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Do I have to Close() a SQLConnection before it gets disposed?
(8 answers)
Closed 9 years ago.
When using a using block for SQL connections in C#, does this also a close method? I'm asking as I need to explicitly use the con.Open() method. I found this example:
using (SqlConnection con = new SqlConnection(connectionString))
{
con.Open(); // open method
string queryString = "select * from db";
SqlCommand cmd = new SqlCommand(queryString, con);
SqlDataReader reader = cmd.ExecuteReader();
reader.Read();
??? // What about a close method?
}
Or does the using block close the connection itself?
using translates to:
SqlConnection con = new SqlConnection(connectionString)
try
{
con.Open(); <-- open method
string queryString = "select * from db";
SqlCommand cmd = new SqlCommand(queryString, con);
SqlDataReader reader = cmd.ExecuteReader();
reader.Read();
}
finally
{
if (con!= null)
((IDisposable)con).Dispose();
}
where ((IDisposable)con.Dispose(); closes what is to be closed.
You don't have to close it - using is enough. MSDN says:
To ensure that connections are always closed, open the connection inside of a using block, as shown in the following code fragment. Doing so ensures that the connection is automatically closed when the code exits the block.
No, you don't have to call the Close-Method of the SqlConnection.
When it gets disposed on the end of the using, it closes automatically.
(The Dispose-Method calls Close()) [1]
The other answers are correct, however, I want to be a bit more explicit.
The MSDN states the following:
Close and Dispose are functionally equivalent.
Because using using will call Dispose a separate call to Close is not needed.
when you use the 'using' keyword and create a connection in it .
the connection is open as far as there is the scope of the 'using' keyword when closing bracket is reached the connection is closed automatically as it was defined within a scope and the scope is not in exist
in other words treat it as the local variable which can be accessed within the scope only.
hope this will help.
Related
I have a stored procedure that I need to run in C# and set the result set returning from the SP in a HTML table. Please note that the SP is working well in SSMS and returning results.
The c# code I am using is (it is in an ASP 4.5 project):
SQLDatabase sqldb = new SQLDatabase();
using (SqlConnection sqlcn = new SqlConnection(sqldb.GetConnectionString().ToString()))
{
if (sqlcn.State == ConnectionState.Closed)
{
sqlcn.Open();
}
SqlCommand cmd = new SqlCommand("[MyStoredProcedure]", sqlcn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("#FromDate", Convert.ToDateTime(txtFrom.Value.ToString()));
cmd.Parameters.AddWithValue("#ToDate", Convert.ToDateTime(txtTo.Value.ToString()));
using (SqlDataAdapter a = new SqlDataAdapter(cmd))
{
DataSet ds = new DataSet();
a.Fill(ds);
dtExtra = ds.Tables[0];
}
}
This code above is returning 0 rows, even though the SP is working in SSMS. While debugging, the connectionstring and the parameters are coming all true, no issue. The connectionstring is:
<add name="DefaultDB" connectionString="Data Source=TestEnv;Initial Catalog=TestTable;Integrated Security=SSPI;" providerName="System.Data.SqlClient"/>
I don't understand what may cause this. I found the topic below, but I am using Integrated Security=SSPI in my connection string already, so it did not help me. Any advice would be appreciated.
ASP.NET stored proc call bringing back no rows, but does in Management Studio!
EDIT: SOLVED! Thanks #NineBerry. It turned into a between/and usage problem in SP. Changing txtTo.Value as: DateTime.Today.AddDays(1).ToString("yyyy-MM-dd"); in the code fixed the issue (It was DateTime.Today.ToString("yyyy-MM-dd") before, I should have included it in the code part, didn't think it is related to that, sorry). Better solution would be updating the SP using >= and <= instead of between/and keywords tho.
I would modify your code to simply be:
using(var dbConnection = new SqlConnection("..."))
using(var command = new SqlCommand(query, dbConnection))
{
dbConnection.Open();
...
}
Handling the connection pooling in the using block is always a good idea per Microsoft guideline:
To ensure that connections are always closed, open the connection
inside of a using block, as shown in the following code fragment.
Doing so ensures that the connection is automatically closed when the
code exits the block.
You are checking if the connection is closed, what if the connection is idle? By using the using syntax you implement dispose. So it will correctly close your connection, so you should not need to check if the connection is closed unless you are using a singleton for the connection.
After reading your question, you may have more than just the one issue I pointed out. I would recommend a service account with access the specific data you are seeking, that the application can access rather than integrated security.
In SSIS I have a connection defined with the following connection string:
Data Source=myserver;Initial Catalog=Spears;Provider=SQLNCLI11.1;Integrated Security=SSPI;Auto Translate=False;
i am attempting to use this connection from a script task:
ConnectionManager connectionManager = this.Dts.Connections["Spears"];
object acquireConnection = connectionManager.AcquireConnection(this.Dts.Transaction);
SqlConnection con = acquireConnection as SqlConnection;
con.Open();
On execution
connectionManager comes back as a fully populated ConnectionManager
object
acquireConnection is a System._ComObject
con is null
obviously opening con fails
Casting as OleDbConnection or OdbcConnection returns null as well.
What am I doing wrong ?
This problem occurs because you are using an OLEDB connection in the SSIS package instead of an ADO.NET one.
Once you change that, the code should work fine, even if Dts.Transaction is null.
There are a couple of issues. First, you have not instantiated new SqlConnection object as in SqlConnection con = new SqlConnection();
Second, unless the container is set to participate in a transaction, Dts.Transaction will be null and so the cast to a SqlConnection will be null. Transactions are supported by default, but unless a parent container starts it, there will be no shared transaction. This makes the examples from MS a little misleading.
I suggest going with the following. Supposing your connection manager is an OleDb connection, the add System.Data.Oledb to the usings:
OleDbConnection conn = new OleDbConnection(Dts.Connections[".\\sql2016.SSISAuditDB"].ConnectionString);
using (conn)
{
conn.Open();
OleDbCommand cmd = new OleDbCommand("SELECT 1", conn);
int val = (int)cmd.ExecuteScalar();
MessageBox.Show(val.ToString());
}
In the above code, we just grab the connection string from our connection manager and then create a new connection from it. Note that OleDbConnection implements IDisposable, so it can be wrapped in a using() block and it does not need to be explicitly closed. This is a good practice, because it means you will not need to have extra handling for closing the connection, for example if you added a catch block.
m
You're using SQLNCLI11.1 Provider with SqlConnection object. Change your DTS connection, use "ADO.NET Connection" and try it.
I have below code and I am getting exception:
There is already an open DataReader associated with this Connection which must be closed first.
I am using Visual Studio 2010/.Net 4.0 and MySQL for this project. Basically I am trying to run another SQL statement while using data reader to do my other task. I am getting exception at line cmdInserttblProductFrance.ExecuteNonQuery();
SQL = "Select * from tblProduct";
//Create Connection/Command/MySQLDataReader
MySqlConnection myConnection = new MySqlConnection(cf.GetConnectionString());
myConnection.Open();
MySqlCommand myCommand = new MySqlCommand(SQL, myConnection);
MySqlDataReader myReader = myCommand.ExecuteReader();
myCommand.Dispose();
if (myReader.HasRows)
{
int i = 0;
// Always call Read before accessing data.
while (myReader.Read())
{
if (myReader["frProductid"].ToString() == "") //there is no productid exist for this item
{
strInsertSQL = "Insert Into tblProduct_temp (Productid) Values('this istest') ";
MySqlCommand cmdInserttblProductFrance = new MySqlCommand(strInsertSQL, myConnection);
cmdInserttblProductFrance.ExecuteNonQuery(); //<=====THIS LINE THROWS "C# mySQL There is already an open DataReader associated with this Connection which must be closed first."
}
}
}
You are using the same connection for the DataReader and the ExecuteNonQuery. This is not supported, according to MSDN:
Note that while a DataReader is open, the Connection is in use
exclusively by that DataReader. You cannot execute any commands for
the Connection, including creating another DataReader, until the
original DataReader is closed.
Updated 2018: link to MSDN
Always, always, always put disposable objects inside of using statements. I can't see how you've instantiated your DataReader but you should do it like this:
using (Connection c = ...)
{
using (DataReader dr = ...)
{
//Work with dr in here.
}
}
//Now the connection and reader have been closed and disposed.
Now, to answer your question, the reader is using the same connection as the command you're trying to ExecuteNonQuery on. You need to use a separate connection since the DataReader keeps the connection open and reads data as you need it.
Just use MultipleActiveResultSets=True in your connection string.
Add MultipleActiveResultSets=true to the provider part of your connection string
example in the file appsettings.json
"ConnectionStrings": {
"EmployeeDBConnection": "server=(localdb)\\MSSQLLocalDB;database=YourDatabasename;Trusted_Connection=true;MultipleActiveResultSets=true"}
You are trying to to an Insert (with ExecuteNonQuery()) on a SQL connection that is used by this reader already:
while (myReader.Read())
Either read all the values in a list first, close the reader and then do the insert, or use a new SQL connection.
The issue you are running into is that you are starting up a second MySqlCommand while still reading back data with the DataReader. The MySQL connector only allows one concurrent query. You need to read the data into some structure, then close the reader, then process the data. Unfortunately you can't process the data as it is read if your processing involves further SQL queries.
This exception also happens if you don't use transaction properly. In my case, I put transaction.Commit() right after command.ExecuteReaderAsync(), did not wait with the transaction commiting until reader.ReadAsync() was called. The proper order:
Create transaction.
Create reader.
Read the data.
Commit the transaction.
You have to close the reader on top of your else condition.
In my case, I was awaiting an async call, but in the calling scope, I was not awaiting that method that I was making the call in. So, the calling scope was continuing on while my connection was still open.
called scope:
protected override async Task AfterProcessing()
{
var result = await Stats.WriteAsync();
Log.Information("Stopping");
}
calling scope:
public virtual async Task Run()
{
BeforeProcessing();
try
{
Process();
}
finally
{
AfterProcessing(); // this line was missing an "await"
}
}
There is another potential reason for this - missing await keyword.
I'm using SQLite3 database for a small level system. The problem is that when I try to rename the db file using IO file system, System.IO returns an exception that the file is being used by another process however I've already closed the connection using connection.Close() method. I searched on this topic but cold not find any thing useful for me. Someone please suggest me the right way to release an SQLite connection..
Thanks in Advance
One of the things I learned programming with SQLite is that closing the connection is simply not good enough. You need to wrap everything in a using block. Make sure your SQLiteConnection object is wrapped in a using block, your SQLiteCommand is wrapped in a using block and your SQLiteDataReader is wrapped in a using block. Your code should look similar to this:
using (var connection = new SQLiteConnection())
{
connection.ConnectionString = connectionString;
using (var command = new SQLiteCommand())
{
connection.Open();
command.CommandType = CommandType.Text;
command.CommandText = sql;
command.Connection = connection;
using (SQLiteDataReader reader = command.ExecuteReader())
{
if (reader.HasRows)
{
// Do something
}
}
}
}
ok now i am using the SQL database to get the values from different tables... so i make the connection and get the values like this:
DataTable dt = new DataTable();
SqlConnection connection = new SqlConnection();
connection.ConnectionString = ConfigurationManager.ConnectionStrings["XYZConnectionString"].ConnectionString;
connection.Open();
SqlCommand sqlCmd = new SqlCommand("SELECT * FROM Machines", connection);
SqlDataAdapter sqlDa = new SqlDataAdapter(sqlCmd);
sqlCmd.Parameters.AddWithValue("#node", node);
sqlDa.Fill(dt);
connection.Close();
so this is one query on the page and i am calling many other queries on the page.
So do i need to open and close the connection everytime...???
also if not this portion is common in all:
DataTable dt = new DataTable();
SqlConnection connection = new SqlConnection();
connection.ConnectionString = ConfigurationManager.ConnectionStrings["XYZConnectionString"].ConnectionString;
connection.Open();
can i like put it in one function and call it instead.. the code would look cleaner...
i tried doing that but i get errors like:
Connection does not exist in the current context.
any suggestions???
thanks
You can definitely share the "open connection" code, no reason to duplicate it.
With the SQL Server provider for ASP.NET, there is very little overhead with "closing" the connection every time. It just returns the connection to your process' connection pool (see here), so opening the next connection will use very little overhead. I think it is good practice to close the connection after each operation
I use "using". You can include as many queries as you like inside. When complete it will clean up for you.
using (SqlConnection cn = new SqlConnection(connectionString))
{
using (SqlCommand cm = new SqlCommand(commandString, cn))
{
cn.Open();
cm.ExecuteNonQuery();
}
}
Typically yes, you make individual connections for multiple rowsets.
If you can use joins to produce a single meaningful rowset, that's typically a good thing to do on the server side instead of the client side.
You may also want to look at making multiple connections and using the async features in order to queue all your requests simultaneously instead of sequentially - have a look at this article.
No you do not have to open and close the connection every time as long as you are using the same database. What you need to change is the
sqlCommand's queryString every time.
Like what #durilai said, [using] is useful. Using actually has more functions than this, but essentially it puts a try/catch block around your code and calls dispose to close the connection in this case.
Anything that needs open/close can be used with using, so things such as text writers, or other objects.