards,
Tom.