I have the code below to query records from a stored procedure but am concerned I may not be disposing what I need to or am disposing when the object would be cleared by the Garbage Collector shortly afterward anyway.
Do I need to dispose the SqlDataReader since it is within the try catch block?
Do I need to run both cmd.Dispose and cmd.Connection.Close or does one infer the other?
Would the garbage collector eventually dispose of all these objects anyway (maybe not timely enough) or do these objects implictly require dispose possibly because of using unmanaged code?
public void GetData(string studentID)
{
SqlCommand cmd = new SqlCommand("sp_stored_proc",
new SqlConnection(Settings.Default.connectionString))
{ CommandType = CommandType.StoredProcedure };
try
{
cmd.Connection.Open();
cmd.Parameters.AddWithValue("#student_id", studentID);
SqlDataReader dr = cmd.ExecuteReader();
//do something with the data
if (dr != null)
dr.Dispose();
}
catch
{
//error handling
}
finally
{
if (cmd != null)
{
cmd.Dispose();
cmd.Connection.Close();
}
}
}
You should dispose the data reader, and the command. No need to separately close the connection if you dispose the command. You should ideally do both using a using block:
using (SqlCommand cmd = new...)
{
// do stuff
using (SqlDataReader dr = cmd.ExecuteReader())
{
// do stuff
}
}
If you need exception handling do that separately either inside or around the using blocks - no need for the finally for the Dispose calls though with using.
If you use something like this:
public void GetData(string studentID)
{
using (SqlConnection connection = new SqlConnection(Settings.Default.connectionString))
{
connection.Open();
using (SqlCommand command = connection.CreateCommand())
{
command.CommandType = CommandType.StoredProcedure;
command.CommandText = "sp_stored_proc";
command.Parameters.AddWithValue("#student_id", studentID);
using (SqlDataReader dataReader = command.ExecuteReader())
{
// do something with the data
}
}
}
}
then all of your Disposable objects will get disposed of correctly. Calling Dispose() on the SqlConnection, SqlCommand and SqlDataReader objects (which is what the using block does when it exits) closes them correctly.
Additionally, this approach keeps all of your variables scoped to where they are used.
The downside to this approach is that if you need error handling using a try/catch, you have to either wrap it around the whole method body, or use several of them to handle connection errors differently from reading errors, etc...
Do I need to dispose the SqlDataReader
since it is within the try catch
block?
-- Yes, as being inside of the try catch will not call the dispose method.
Do I need to run both cmd.Dispose and cmd.Connection.Close or does one infer the other?
-- Yes, you need to run both. Calling Cmd.dispose does not close the connection.
The dispose method is meant to be used by the programmer to clean up resources which either aren't directly managed by the garbage collector, or the need to be cleared out after the program is done using them to free up space. Technically, one could set up the program so the GC would handle it's disposal, but that's an assumption I wouldn't make, especially since the programmer writing the class exposed the dispose method for you. Putting the Command in a using statement is probably the easiest route, because you know it will get disposed when the code leaves the declaration space.
using (var connection = new Connection ())
{
using (var cmd = new Command())
{
}
}
Personally if something has a dispose method then it is worth using it anyway as they will prevent protential memory leaks.
To make a long story short; if it implements IDisposable, you should call Dispose.
Even if you use Reflector to figure out that Dispose in one object invokes Dispose on another object, I would still recommend to call Dispose on both, since this is internal implementation details that may change in some future release, so you should not rely on that always being true.
So, Dispose anything that is IDisposable.
you should open Connection firstly by Connection.Open();
then use the methods such as SqlDataReader to read
after all,close SqlDataReader firstly and then close connection
you can use keyword "using" to dispose it, but it is not a good idea
in fact the keyword "using" is to dispose the object automatically.
in other word,the object should achieve dispose method
Related
I was using this code:
public class SQLConnection : IConnection
{
private SqlConnection _sqlConnection = null;
//bunch of interface implementations for my project
//the destructor
~SQLConnection()
{
if(_sqlConnection != null)
{
if(_sqlConnection.State == ConnectionState.Open)
{
_sqlConnection.Close();
}
_sqlConnection.Dispose();
}
}
}
This was working well until some time ago, when I started receiving this error: Internal .Net Framework Data Provider error 1
After googling a bit, I found this link (the Caution part) and I think that's what's happening to me.
My class was managing the connection state opening and closing each time, but now that it seems I can't manage it this way, is there any other way that I can do this without having to go to every function that I use the connection and call connection.Close() explicitly?
Always use 'using' for safely disposing the connections.
using(var _sqlConnection = new SqlConnection())
{
//code here
_sqlConnection.Open();
}
//Safely disposed.
Also, it is never a good idea to use destructor explicitly in C# code unless you have unmanaged code.
You're probably receiving this error when one code is trying to access SQLConnection that has been already garbage collected. This usually will happen in cases like this one
SqlConnection sqlConn;
using (var sqlConnection = new SqlConnection())
{
sqlConn = sqlConnection;
sqlConnection.Open();
}
sqlConn.Close();
I know this example looks silly as it's overly simplified, but it happens often when programmers tend to share a connection object between Managing Classes. Look for any recent changes in your code. Maybe you're passing an instance of a connection between multiple objects. One of those objects gets Garbage Collected and in turn the connection gets disposed too.
I'm having some trouble. I have a SqlCommand in a using block. Usually this works fine. This time however, the code exits the using block but the command does not get disposed. It has me stumped.
using (SqlCommand transferCommand = new SqlCommand(strHeaderStoredProcedure, connection))
{
transferCommand.CommandType = System.Data.CommandType.StoredProcedure;
transferCommand.Parameters.Add("#InvtTransferID", SqlDbType.UniqueIdentifier).Value = InvtTransferID;
SqlDataReader transferReader = transferCommand.ExecuteReader();
while (transferReader.Read())
{
//do my stuff, this all works fine
}
}
using (SqlCommand transferCommand = new SqlCommand(strDetailsStoredProcedure, connection))
{
transferCommand.CommandType = System.Data.CommandType.StoredProcedure;
transferCommand.Parameters.Add("#InvtTransferID", SqlDbType.UniqueIdentifier).Value = InvtTransferID;
SqlDataReader transferReader = transferCommand.ExecuteReader(); <-- Error happens here.
}
I'm trying to reuse my connection to run a bunch of stored procedures. It is the strangest thing. I have some code on another form that is virtually identical and it runs fine, disposing the command and allowing me to make another. Any ideas what I'm doing wrong? (I'm trying to make this code look nice in the post but it seems to be beyond my meager power...so sorry for the messy code.)
Error is: There is already an open DataReader associated with this Command which must be closed first.
What you have is an open SqlDataReader (transferReader), Close and Dispose the datareader or use a using() for it.
I assume the command is not being released because the reader is still open.
As a bit of extra info, here is what the compiler does behind the scenes when you write an using statement.
using(IDisposable x)
{
//some work here
}
Turns into
IDisposable x = //some IDisposable
try
{
//do work here
}
finally
{
x.Dispose()
}
As Gusman mentioned , using cannot guarantee the object destruction, it just calls the object's dispose method. It's the IDisposable's reponsability to clean up any used resources
I hope this helps
I'm refactoring some old code as we're periodically having connection pool issues on a clients site.
While some code has wrapped DB connections in try/catch blocks I'll be using the using(){} thing (is there a proper term for this?)
So I'd like some clarification on how to use it in our situation to make as few changes as possible.
What we currently have is (mostly) something like this:
SqlConnection sqlConn = new SqlConnection();
SqlCommand sqlCmd = new SqlCommand();
try
{
// DB stuff here
}
finally
{
sqlCmd.Dispose();
sqlConn.Dispose();
}
Some connections aren't wrapped up at all.
So, I'm thinking of changing it to this:
using (SqlConnection ThisConnection = new SqlConnection(ConnectionString))
{
using (SqlCommand sqlCmd = new SqlCommand())
{
sqlCmd.Connection = ThisConnection;
// DB stuff here
}
}
I've tried this and it works. But I know there's a difference between something working and something working well :)
So, a few questions:
If the SqlConnection is assigned to SqlCommand.Connection and I only wrap up the SqlCommand in a using, will the connection be closed and disposed then the SqlCommand is?
If not, is the above code ok? Or should the SqlCommand using be before the SqlConnection or does it not matter?
When the object is disposed at the end of the using is this absolutely guaranteed to close the DB connection?
All feedback greatly appreciated, cheers.
The using approach is preferable; much harder to get it wrong and leave scenarios where objects can escape without being disposed. Unless you have a very specific reason, it should be your default. You can reduce the nesting, though:
using (SqlConnection ThisConnection = new SqlConnection(ConnectionString))
using (SqlCommand sqlCmd = new SqlCommand())
{
sqlCmd.Connection = ThisConnection;
// DB stuff here
}
When the object is disposed at the end of the using is this absolutely guaranteed to close the DB connection?
It will dispose it; the underlying connection (via any of these approaches) will usually still be pooled, though.
Of course, I also submit that the easiest way to do this is to use less code - less to get wrong. For example, I'd be very tempted to use "dapper", which avoids the need to mess with the commands, readers, parameter collections, etc:
int id = 123;
string name = "abc";
using (var conn = new SqlConnection(ConnectionString))
{
conn.Execute("Some TSQL", new { id, name });
}
if you dispose your connection, you need dispose your command, calling Dispose on it will supress the call to the finalizer. Add using command after using conenction
Don't set your command before connection
Yes, because you close your not managed object , who is coonnection
Remark : using bloc is preferred that try catch finally for basic need without custom treatment in catch bloc
msdn sample link : http://msdn.microsoft.com/fr-fr/library/system.data.sqlclient.sqlconnection(v=vs.110).aspx
this article don't treat using command but speak about connection
What would happen if you call Close() on a SqlConnection object before you call Close() on a SqlDataReader using that connection?
Actually, what I really want to know is whether or not the order in which you Close them matters. Does calling SqlConnection.Close() completely close the connection, or will it remain open if you do not call Close() on a SqlDataReader using that connection?
Sorry for the multiple questions, but I don't think I really understand how connection closing works.
It'll close the connection (returns it to the pool) and SqlDataReader would throw an exception (System.InvalidOperationException) in case it's used afterward.
Rather than worrying about the order on how to close them, why not wrap them in using statements.
// the following code has parts left out for brevity...
using(var conn = new SqlConnection( ... ))
using(var cmd = new SqlCommand( ... ))
{
conn.Open();
using(var reader = cmd.ExecuteReader())
{
// do whatever with the reader here...
}
}
the using statements ensure that your objects are closed, and in the correct order if you nest them accordingly. See http://msdn.microsoft.com/en-us/library/yh598w02.aspx for more info.
The actual database connection will be closed (returned to the pool) when you close/dispose the SqlConnection object, so the database resources are safe.
However, you should close/dispose the SqlDataReader also, otherwise it will keep a reference to the SqlConnection object, keeping them both in memory. Eventually the finalizer will dispose the SqlDataReader object if you don't do it, and then the SqlConnection object can also be collected, but you have no control over when that happens.
The SqlDataReader can be partially usable after you have closed the connection, but nothing that you really can rely on. It still has some data in it's buffer, so some operations may work, but anything that requires more data from the database will cause an exception.
I use a pattern that looks something like this often. I'm wondering if this is alright or if there is a best practice that I am not applying here.
Specifically I'm wondering; in the case that an exception is thrown is the code that I have in the finally block enough to ensure that the connection is closed appropriately?
public class SomeDataClass : IDisposable
{
private SqlConnection _conn;
//constructors and methods
private DoSomethingWithTheSqlConnection()
{
//some code excluded for brevity
try
{
using (SqlCommand cmd = new SqlCommand(SqlQuery.CountSomething, _SqlConnection))
{
_SqlConnection.Open();
countOfSomething = Convert.ToInt32(cmd.ExecuteScalar());
}
}
finally
{
//is this the best way?
if (_SqlConnection.State == ConnectionState.Closed)
_SqlConnection.Close();
}
//some code excluded for brevity
}
public Dispose()
{
_conn.Dispose();
}
}
Wrap your database handling code inside a "using"
using (SqlConnection conn = new SqlConnection (...))
{
// Whatever happens in here, the connection is
// disposed of (closed) at the end.
}
The .Net Framework mantains a connection pool for a reason. Trust it! :)
You don't have to write so much code just to connect to the database and release the connection.
You can just use the 'using' statement and rest assured that 'IDBConnection.Release()' will close the connection for you.
Highly elaborate 'solutions' tend to result in buggy code. Simple is better.
MSDN Docs make this pretty clear...
The Close method rolls back any pending transactions. It then releases the connection to the connection pool, or closes the connection if connection pooling is disabled.
You probably haven't (and don't want to) disable connection pooling, so the pool ultimately manages the state of the connection after you call "Close". This could be important as you may be confused looking from the database server side at all the open connections.
An application can call Close more than one time. No exception is generated.
So why bother testing for Closed? Just call Close().
Close and Dispose are functionally equivalent.
This is why a using block results in a closed connection. using calls Dispose for you.
Do not call Close or Dispose on a Connection, a DataReader, or any other managed object in the Finalize method of your class.
Important safety tip. Thanks, Egon.
I'm guessing that by _SqlConnection.State == ConnectionState.Closed you meant !=
This will certainly work. I think it is more customary to contain the connection object itself inside a using statement, but what you have is good if you want to reuse the same connection object for some reason.
One thing that you should definitely change, though, is the Dispose() method. You should not reference the connection object in dispose, because it may have already been finalized at that point. You should follow the recommended Dispose pattern instead.
Since you're using IDisposables anyway. You can use the 'using' keyword, which is basically equivalent to calling dispose in a finally block, but it looks better.
See this question for the answer:
Close and Dispose - which to call?
If your connection lifetime is a single method call, use the using feature of the language to ensure the proper clean-up of the connection. While a try/finally block is functionally the same, it requires more code and IMO is less readable. There is no need to check the state of the connection, you can call Dispose regardless and it will handle cleaning-up the connection.
If your connection lifetime corresponds to the lifetime of a containing class, then implement IDisposable and clean-up the connection in Dispose.
Put the connection close code inside a "Finally" block like you show. Finally blocks are executed before the exception is thrown. Using a "using" block works just as well, but I find the explicit "Finally" method more clear.
Using statements are old hat to many developers, but younger developers might not know that off hand.
no need for a try..finally around a "using", the using IS a try..finally
Might I suggest this:
class SqlOpener : IDisposable
{
SqlConnection _connection;
public SqlOpener(SqlConnection connection)
{
_connection = connection;
_connection.Open();
}
void IDisposable.Dispose()
{
_connection.Close();
}
}
public class SomeDataClass : IDisposable
{
private SqlConnection _conn;
//constructors and methods
private void DoSomethingWithTheSqlConnection()
{
//some code excluded for brevity
using (SqlCommand cmd = new SqlCommand("some sql query", _conn))
using(new SqlOpener(_conn))
{
int countOfSomething = Convert.ToInt32(cmd.ExecuteScalar());
}
//some code excluded for brevity
}
public void Dispose()
{
_conn.Dispose();
}
}
Hope that helps :)