I usually use code like this:
using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["MyConn"].ConnectionString))
{
var command = connection.CreateCommand();
command.CommandText = "...";
connection.Open();
command.ExecuteNonQuery();
}
Will my command automatically disposed? Or not and I have to wrap it into using block? Is it required to dispose SqlCommand?
Just do this:
using(var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["MyConn"].ConnectionString))
using(var command = connection.CreateCommand())
{
command.CommandText = "...";
connection.Open();
command.ExecuteNonQuery();
}
Not calling dispose on the command won't do anything too bad. However, calling Dispose on it will suppress the call to the finalizer, making calling dispose a performance enhancement.
The safest policy is to always call Dispose() on an object if it implements IDisposable, either explicitly or via a using block. There may be cases where it is not required but calling it anyway should never cause problems (if the class is written correctly). Also, you never know when an implementation may change meaning that where the call was previously not required it is now definitely required.
In the example you've given, you can add an extra inner using block for the command, as well as maintaining the outer using block for the connection.
Yes, you should, even if it the implementation is currently not doing much, you don't know how it is going to be changed in the future (newer framework versions for instance). In general, you should dispose all objects which implement IDisposable to be on the safe side.
However, if the operation is deferred and you don't control the full scope (for instance when working asynchroneously, or when returning an SqlDataReader or so), you can set the CommandBehavior to CloseConnection so that as soon as the reader is done, the connection is properly closed/disposed for you.
In practice, you can skip Dispose. It doesn't free any resources. It doesn't even suppress finalization since the SQLCommand constructor does that.
In theory, Microsoft could change the implementation to hold an unmanaged resource, but I would hope they'd come out with an API that gets rid of the Component base class long before they'd do that.
You can find out this kind of stuff using Reflector or dotPeek or https://referencesource.microsoft.com/.
I had a small dig (I would suggest that you dig yourself though to be fully sure of the rest of this though as I didn't try that hard) and it looks like when you kill a connection there is no disposal of any children associated with that connection. Furthermore it doesn't actually look like the disposal of a command actually does that much. It will set a field to null, detach itself from a container (this may prevent a managed memory leak) and raise an event (this might be important but I can't see who is listening to this event).
Either way it's good practice to use this stuff in a using block or to ensure you dispose of it using a dispose pattern in the object that holds the connection (if you intend to hold onto the command for a while).
In my opinion, calling Dispose for both SqlConnection and SqlCommand is good practice, use below code
using(var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["MyConn"].ConnectionString))
try{
using(var command = connection.CreateCommand())
{
command.CommandText = "...";
connection.Open();
command.ExecuteNonQuery();
}
}
catch(Exception ex){ //Log exception according to your own way
throw;
}
finally{
command.Dispose();
connection.Close();
connection.Dispose();
}
Related
I am the third generation to work on a system within my organization and of course there are differences in programming styles. I was wondering what the correct way of connecting to a database is as there are two different styles being used within the system. So whats the "correct" way?
Method 1:
try
{
using (SqlConnection con = new SqlConnection(connectionString))
{
con.Open();
using (SqlCommand command = new SqlCommand("StoredProcedure", con))
{
command.CommandType = CommandType.StoredProcedure;
command.Parameters.Add(new SqlParameter("foo", bar));
}
using (SqlDataReader reader = command.ExecuteReader())
{
//do stuff
}
}
}
catch (Exception ex)
{
//do stuff
}
Method 2:
// Variables
SqlCommand loComm;
SqlConnection loConn = null;
SqlDataReader loDR;
try
{
// Init command
loComm = new SqlCommand("foo");
loComm.CommandType = CommandType.StoredProcedure;
loComm.Parameters.AddWithValue("foo", bar);
// Init conn
loConn = new SqlConnection(String);
loConn.Open();
loComm.Connection = loConn;
// Run command
loDR = loComm.ExecuteReader();
//do stuff
}
catch (Exception ex)
{
//do stuff
}
While both methods work I am not sure which one is the most appropriate to use. Is there a reason to use one over the other? The second method is cleaner and easier to understand to me, but it doesn't automatically run the iDispose() function when it is finished.
Edit: My question is different then the one suggested, because one approach uses the "using" statement while the other doesn't. So my question is directly related to whether or not to utilize the "using" statements when making a database connection.
Thanks, for all the responses.
Method 2 is simply incorrect and should be repaired.
When completed, you will be left with IDisposable instances that have not been disposed. Most likely, this will play havoc with the connection management that goes on behind the scenes with SqlConnection, especially if this code gets thrashed a lot before GC decides to step in.
If an instance is IDisposable, then it needs to be Disposed of, preferably in the smallest scope possible. Using using will ensure that this happens, even if the code malfunctions and exceptions are thrown.
A using statement:
using(var disposableInstance = new SomeDisposableClass())
{
//use your disposable instance
}
is (give or take a few minor details) syntactic sugar for:
var disposableInstance = new SomeDisposableClass();
try
{
//use your disposable instance
}
finally
{
//this will definitely run, even if there are exceptions in the try block
disposableInstance.Dispose();
}
Even if something goes wrong in the try block, you can be assured that the finally block will execute, thereby ensuring that your disposables are disposed, no matter what happens.
In the first example, if there is an exception thrown, the objects wrapped in the using blocks will be properly closed and disposed.
In the second, you will manually need to dispose of your objects.
One other thing worth mentioning is that if you were planning on disposing of your objects only when an exception is thrown, you will have objects that are not disposed of, so you would need to implement a try..catch..finally and dispose the objects within the finally block.
The first is the better option.
The first one will close the connection if an exception is thrown.
The second one won't, so I'd say go with the first choice.
What the using block does is to warranty that the object Dispose method will always be invoked, no matter if an exception is thrown or not.
Dispose is a method used to clean up resources. In the case of a DB connection, the connection is released, which is really important.
So, the correct way in this case is using the using pattern.
The object included between the using parents mus be IDisposable whic means that it has a Dispose method that should be invoked when the object is no longer needed. If you don't invoke dispose, it will be disposde at any indeterminate time, when the garbage collector destroys the object. That's undesirable in case like a DB connection that must be closed as soon as possible.
The equivalen of usin is a try finally, which includes a call to Dispose within the finally block.
Reading here, it says:
As a rule, when you use an IDisposable object, you should declare and instantiate it in a using statement. The using statement calls the Dispose method on the object in the correct way, and (when you use it as shown earlier) it also causes the object itself to go out of scope as soon as Dispose is called. Within the using block, the object is read-only and cannot be modified or reassigned. The using statement ensures that Dispose is called even if an exception occurs while you are calling methods on the object. You can achieve the same result by putting the object inside a try block and then calling Dispose in a finally block; in fact, this is how the using statement is translated by the compiler.
That sounds like the correct way is method 1.
I am a developer that is maintaining and constantly making an application faster and better. I came across a piece of code that uses .Dispose(), which is inside a using statement.
Here is the code:
using (IDbCommand cmd = proxy.Connection.CreateCommand())
{
cmd.CommandText = "usp_GetPluginInfo";
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add(proxy.Connection.CreateParameter(cmd, "#dealershipId", dealershipId));
cmd.Parameters.Add(proxy.Connection.CreateParameter(cmd, "#pluginId", pluginId));
PluginInfo[] pluginInfos = PopulatePluginsFromCommand(cmd);
result = pluginInfos.First();
cmd.Dispose();
}
Wouldn't the last } Dispose when the Command is finished? I didn't think that it was necessary to use Dispose() in this case.
Thanks for all of your help!
You're right, it's not necessary.
A using statement is translated by the compiler to this:
IDbCommand cmd = proxy.Connection.CreateCommand();
try
{
//...
}
finally
{
if(cmd != null)
((IDisposable)cmd).Dispose();
}
Having said that, calling Dispose more than once should not be "hurtful" either, as a proper IDisposable implementation is supposed to be idempotent. It is, however, redundant, and you should remove it, since you're cleaning up the code.
You are correct! The using block is syntactic sugar for the following:
IDbCommand cmd = proxy.Connection.CreateCommand();
try
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add(proxy.Connection.CreateParameter(cmd, "#dealershipId", dealershipId));
cmd.Parameters.Add(proxy.Connection.CreateParameter(cmd, "#pluginId", pluginId));
PluginInfo[] pluginInfos = PopulatePluginsFromCommand(cmd);
result = pluginInfos.First();}
finally
{
if(cmd != null)
{
((IDisposable)cmd).Dispose();
}
}
So yes, the extra cmd.Dispose(); is unnecessary. In most cases, a well-written class will do nothing the second .Dispose() (using the so-called Disposable Pattern), but sometimes it will cause issues. Get rid of it!
using statement always calls IDisposable.Dispose() method. cmb.Dispose() code is redundant
using calls Dispose upon exit of the block, no matter whether the block is run successfully or an exception occurs. In your example, the explicit call to Dispose is redundant.
There is one reason he could've put it there explicitly. If the IDbCommand isn't the one from System.Data, and the interface that was made for some reason inherited from IDisposable but used new instead of override, they could have different behaviours. But it's 99.999999999% of the time absolutely redundant.
It's redundant and the explicit call to Dispose is not guaranteed to execute. If you want to call Dispose explicitly make sure to do it in a finally block.
The cmd.Dispose(); is unnecessary. In a case where Dispose() is not properly implemented or made to throw the System.ObjectDisposedException, this could be an issue
Refer to the code analysis rule below
The call to CA2202: Do not dispose objects multiple times
I keep finding conflicting results for this question. Let's look at this C# code of running an SQL query:
using (SqlConnection cn = new SqlConnection(strConnectString))
{
cn.Open();
using (SqlCommand cmd = new SqlCommand(strSQL, cn))
{
cmd.ExecuteNonQuery();
}
//Do I need to call?
cn.Close();
}
Do I need to call that last cn.Close()? The reason I'm asking is that in a heavy traffic web app I run out of connections in a pool.
The using keyword as used here:
using (SqlConnection cn = new SqlConnection(strConnectString))
{
// Stuff
}
is short for:
SqlConnection cn = null;
try
{
cn = new SqlConnection(strConnectString);
// Stuff
}
finally
{
if (cn != null) cn.Dispose();
}
cn.Dispose() will be called immediately after cn goes out of scope of the using, which in turn immediately closes the connection (because SqlConnection.Dispose() does just that).
UPDATE
This should not be confused with garbage collection. GC is non-deterministic in .NET, which is exactly why the IDisposable inteface and Dispose Pattern were introduced. IDisposable allows expensive resources to be released in a timely, deterministic manner.
Not necessary to close it if you use using as it calls Displose() internally.
Here's a bit details about using keyword in ADO.NET, might be worth reading.
Leveraging the "using" keyword in C#
A quick search #SO will lead you to this post, where you can find your answers there too.
You dont need to close the connection when you use the Using statement.
Scott hanselman explains it here Why The Using Statement Is Better Than A Sharp Stick In The Eye And A SqlConnection Refactoring Example.
In a heavy traffic web app I run out of connections in a pool.
Make sure you are using the same connection string this way SQL will use Connection Pooling.
is the connection closed immediately, or is it closed when the garbage
collector gets to it
Edit:
The Dispose pattern is used to provide deterministic destruction of resources. Since the .net runtime garbage collector is non-deterministic (which means you can never be sure when the runtime will collect old objects and call their finalizer). Therefore, when you implement the Dispose pattern properly you provide deterministic release of the resources and in cases where the consumer is careless and does not dispose the object, the finalizer will clean up the object.
The database access classes that implement IDbConnection, IDbCommand and IDataReader all implement IDisposable, but obviously the Command and the Reader are dependent on the Connection. My question is, do I have to Dispose() of each these objects individually or will disposing of the Connection object dispose of the others too ?
That is, can I do this and guarantee I'm not risking leaving any unmanaged resources not being freed:
using (IDbConnection conn = GetConnection())
{
IDbCommand cmd = conn.CreateCommand();
cmd.CommandText = " ..... ";
IDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
}
}
Or do I have to do this instead:
using (IDbConnection conn = GetConnection())
{
using (IDbCommand cmd = conn.CreateCommand())
{
cmd.CommandText = " ..... ";
using (IDataReader rdr = cmd.ExecuteReader())
{
while (rdr.Read())
{
}
}
}
}
Or is this implementation dependent, so it would potentially work using one database's provider but not for another's ?
Best policy is to use all ADO.NET objects in using blocks- full stop.
A little Reflector-ing on various ADO.NET objects shows that things will more or less be dropped on the floor if not Closed/Disposed. The effect of that will depend a lot on which providers you're using- if you're using something with unmanaged handles underneath (ODBC, OleDb, etc), you're probably going to leak memory, as I didn't see anything in the way of finalizers. If it's an all-managed provider (eg, SqlClient), it'll eventually get cleaned up, but depending on which objects you're holding onto, you could end up keeping resources in use on the DB server a lot longer than you want.
You should dispose them individually or you could also use the solution provide here.
Dispose of them individually. It's entirely possible that the Reader and Command objects do more in their dispose routines than just destroy the connection (either now or in a future version of ADO.NET). So to (a) be explicit and (b) be safe you should dispose of them all individually.
The fact that they implement IDisposable suggests that you should always run the Dispose routine when you're finished with the object, so it's best not to try and second guess the interface, it won't give you any benefit, and you'll probably end up leaking memory and handles.
There are things you can do though to make your code look cleaner when nesting using statements. For example:
(using SqlConnection conn = new SqlConnection())
(using SqlCommand comm = new SqlCommand())
{
//Do stuff
}
That looks neater (in my opinion) than nesting braces.
You should dispose them individually. Even if disposing the IDbConnection would dispose everything under the covers (I don't know if it actually does, nor do I care, for the reason that follow), you should program in the future tense. Tomorrow somebody will edit that code and issue a new command on the same connection and then it will wonder why is he getting an error that the connection is still in use (because the IDataReader was no disposed).
The main advantage of the using statement is resources releasing management. Usually, the .NET Framework Garbage Collector controls resources allocation and release. With the using statement, we can take the control of it. So a using statement implements an IDisposible interface which contains a public Dispose() method.
Also you can always call a Dispose() method manually to release a resource or an object from memory.
hope this helps.
What is the proper way of closing a tread after running a query against a MySql database from a windows form in C#?
Is a simple open close enough like this?
conn.Open();
//querycode
conn.Close():
Try to use:
using(MySqlConnection conn = new MySqlConnection(connString))
{
conn.Open();
} // conn is automatically closed and disposed at the end of the using block
it is okay the way you are doing it, you can also wrap connection object into using block like this:
using (var con = new MySqlConnection(/*connection string*/))
{
con.Open();
//do stuff
// con.Close(); //don't need this it will be closed automatically*
}
(*see)
No, the code in your question is not good enough. If your query throws an exception you won't Close() it in a timely manner and it will be left hanging until the garbage collector notices it.
You need to enclose the object in a using block as shown by others or at a bare minimum encase it in a try/finally structure.
Classes that use resources that you need to clean up afterwards usually implement the IDisposable interface. This means it provides a function called Dispose() that can be used to free resources.
For disposable objects, you can use the using statement:
using ( SomeDisposableClass c = new SomeDisposableClass() ) {
// ... your code here
} // c.Dispose() automatically called here, freeing up resources
If the class is properly coded, it should free any resources -- be it a database connection, an opened file handle, etc -- in its Dispose() function.
This means that the MySQL probably disconnects from the database in Dispose(), so you probably don't need to explicitly call c.Close() -- but always check the documentation to be sure.