I am having a problem with LAST_INSERT_ID().
Every time I use it I need to open and close a new connection.
This slows down my application a great deal.
i need to do many insert statements end get for each one his inserted id
all on the same connection!
How can I get the last inserted ID on the same connection
for with MySQl, ODBC and C# from a specific table with no concurrency problems?
here is my code:
#region Private Variables
private static DataAccess _DataAccess = null;
private static object _SyncLock = new object();
private OdbcConnection myConnection = null;
#endregion
#region Instance Method
public static DataAccess Instance
{
get
{
lock (_SyncLock)
{
if (_DataAccess == null)
_DataAccess = new DataAccess();
return _DataAccess;
}
}
}
#endregion
#region Constractors
public DataAccess()
{
myConnection = new OdbcConnection(stringConnDB);
myConnection.Open();
}
#endregion
Every time I use it i need to open and close a new connection
No, you don't need a new connection. You are supposed to use it on the same connection just after an insert statement.
From the manual:
The ID that was generated is maintained in the server on a per-connection basis. This means that the value returned by [LAST_INSERT_ID] to a given client is the first AUTO_INCREMENT value generated for most recent statement affecting an AUTO_INCREMENT column by that client. This value cannot be affected by other clients, even if they generate AUTO_INCREMENT values of their own. This behavior ensures that each client can retrieve its own ID without concern for the activity of other clients, and without the need for locks or transactions.
Why do you think that you need to open a new connection? Actually you should not open a new connection, you should use last_insert_id() on the same connection to be sure to get the correct result.
If you have tried it with a new connection and it seems to work, then it's only because the connections are pooled, and you happen to get the same connection the second time. When you start to use this with more than one single user, it will fail.
Related
A program written in C# Oracle client that proved to have "Connection leak" which it is not closing all database connections and so after some time it can no longer connect to the database as there are too many open connections.
I wrote the following helper function (quite expansive):
private static int tryFindConnCount(){
var connstk = new Stack<Oracle.ManagedDataAccess.Client.OracleConnection>();
try
{
for (var i = 0; i < 10000; ++i)
{
var conn = new Oracle.ManagedDataAccess.Client.OracleConnection(
myDatabaseConnection);
conn.Open();
connstk.Push(conn);
}
}
catch(Exception e)
{
foreach (var conn in connstk)
{
conn.Close();
}
}
return connstk.Count;
}
Here is the code in a test case that uses the above:
var co = tryFindConnCount();
CodeThatMayLeakConnection();
var cn = tryFindConnCount();
Assert.That(cn, Is.EqaulTo(co));
It helped me identify at least one case that have connection leak.
The problem of tryFindConnCount is that it should never be used in production. And I think there should be some way to obtain the same value much cheaper.
How can I do this in the code so I can monitor this value in production?
Trying to find places where connections where not closed is a difficult task.
If you leave the program and forget to close the connection the last sql which was executed is stored in column SQL_ID in v$session (gv$session for RAC). You can search v$session for idle/dead sessions. You can then use v$sql to find the SQL text which may tell you more about what was done last. By this you may get a hint where to search in your code.
select a.sid, a.username, a.program, a.machine, a.sql_id, b.sql_fulltext
from v$session a, v$sql b
where b.sql_id(+) = a.sql_id
and a.username is not null -- filter system processes, maybe filter more stuff
;
You can query Oracle DB on "gv$session" view to get the info that you need. With a query on this view you can cyclically monitor the DB every 10-15 minutes for a count of connections from this program.
Example query below :
select count(*)
from gv$session
where machine = 'XXXXX'
and username = 'YYYYY'
and program = 'ZZZZZ';
You only need values that uniquely identify those connections like for example machine from which the connections originate.
Also the query is very light and doesn't add performance overhead.
I'm a beginner.
I already found a way to connect to SQL SERVER using the codes below:
private void getListBtn_Click(object sender, RoutedEventArgs e)
{
SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=myDB;Integrated Security=true;");
SqlDataAdapter sda = new SqlDataAdapter("SELECT ID,Date,Name,City FROM Info;", con);
DataTable dt = new DataTable();
sda.Fill(dt);
dataGridForm.ItemsSource = dt.DefaultView;
I also wanted to get number of rows from a TABLE and set it to a label, But it's not a good idea to copy and paste this code again, I want to have a method for sqlconnection so i won't rewrite this code again and again for every single query.
Sorry i'm an absolute beginner, 3 days since i started learning C# WPF.
Yes some frameworks and/or ADO's solutions are good and maybe the best "professionnal" approch, you say you're a beginner and I was it not so far ;-).
So the simpliest way is to add a new class for the sql connection. In example add a Sqlconnect.cs class.
using System.Data.SqlClient;
public class Sqlconnect
{
public SqlConnection Con { get; set; }//the object
private string conString { get; set; }//the string to store your connection parameters
}
This class will have a method to open the connection and one to close it.
public void conOpen()
{
conString = "Data Source=..."; //the same as you post in your post
Con = new SqlConnection(conString);//
try
{
Con.Open();//try to open the connection
}
catch (Exception ex)
{
//you do stuff if the connection can't open, returning a massagebox with the error, write the error in a log.txt file...
}
}
public void conClose()
{
Con.Close();//close the connection
}
In your other(s) classe(s) where you need a sql query you first instantiate an new object.
private void getListBtn_Click(object sender, RoutedEventArg e)
{
Sqlconnect con = new Sqlconnect();//instantiate a new object 'Con' from the class Sqlconnect.cs
con.conOpen();//method to open the connection.
//you should test if the connection is open or not
if(con!= null && con.State == ConnectionState.Open)//youtest if the object exist and if his state is open
{
//make your query
SqlDataAdapter sda = new SqlDataAdapter("your query", con);
//etc
con.conClose();//close your connection
}
else
{
//the connection failed so do some stuff, messagebox...as you want
return;//close the event
}
}
this example need some ameliorations, it's evident but I wrote it like this to be clearest.
First thing this is not related to WPF, this is general coding even I would not consider this to be related to .net.
For your current problem to show the count, you dont have to make a call again. You can get the count from the datatable row count. But, I would suggest few things:
You should have one or different separate layers like business, data access etc. as per your needs.
You should not give the connection as the way you have provided here.
You can choose to use any ORMs like entity framework, NHibernate etc based on your needs. This just a direction, you can choose to stick with ADO.Net as you have it your choice. But I would definitely suggest to throw in more layers to avoid duplicate codes and more structured approach.
Best choice if you don't need so much performance is ORM like Entity Framework.
Here is something of basics.
Just use it like in MVC app.
If we copy paste your code, then the error is appearing. I have corrected it and maybe others don't need to struggle like me to find this. :)
// Object exists and State is open
if (Conex != null && Conex.Con.State ==
System.Data.ConnectionState.Open)
{
// Create a String to hold the query
string query = "insert into Xray_Table values
(25,'zzz','hij',3,'uuu',6,'2012-06-18
10:34:09.000')";
// Create a SqlCommand object and pass the constructor the connection string and the query string
SqlCommand queryCommand = new SqlCommand(query, Conex.Con);
// Execute the query to update to the database
queryCommand.ExecuteNonQuery();
// method to close the connection.
Conex.conClose();
}
I'm setting up a connection factory for a .NET project, and I'd like to ask what is the best way for it.
I have an issue with the previous Log class not being able to write the logs properly because of table LOCKS (or so they say), so I'm tasked with setting up a new data layer that (hopefully) solves this along some other minor issues.
For now, the code:
public sealed class ConnectionFactory
{
//Will be SQL only
private static SqlConnection sqlConnection = null;
private static string connectionString = ConfigurationManager.ConnectionStrings["Development"].ConnectionString;
public static SqlConnection GetConnection()
{
if(sqlConnection == null)
{
sqlConnection = new SqlConnection();
sqlConnection.Open();
}
return sqlConnection;
}
}
I'll be using mostly procedures, but may have one or another weird request and we'll type a query if needed, so I'm think I have to add a SqlCommand somehow:
private static SqlCommand sqlCommand = null;
public static SqlCommand GetCommand()
{
//Check if sqlConnection is not null (omitted)
if(sqlCommand == null)
{
sqlCommand = sqlConnection.CreateCommand();
}
return sqlCommand;
}
However, should this command be static? Or should I create a new one each time a new query is going to be executed?
Thinking in avoiding locks mostly, can it be caused by having multiple commands or only multiple connections? How do I avoid and deal with this properly?
I believe a "nolock" would work in this case...
FROM [table] with (nolock)
whenever you do a direct query.
I am having some issues with a class that I have created to perform different database commands.
1st) The program is local ran, and will only run locally. It will only ever connect to the database on the localhost.
Therefore I have a simple class setup, called databaseConnector that allows me to pass a string to it with the required Mysql query to perform the different functions.
For instance.
I use:
var db = new databaseConnector();
db.Update("UPDATE * WHERE.....");
However, it seems if I ever want to use a different query, or another query, it's not working and throwing errors.
For instance.
var db = new databaseConnector();
db.Update("UPDATE * WHERE...");
db.INSERT("INSERT INTO * WHERE.....");
Will give me an error on the insert execution. Any ideas why? I have resorted to creating it again. So I have to redo:
db = new databaseConnector();
to then use the Insert command.
Here is an example of my insert function.
public void Insert(string query)
{
//open connection
if (this.OpenConnection() == true)
{
//create command and assign the query and connection from the constructor
MySqlCommand cmd = new MySqlCommand(query, connection);
//Execute command
cmd.ExecuteNonQuery();
//close connection
this.CloseConnection();
}
}
Now that I think about it. Should I call my db.openConnection() before doing it. Since when I initialize it in the first var db = new databaseConnection(), it's opening? And then in each function it's closing it, but only checking if it's open, instead of attempting to open, doing query, then closing.
I got some data inputed by the user that should be added to a Database File (.sdf). I've choose Sql Server CE because this application is quite small, and i didn't saw need to work with a service based database.
Well any way.
Here goes the code:
public class SqlActions
{
string conStr = String.Format("Data Source = " + new System.IO.FileInfo(System.Reflection.Assembly.GetExecutingAssembly().Location).DirectoryName + "\\basedados.sdf");
public SqlCeConnection SQLCEConnect()
{
SqlCeConnection Connection = new SqlCeConnection(conStr);
Connection.Open();
return Connection;
}
public Boolean AdicionarAuditorio(string Nome, int Capacidade)
{
string Query = "INSERT INTO auditorios (nome, capacidade) VALUES (#Nome, #Capacidade)";
using (var SQLCmd = new SqlCeCommand(Query, SQLCEConnect()))
{
SQLCmd.Parameters.AddWithValue("#Nome", Nome);
SQLCmd.Parameters.AddWithValue("#Capacidade", Capacidade);
if (SQLCmd.ExecuteNonQuery() == 1)
{
return true;
} else {
return false;
}
}
}
}
I use the AdicionarAuditorio(string Nome, int Capacidade) function to Insert the data. running ExecuteNonQuery() which is supposed to return the number of affected rows after he as run the query.
So it should return 1 if the query as successful, right?
In the end he returns 1, but if I browser the table data, the data that the query should add isn't there.
So whats wrong here?
NOTE. If your thinking that the
problem is the connection: I can't see
why is the problem once i got some
Select statements that use that
connection function SQLCEConnect()
and they all work pretty well.
Thanks in advance.
Are you sure you are looking at the right file? When you build your app in VS, it copies the SDF file as content to the target folder, so the database in your project will not reflect any updates. Your code is picking up the the file location there.
This is btw not a good practice, because once deployed, the program folders are not writable to your app (could this be the problem - did you already deploy?). Instead, the database file should reside in your appdata folder.
Is it possible that you make the call to AdicionarAuditorio in a TransactionScope without calling transactionScope.Complete()?