As I am new to coding I have to get an id from user and compare it to a table from students that contains a foreign key of sectionid. I would really appreciate if you help me what to do next I have searched but I'm not understanding anything.
[HttpPost]
public ActionResult CheckSectionIDagainststudentID(string sectionID)
{
int x = Int32.Parse(sectionID);
ConnectionManager connManager = new ConnectionManager();
SqlConnection conn = connManager.GetConnection();
using (SqlCommand cmd = new SqlCommand())
{
cmd.CommandType = CommandType.Text;
cmd.CommandText = "Select * From Student Where sectionid = " + x;
cmd.Connection = conn;
conn.Open();
cmd.ExecuteNonQuery();
}
Although you MIGHT be close (not knowing all your tables), I would finish what you have using a SqlDataAdapter. That does a bunch of the work for you when loading into a table.
replace your "cmd.ExecuteNonQuery()" line with something like.
var sda - new SqlDataAdapter();
sda.Command = cmd;
var tbl = new DataTable();
sda.Fill( tbl );
This should pull down all records and put into a datatable object for you. Then you can go through each record and do whatever you need.
Also, fix your parameters. if expecting a number, do so. But from a web post, everything comes in as string and you need to parse as you have done. use int.TryParse() command (read up on that), to prevent crash if some bad text comes in unexpectedly.
Finally fix your query now and all future to prevent sql-injection. use place-holders and then your parameter, such as
cmd.CommandText = "Select * From Student Where sectionid = #parmSectionID";
cmd.Parameters.AddWithValue( "parmSectionID", x );
Dont add the "#" to the string representation in the parameters line.
Definitely read-up on more SQL commands throughout S/O and also SQL-Injection especially this early on in your development. Dont start with bad techniques that will bite you in the long run.
Related
I have a small table (tbl_user_favs) that is meant to store user favorites. Column 1 is the user ID, and then every column after that is a slot for a selected favorite PC to be stored, denoted Slot1, Slot2.
using (SqlConnection con = new SqlConnection(#"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\UserFavorites.mdf;Initial Catalog=tbl_user_favs;Integrated Security=True;Connect Timeout=30"))
{
string cmdString = ("SELECT * FROM tbl_user_favs WHERE UserID = '" + Globals.emailUID + "'");
SqlCommand cmd = new SqlCommand(cmdString, con);
cmd.Parameters.Add("#Slot1", SqlDbType.VarChar).Value = PCnum;
DataSet loginCredentials = new DataSet();
SqlDataAdapter dataAdapter;
con.Open();
//dataAdapter = new SqlDataAdapter(cmdString, con);
dataAdapter = new SqlDataAdapter(cmd);
dataAdapter.Fill(loginCredentials);
//cmd.ExecuteNonQuery();
con.Close();
}
Code executes, but it does not add the PCnum to the database next to the UserID. It should lok through the rows, find the UserID that matches the logged in user, Globals.emailUId, and add the PCnum to an open slot. Without worrying yet how to dynamically increment the Slots, why isn't this insert adding the PCnum to Slot 1? I've seen some tutorials use ExecuteNonQuery, and some use the dataAdapter, but both have the same result. I suspect there is something off with my SQL? Thank you
There are a couple things going on here.
First is that you are using "Parameters" incorrectly. It's supposed to add data to your query, not data to the database/row/column after a query has been made.
sql parameterized query in C# with string
Second, you are doing a select query, so you are only getting data from the db, not putting data into it.
To do what you want, you'd need to do this instead: (I don't have a good way to test this, so it may need tweaks, but it should be close.)
using (SqlConnection con = new SqlConnection(#"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\UserFavorites.mdf;Initial Catalog=tbl_user_favs;Integrated Security=True;Connect Timeout=30"))
{
string cmdString = ("UPDATE tbl_user_favs SET Slot1 = #Slot1 WHERE UserID = #EmailUID");
SqlCommand cmd = new SqlCommand(cmdString, con);
cmd.Parameters.AddWithValue("#Slot1", PCnum);
cmd.Parameters.AddWithValue("#EmailUID", Globals.emailUID);
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
You no longer need the DataSet or the SqlDataAdapter.
Since you seem to be confused on what parameterization is and why to use it, check out this question, too.
And here's just some more reading on the topic in general. I used these articles as resources for this answer:
https://visualstudiomagazine.com/articles/2017/07/01/parameterized-queries.aspx
https://www.c-sharpcorner.com/UploadFile/a20beb/why-should-always-use-the-parameterized-query-to-avoid-sql-i/
I am having an issue with the increment for the ID. The ID would increase by one every time I click insert, but the problem occurs when the ID 2, it would insert the values twice, if ID 3, it would insert the values three times, and so on.
There are couple of options that I have been trying. One is Max and the other one is finding the last inserted value and add one to the ID just.
I would appreciate if anyone can help me out with this. Thanks
public partial class LoginInfo : System.Web.UI.Page
{
static string myConnectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
private void GenerateID()
{
SqlConnection myConnection = new SqlConnection(myConnectionString);
string myQuery1 = "Select Count(S_ID) from Student_Name";
SqlCommand cmd = new SqlCommand(myQuery1, myConnection);
myConnection.Open();
int addOneS_ID_Table1 = Convert.ToInt32(cmd.ExecuteScalar());
myConnection.Close();
addOneS_ID_Table1++;
lblstdID.Text = addOneS_ID_Table1.ToString();
myConnection.Open();
cmd.CommandText = "Select Count(P_ID) from Student_Pass";
int addOneP_ID_Table2 = Convert.ToInt32(cmd.ExecuteScalar());
myConnection.Close();
addOneP_ID_Table2++;
lblstdPass.Text = addOneP_ID_Table2.ToString();
/*-----------------------------------------------------------------*/
//SqlConnection myConnection = new SqlConnection(myConnectionString);
//SqlCommand cmd = new SqlCommand("SELECT MAX(S_ID) as max_S_ID from Student_Name",myConnection);
//cmd.CommandType = CommandType.Text;
//myConnection.Open();
//lblstdID.Text = Convert.ToString(cmd.ExecuteScalar());
//cmd.CommandText = "SELECT MAX(P_ID) as max_P_ID FROM Student_Pass";
//lblstdPass.Text = Convert.ToString(cmd.ExecuteScalar());
//myConnection.Close();
}
protected void Page_Load(object sender, EventArgs e)
{
if(!IsPostBack)
{
GenerateID();
}
}
protected void btnInsert_Click(object sender, EventArgs e)
{
SqlConnection myConnection = new SqlConnection(myConnectionString);
string myQuery = "Insert into Student_Name(S_ID,STUDENT_NAME) VALUES" + "(#S_ID,#STUDENT_NAME)";
SqlCommand cmd = new SqlCommand(myQuery,myConnection);
cmd.Parameters.Add("#S_ID", SqlDbType.Int).Value = lblstdID.Text;
cmd.Parameters.Add("#STUDENT_NAME", SqlDbType.VarChar).Value = txtstdName.Text;
if(myConnection.State == ConnectionState.Closed)
{
myConnection.Open();
}
cmd.ExecuteNonQuery();
cmd.Parameters.Clear();
//Second Table
cmd.CommandText = "Insert into Student_Pass(P_ID,PASSWORD) VALUES" + "(#P_ID,#PASSWORD)";
cmd.CommandType = CommandType.Text;
cmd.Parameters.Add("#P_ID", SqlDbType.Int).Value = lblstdPass.Text;
cmd.Parameters.Add("#PASSWORD", SqlDbType.VarChar).Value = txtStdPass.Text;
cmd.ExecuteNonQuery();
cmd.Parameters.Clear();
myConnection.Close();
GenerateID();
lblResult.Text = "Successfully Saved";
GridView1.DataBind();
}
}
Problem is with your query since you are getting COUNT(S_ID) which is going to get you count of records doesn't necessarily will give exact ID number. You should rather try MAX(S_ID) or ORDER BY clause saying
Select MAX(S_ID) from Student_Name
(OR)
Select TOP 1 S_ID from Student_Name ORDER BY S_ID DESC;
But recommended, You should actually go with SQL Server ##IDENTITY or SCOPE_IDENTITY() to get the last inserted record ID (assuming that S_ID is an IDENTITY column)
It's highly recommended to not use max or top in order to determine the "next" identifier to use, simply because of the cost associated with it.
However, there are some other pitfalls to using max and top especially if there is a chance that nolock is used (which is a whole other conversation). I've seen a lot of web applications use max and has proven to be a performance killer.
Rahul is right, ##identity or scope_identity are good alternatives. However, I think this calls for using a native SQL Server sequence, which was introduced in SQL Server 2012. It was something that application developers have been waiting for and Microsoft finally delivered.
The issue with using ##identity or scope_identity is that you actually have to write rows to some table before you can even contemplate doing something.
This makes it a bit more costly and messier than what it may need to be. In the case of using a sequence, you can issue a new sequence number and then decide what to do and once you decide what to do you're still guaranteed that you're the only one with that sequence number.
You would create a sequence like this. You should check out the documentation as well.
create sequence dbo.StudentIdSeq
as int -- this can be any integer type
start with 1 -- you can start with any valid number in the int, even negative
increment by 1;
go
Then you issue new sequence numbers by doing this ...
select next value for StudentIdSeq;
It may still be good to create a stored procedure with an output parameter that you can call from C# (which is what I would do). In fact you may want to take it a step further, in the case that you have a bunch of sequences, and create a slick stored procedure that will get a new sequence based on the type that is being requested from the caller.
I have posted the code I have below
I am trying to get the data from an Access 2002-2003 database
If I take out everything after the WHERE clause and just use "SELECT * FROM [{0}] then it takes all the data from the table with no problems. I have double checked the field names, they are definitely correct. I have more than 1 table with the same field names, so I thought maybe I would need to include the table name before the field name, but with or without the table I still get the same exception. I have tried moving the position of the square brackets, again with no success...
Even if I include only one of the WHERE clauses, the code no longer works, and I can't for the life of me work out why.. I have spent hours looking at numerous posts here and on other sites related to this error, but none of the suggestions have helped me..
The Destination field is a 'memo' field in Access.
The Next Collection fields are date fields, GVars.currentDate is set earlier in the code to be today's date (with the time portion set to 00:00:00).
GVars.thisFY is also set programatically as a string prior to this.
Any tips would be appreciated.
string sql;
OleDbDataAdapter adapter;
sql = string.Format(
"SELECT * FROM [{0}] WHERE {0}.[Destination] = #Destination AND {0}.[Next Collection] BETWEEN #NextCollectionA AND #NextCollectionB"
, GVars.thisFY);
// Create the command object
OleDbCommand cmd = new OleDbCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = sql;
// Add values to the fields
cmd.Parameters.AddWithValue("#Destination", "Henwood");
cmd.Parameters.AddWithValue("#NextCollectionA", GVars.currentDate);
cmd.Parameters.AddWithValue("#NextCollectionB", GVars.currentDate.AddDays(1));
adapter = new OleDbDataAdapter(cmd.CommandText, conn);
System.Diagnostics.Debug.Print(cmd.CommandText);
try
{
adapter.Fill(ds);
GVars.bLblLastUpdate = DateTime.Now.ToString("HH:mm:ss");
}
catch (Exception ex)
{
}
EDIT:
Thanks Vladislav for the answer, corrected code posted below:
string sql;
OleDbDataAdapter adapter;
sql = string.Format(
"SELECT * FROM [{0}] WHERE [{0}].[Destination] = #Destination AND [{0}].[Next Collection] BETWEEN #NextCollectionA AND #NextCollectionB"
, GVars.thisFY);
// Create the command object
OleDbCommand cmd = new OleDbCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = sql;
cmd.Connection = conn;
// Add values to the fields
cmd.Parameters.Add("#Destination", OleDbType.Char).Value = "Henwood";
cmd.Parameters.Add("#NextCollectionA", OleDbType.DBDate).Value = GVars.currentDate;
cmd.Parameters.Add("#NextCollectionB", OleDbType.DBDate).Value = GVars.currentDate.AddDays(1);
adapter = new OleDbDataAdapter(cmd);
try
{
adapter.Fill(ds);
GVars.bLblLastUpdate = DateTime.Now.ToString("HH:mm:ss");
}
Try to specify types for the parameters you add.
Another thing I notice is that to your adapter you are passing only the CommandText.
You should pass the whole command object.
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();
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