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First, thank you for suggestions. So: Conexiune is a class. getConnection() is a function that makes the connection and return true if connection is opened. So I can't use that var connection . I used this code in other forms and it worked..I want to update indexrow column with the value of int variable idintrebare ..So I rewrite your code like this:
string update = "UPDATE questions SET indexrow=@idintrebare WHERE id=@idintrebare;";
using (var connection = Conexiune.getConnection())
using (SQLiteCommand cmd = new SQLiteCommand(update, connection))
{
connection.Open();
cmd.Parameters.AddWithValue("@idintrebare", idintrebare);
cmd.ExecuteNonQuery();
}
,but I receive Operation is not valid due to the current state of the object .
Conexiune class looks like this: (This is good)
private static string conn = @"Data Source=database.db;Pooling=true;FailIfMissing=false;Version=3;";
public static SQLiteConnection connect = null;
private Conexiune() { }
public static SQLiteConnection getConnection()
{
SQLiteConnection connect = null;
try
{
connect = new SQLiteConnection(conn);
connect.Open();
return connect;
}
catch (SQLiteException e)
{
throw new Exception("Cannot connect", e);
}
}
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getConnection() returns an SQLiteConnection (not true/false).
So you can use that using (var connection = Conexiune.getConnection()) -line.
But as I see in that Conexiune-class, it already opens the connection for you. So the (new) error you're getting probably happens on my connection.Open() -line. Please remove that line and see what happens.
As I've seen from your reply to Richard Deeming, who suggested almost the same new code as me, you still get the old error there. This makes me believe the cause is one of those listed on the page that Simon_Whale linked for you. Do you maybe have an open Select-query while you click on the button that calls updateIndex() ?
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
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I removed that line and now database is still locked. Well, I have another function which selects data from table and is called by pressing on another button, but even if I don't press that button and try to call updateIndex() just after form loads, I still got the error..
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Do you possibly have some Select-query that is executed in your program's startup-code (so it get's executed no matter what) ? If yes, you might comment that out for testing. Maybe you don't close the reader of that query properly so that it's still open when trying to execute updateIndex().
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
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I am sure..Where I have used DataReader, I used CommnadBehavior.CloseConnection and after that I closed the reader. For example:
string selectareLicenta = "SELECT licenta FROM licente WHERE licenta = '" + maskedTextBox1.Text + "'";
using (SQLiteCommand cmd = new SQLiteCommand(selectareLicenta, Conexiune.getConnection()))
{
using (SQLiteDataReader read = cmd.ExecuteReader(CommandBehavior.CloseConnection))
{
if (read.Read())
{
SimulatorManager.Licenta = read["licenta"].ToString();
}
read.Close();
}
}
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I don't think this is the issue but for good practice you should change this like so:
string selectareLicenta = "SELECT licenta FROM licente WHERE licenta = '" + maskedTextBox1.Text + "'";
using (SQLiteConnection conn = Conexiune.getConnection())
using (SQLiteCommand cmd = new SQLiteCommand(selectareLicenta, conn))
using (SQLiteDataReader read = cmd.ExecuteReader(CommandBehavior.CloseConnection))
{
if (read.Read())
{
SimulatorManager.Licenta = read["licenta"].ToString();
}
}
..and you also should use an Sql-Parameter here.
Regarding the actual problem: I would suggest you double-check that all parts of your code where you run a select-query look like the above to ensure that the reader and connection get properly closed.
For the purpose of testing you could execute an update-statement as the very first action in your program and see if that works.
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
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Very good idea, I will try it right now!
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I tried to run the update on form loading and I get the error. It means that the error can be from the form that opens this form? Because I checked there and I have used using for everything and is ok..
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Hmm. And there's nothing database-related happening before that in your code?
Could probably another program be running and accessing the same database? Maybe there's some "zombie"-process of your program still running and keeping a connection to the database alive. See if rebooting Windows solves the issue.
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
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It's ok, I have found the error! In class cs where I have static void Main() , this is the main class of the project, I have this code:
string selectutilizator = "SELECT * FROM accounts";
using (SQLiteCommand selcom = new SQLiteCommand(selectutilizator, Conexiune.getConnection()))
{
using (SQLiteDataReader read = selcom.ExecuteReader())
{
if (read.HasRows)
{
Application.Run(new Elev());
}
else Application.Run(new Intro());
}
}
But I need this for the program..what is wrong there?
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Yep, that's the problem, most certainly. Application.Run(..) is a blocking call, so the DataReader is alive all the time. Just declare a boolean variable hasRows at the top of this code, assign read.HasRows to it after ExecuteReader(), move the if-else out of the using-blocks and use the boolean variable there instead of the reader.
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
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Yes, you right. Thank you very much! This is the solution:
string selectutilizator = "SELECT * FROM accounts";
bool hasrows=false;
using (SQLiteCommand selcom = new SQLiteCommand(selectutilizator, Conexiune.getConnection()))
{
using (SQLiteDataReader read = selcom.ExecuteReader())
{
if (read.HasRows)
{
hasrows=true;
}
}
}
if (hasrows) Application.Run(new Elev());
else Application.Run(new Intro());
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DPaul1994 wrote: Yes, you right. Thank you very much! You're welcome!
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
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Your code is vulnerable to SQL Injection[^].
NEVER use string concatenation to build a SQL query. ALWAYS use a parameterized query.
private void updateIndex()
{
const string update = "UPDATE questions SET indexrow = @idintrebare WHERE id = @idintrebare";
using (SQLiteCommand comp = new SQLiteCommand(update, Conexiune.getConnection()))
{
comp.CommandType = CommandType.Text;
comp.Parameters.AddWithValue("@idintrebare", idintrebare);
comp.ExecuteNonQuery();
}
}
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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I want to run flash file formats: *.swf in winform (VS2005), the toolbox click on All windows forms and select Choose Items ..., select tab: COM Components, browse and select the area marked "Shockwave Flash Control" , then click Macromedia Flash Object Factory and it was dragging on winform error "Failed to import the ActiveX control. Please ensure it is properly registered" winxpsp3 machine I use, how to register to use the flash file above I do ?
http://imagizer.imageshack.com/img661/3521/XzARIi.jpg
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I miss the logic of the official story that a base constructor is not inherited. If a class is able to call its base constructor (accessible) then why it is said the constructor is not inherited. The logic seems to be based on the fact that a base constructor has to be called explicitly, meaning the compiler will not call it automatically (ignore special cases). But the definition of inheritance is not based on the automatic calling.
modified 22-Apr-15 9:49am.
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The question assumes an instance constructor. A static constructor is not meant to be called by any outside code or any other class (derived or not derived), it is called only once by the loader, so the issue of derivation is totally moot for static constructor.
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And my answer applies to instance constructors -- in C#.
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That just sounds wrong.
From the C# 5 lang spec: section 1.6.6.3
The ... constructor (which is like an instance method) ...
Because the constructor is an instance member, it is permitted to access both the ... instance field and the ... static field.
The constructor has access to all of the instance's fields and properties and even instance methods.
Section 1.6.7.1
Unlike other members, instance constructors are not inherited, and a class has no instance constructors other than those actually declared in the class. If no instance constructor is supplied for a class, then an empty one with no parameters is automatically provided.
Section 10.11.1:
If an instance constructor has no constructor initializer, a constructor initializer of the form base() is implicitly provided. Thus, an instance constructor declaration of the form
C(...) {...}
is exactly equivalent to
C(...): base() {...}
A positive attitude may not solve every problem, but it will annoy enough people to be worth the effort.
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As I recall, the default base ctor is always called first, at least it is if the base class contains instance properties that need initialization.
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CRobert456 wrote: The logic is based on the fact the a base constructor has to be called explicitly, meaning the compiler will not call it automatically That would mean that all objects (!) would inherit the default constructor. That'd be a bit impractical.
You can add code to call an inherited constructor in your class, even if there's a different signature.
Bastard Programmer from Hell
If you can't read my code, try converting it here[^]
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First, I have a button that calls 2 functions. First function (calculateMedieSim()) makes an operation with two number and the second one (selectData()) selects data from tabel. totalsim = 15 and totalsimyes = 8. The result should be 53,3 but it shows 0 Why?
private void button1_Click(object sender, EventArgs e)
{
selectData();
calculateMedieSim();
}
private void selectData()
{
string select = "SELECT * FROM accounts WHERE id=1";
using (SQLiteCommand cmd = new SQLiteCommand(select, Conexiune.getConnection()))
{
using (SQLiteDataReader read = cmd.ExecuteReader())
{
if (read.Read())
{
totalsim = (int)read["totalsim"];
totalsimyes = (int)read["totalsimyes"];
}
}
}
}
private void calculateMedieSim()
{
medie_sim = (totalsimyes / totalsim) * 100;
sansa_examen = Math.Round(medie_sim, 2);
Console.WriteLine(sansa_examen);
}
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