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When does EF Core DBContext dispose Sql Connection?

When using classic ADO.NET we typically close the SQL connection as soon as we are done executing the SQL command, so the connection is closed and returned back to the pool.
Something like:
public Order[] GetActiveOrders()
{
var orders = new List<Orders>();
using (SqlConnection connection = new SqlConnection("connectionString"))
{
using (SqlCommand cmd = connection.CreateCommand())
{
cmd.CommandType = System.Data.CommandType.Text;
cmd.CommandText = "Select * FROM ORDERS WHERE Status = 'Active'";
cmd.Connection.Open();
using (var reader = cmd.ExecuteReader())
{
//populate orders
}
}
}
// SQL connection is closed here and returned back to connection pool
return orders;
}
In ASP.NET Core using EF Core, we typically inject the DbContext into constructor using DI framework
public class OrderService:IDisposable
{
private readonly MyDBContext _dbContext;
public OrderService(MyDBContext dbContext)
{
_dbContext = dbContext;
}
public Order[] GetActiveOrders()
{
var orders = _dbContext.Orders.Where(x=>x.Status == 'Active').ToArray()
return orders;
}
#region Dispose
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (_disposed)
return;
if (disposing)
{
if (_dbContext != null)
{
_dbContext.Dispose();
}
// Free any other managed objects here.
}
// Free any unmanaged objects here.
_disposed = true;
}
}
I am assuming under the hood, the DbContext is still using SqlCommand and SqlConnection to connect to the database.
I want to know when does EF Core close the SqlConnection? Does it close the connection as soon as it's done executing the query (like how we do in classic ADO) or when the DbContext is disposed?
So in the example above, will it dispose the connection before returning Orders from the GetActiveOrders() method or when the OrderService is disposed by the DI container?

Side note: you shouldn't dispose something you don't own, which is the case with DI injected DbContext (and any injected object).
But to answer you concrete question. I can't find documentation to link to, but as soon as you
don't provide pre allocated DbConnection object via DbContextOptions
don't manually open connection via .Database.OpenConnection method
don't open explicit transactions via Database.BeginTransaction method
i.e. do not take some connection management by yourself (in which case you are responsible for closing/disposing), EF Core opens connection only when needed and closes it immediately after that.
When needed means opening a transaction during the SaveChanges until it gets commit or rolled back. Or when executing DbReader returning query until the returned reader is consumed or cancelled. In other words, exactly how you would do it with classic ADO.NET. And yes, behind the scenes it uses ADO.NET (at least for relational databases).
Some additional info here Do I need to close the DbConnection manually when using ambient transactions with EF Core 2.1? and Using EF Core to invoke stored procedure and closing connection. Also Connection Resiliency and How queries work documentation topics.

Making a data access class for all programs or individual C#

So the title is a bit vague, but the question is really this: in practice is it best to make a data access class, in this case access to a SQL Server.
Where all the static methods of the class need a connection string and a SQL statement?
Something along these lines:
public static void ExecuteSql(string connStr, string strSqlStatement)
{
SqlConnection conn = new SqlConnection(connStr);
conn.Open();
SqlCommand cmd = new SqlCommand(strSqlStatement, conn);
cmd.ExecuteNonQuery();
conn.Close();
conn.Dispose();
}
And then a method that does something similar except it returns data you queried for.
Or in practice, is it better to create an object for the specific application you are building, and code these items as the objects extensions. So the SQL to run or stored procedure to execute would be wrapped up in that class.
obj.GetSomethingViaQueryThatIsWrittenInTheClassLibrary()
So I guess the first one is more like a service library for accessing and writing data in a SQL Server database. What does one typically do in this situation?
Or could you even use the service library in tandem with the objects library?
There's a ton of, not conflicting, but different opinions on data access and I am really trying to see what is more common a practice.

I disagree with Terry, because:
The connections are pooled, so opening/closing connections is not a problem and you don't want to use a single connection to execute multiple concurrent queries. This is very usefull when having many concurrent threads (for example webservers) but this also applies on a normal application (which might uses Tasks to retrieve data on a separate thread to keep the UI responsive)
So I would create a ConnectionManager class that uses a connection string as constructor parameter, this way the connectionstring wouldn't 'travel' thru your program and is encapsulated in a 'manager' object.
This is a poor example, but I think it work just fine when using ADO.NET
public class ConnectionManager
{
private string _connectionString;
public ConnectionManager(string connectionString)
{
_connectionString = connectionString;
}
public SqlConnection GetConnection()
{
return new SqlConnection(_connectionString);
}
}
Then I would use it something like:
var connectionManager = new ConnectionManager(connectionString);
using(var con = connectionManager.GetConnection())
{
// not all operations require .Open()/.Close()
// multiple queries.
}
using(var con = connectionManager.GetConnection())
{
// not all operations require .Open()/.Close()
// multiple other queries.
}
By using using the connection will be disposed (put back in the pool)
You might even use something like:
public class ConnectionManager
{
private string _connectionString;
public ConnectionManager(string connectionString)
{
_connectionString = connectionString;
}
public void ExecuteNonQuery(string strSqlStatement)
{
using(var connection = new SqlConnection(_connectionString))
using(var command = new SqlCommand(strSqlStatement, connection))
{
connection.Open();
command.ExecuteNonQuery();
}
}
}
Which makes:
var connectionManager = new ConnectionManager(connectionString);
connectionManager.ExecuteNonQuery("SELECT * FROM Whatever");
Tip: You sure need to checkout the SqlParameter to prevent SQL Injection

I wouldn't create, open, and close the connection in an sql execute method like that. Instead, I recommend creating the connection and pass it in to the query method each time a query is needed and when all queries are finished, then close the connection.

Managing and Closing Dynamically created SQL connections in .net

I have a c# windows form application that connects to databases dynamically where each user may connect to different databases.
The current implementation is as follows:
Connection Repository that contains a dynamically populated list of connections (per user).
When a user initiates a request that requires a database connection the respective connection is looked up from the connection repository ,opened , and then used in the user request .
Code Sample from the connection repository
public class RepoItem
{
public string databasename;
public SqlConnection sqlcnn;
}
public class ConnectionRepository
{
private List<RepoItem> connectionrepositroylist;
public SqlConnection getConnection(String dbname)
{
SqlConnection cnn = (from n in connectionrepositroylist
where n.databasename == dbname
select n.sqlcnn).Single;
cnn.Open();
return cnn;
}
}
sorry for any code errors i just improvised a small version of the implementation for demonstration purpose.
I'am not closing connections after a command execution because it may be used by another command simultaneously.
The questions are:
Should i be worried about closing the connections ?
Does connection close automatically if it is idle for a specific period ?
I have a method in mind to implement a timer in the created Connection Repository and check for idle connections through the Executing ConnectionState Enumeration and close them manually.
Any suggestions are welcome .
When i want a specific connection i call the getConnection function in the ConnectionRepository class and pass the database name as a parameter.
PS: I didn't post the complete implemented code because it is quite big and includes the preferences that affect the populating of the connection list.

I would suggest not to return the SQLConnection to the calling method at all.
Instead, create a method that will accept an Action<SqlConnection>, create the connection inside a using block, and execute the action inside that block
This way you know that the connection will always be correctly closed and disposed, while giving the using code the freedom to do whatever it needs:
public class RepoItem
{
public string databasename;
public SqlConnection sqlcnn;
}
public class DatabaseConnector
{
private List<RepoItem> connectionrepositroylist;
private SqlConnection GetConnection(String dbname)
{
return (from n in connectionrepositroylist
where n.databasename == dbname
select n.sqlcnn).SingleOrDefault();
}
public void Execute(String dbname, Action<SqlConnection> action)
{
using (var cnn = GetConnection(dbname))
{
if (cnn != null) // in case dbname is not in the list...
{
cnn.Open();
action(cnn);
}
}
}
}
Then, to execute an sql statement you can do something like this:
public void ExecuteReaderExample(string dbName, string sql)
{
Execute("dbName",
connection =>
{
using (var cmd = new SqlCommand(sql, connection))
{
using (var reader = cmd.ExecuteReader())
{
while (reader.Read())
{
// do stuff with data form the database
}
}
}
});
}
Of course, you can also wrap the SqlCommand in a method like this.
I've been working with this approach for quite some time now, and as far as I can tell it's working well. In fact, It's working so well I've published a project on git hub based on this approach.
It saves you a lot of the plumbing when dealing with ado.net, by wrapping the connection, command, reader and adapter much the same way.
Feel free to download it and adapt to your needs.
P.S.
To answer your questions directly:
Should i be worried about closing the connections ?
Yes, you should.
Does connection close automatically if it is idle for a specific period ?
No, it doesn't.
However, implementing a method like I suggested will handle closing and disposing the connection object for you, so you don't need to worry about it.
Update
As Yahfoufi wrote in his comment, this design has a flaw, since multiple commands are using the same instance of SqlConnection, you are risking closing the connection while other commands are running.
However, fixing this design flaw is very easy - instead of holding SqlConnection in RepoItem you can simply hold the connection string:
public class RepoItem
{
public string DatabaseName {get; set;}
public string ConnectionString {get; set;}
}
Then you change the GetConnection method like this:
private SqlConnection GetConnection(String dbname)
{
return new SqlConnection(from n in connectionrepositroylist
where n.databasename == dbname
select n.sqlcnn).SingleOrDefault());
}
Now each Execute method is working on it's own individual instance of SqlConnection so you don't need to worry about closing in the middle of some other command executing.
However, While we are on the subject of refactoring, I would suggest removing the RepoItem class all together and instead of using a List<RepoItem> to hold the connection strings simply use a Dictionary<string, string>, where the database name is the key and the connection string is the value. This way you can only have one connection string per database name, and your GetConnection method is simplified to this:
private Dictionary<string, string> connectionrepositroylist;
private string GetConnectionString(String dbname)
{
return connectionrepositroylist.ContainsKey(dbname) ? connectionrepositroylist[dbname] : "";
}
So, the complete DatabaseConnector class will look like this:
public class DatabaseConnector
{
private Dictionary<string, string> connectionrepositroylist;
private string GetConnectionString(String dbname)
{
return connectionrepositroylist.ContainsKey(dbname) ? connectionrepositroylist[dbname] : "";
}
public void Execute(String dbname, Action<SqlConnection> action)
{
var connectionString = GetConnectionString(dbname);
if(!string.IsNullOrEmpty(connectionString))
{
using (var cnn = new SqlConnection(connectionString))
{
cnn.Open();
action(cnn);
}
}
}
// Of course, You will need a way to populate your dictionary -
// I suggest having a couple of methods like this to add, update and remove items.
public bool AddOrUpdateDataBaseName(string dbname, string connectionString)
{
if(connectionrepositroylist.ContainsKey(dbname))
{
connectionrepositroylist[dbname] = connectionString;
}
else
{
connectionrepositroylist.Add(dbname, connectionString);
}
}
}

The good news is that ADO.Net manages your connection pools dynamically, so there's minimal overhead in you dynamically opening and closing connections in code. There's a good document here if you want to look through the detail.
To answer the specific questions you've raised:
Should i be worried about closing the connections ?
Yes, but not for the reasons you may think. Microsoft encourage you to close your connections, so as to return them to the pool for (re)use elsewhere in your code. Closing the connection doesn't actually close it - it merely returns the underlying connection to the pool. Failure to close your connections properly can lead to delays in them being returned to the pool, thus adversely affecting your applications performance as more connections need to be added to the pool to cope with demand.
Does connection close automatically if it is idle for a specific
period ?
A connection is only returned to the pool when it's Dispose or Finalise methods get called. If you create a connection and drop it into a static container then it will not be returned to the pool at all. As such, your ConnectionRepository may actually be harming performance.
I have a method in mind to implement a timer in the created Connection
Repository and check for idle connections
This is unnecessary - close your connections to allow them to return to the pool. This way they will be available for other threads to use
Personally, I'd suggest that you modify your RepoItem class to store connection strings, rather than connection objects, and let ADO.Net's pooling do all the heavy lifting.
public static class ConnectionRepository
{
private static readonly Dictionary<string, string> Connections = new Dictionary<string, string>(StringComparer.CurrentCultureIgnoreCase);
public static bool Contains(string key)
{
return Connections.ContainsKey(key);
}
public static void Add(string key, string connectionString)
{
Connections.Add(key, connectionString);
}
public static SqlConnection Get(string key)
{
var con = new SqlConnection(Connections[key]);
con.Open();
return con;
}
}
With this in place, you can query the database as follows:
public static void foo()
{
using (var con = ConnectionRepository.Get("MyConnection"))
using (var cmd = new SqlCommand("SELECT * FROM MyTable", con))
{
var dr = cmd.ExecuteReader();
//...
}
}
Once the query has executed and the connection is no longer required, the using() block calls its Dispose() method and releases the underlying connection back to the pool for re-use.

As #tinudu says, the SqlConnection class reuses existing connections automatically - you don't have to implement that yourself. See SQL Server Connection Pooling.
If you create the SqlConnection object in a using statement, C# will close the connection automatically as required.
Wrapping the whole thing (create connection, open, run query, close connection) in a function is the best idea. You can put the function in a repository base-class, so it is available to all your repositories.
You would need several functions for the different types of SQL query (select, update, stored proc) but you only need to write one of each - they will get reused.

if you worried about so many conditions let say parallel execution as
well so consider reserving connections for app and close all at once
when app is closing.
public class RepoItem
{
public string databasename;
public SqlConnection sqlcnn;
}
public class ConnectionRepository
{
private List<RepoItem> connectionrepositroylist;
public SqlConnection getConnection(String dbname)
{
SqlConnection cnn = (from n in connectionrepositroylist
where n.databasename == dbname
select n.sqlcnn).Single;
if (cnn!= null && cnn.State == cnn.Closed) // Impelement other checks as well
{
cnn.Open();
}
return cnn;
}
}
Implement CloseConnections and call while application closing i.e
Application.ApplicationExit event
public void CloseConnections()
{
foreach (var connection in connectionrepositroylist)
{
try
{
if (connection.State == System.Data.ConnectionState.Open) // check other conditions
{
connection.Close();
}
}
catch (Exception)
{
//logging or special handling
}
}
}
Points to be note
If some query is still executing and user tries to shut down or close the
app can consider following implementations
Wont allow the application shutdown . Callback delegate will help in this
case to ensure that query is returned.
Force stop and close the connection

It is a better Practice to close the sqlconnection manually, Since it can release the connection which can be used for other processes. Also note that you should open the connection as much as late you can and close it early as possible.

Correctly reusing SqlCommand and SqlParameter whilst pooling the connection

I am working on a setup where a scalable WCF Service Component is connected to a single MS SQL Server Database. The RESTful service allows users to save data into the DB as well as get data from it.
Whilst implementing a class handling the database connections / methods, I started struggling with correctly reusing prepared SqlCommands and the connection. I read up on the MSDN about connection pooling as well as how to use SqlCommand and SqlParameter.
My initial version of the class looks like this:
public class SqlRepository : IDisposable
{
private object syncRoot = new object();
private SqlConnection connection;
private SqlCommand saveDataCommand;
private SqlCommand getDataCommand;
public SqlRepository(string connectionString)
{
// establish sql connection
connection = new SqlConnection(connectionString);
connection.Open();
// save data
saveDataCommand = new SqlCommand("INSERT INTO Table (Operation, CustomerId, Data, DataId, CreationDate, ExpirationDate) VALUES (#Operation, #CustomerId, #Data, #DataId, #CreationDate, #ExpirationDate)", connection);
saveDataCommand.Parameters.Add(new SqlParameter("Operation", SqlDbType.NVarChar, 20));
saveDataCommand.Parameters.Add(new SqlParameter("CustomerId", SqlDbType.NVarChar, 50));
saveDataCommand.Parameters.Add(new SqlParameter("Data", SqlDbType.NVarChar, 50));
saveDataCommand.Parameters.Add(new SqlParameter("DataId", SqlDbType.NVarChar, 50));
saveDataCommand.Parameters.Add(new SqlParameter("CreationDate", SqlDbType.DateTime));
saveDataCommand.Parameters.Add(new SqlParameter("ExpirationDate", SqlDbType.DateTime));
saveDataCommand.Prepare();
// get data
getTripCommand = new SqlCommand("SELECT TOP 1 Data FROM Table WHERE CustomerId = #CustomerId AND DataId = #DataId AND ExpirationDate > #ExpirationDate ORDER BY CreationDate DESC", connection);
getTripCommand.Parameters.Add(new SqlParameter("CustomerId", SqlDbType.NVarChar, 50));
getTripCommand.Parameters.Add(new SqlParameter("DataId", SqlDbType.NVarChar, 50));
getTripCommand.Parameters.Add(new SqlParameter("ExpirationDate", SqlDbType.DateTime));
getTripCommand.Prepare();
}
public void SaveData(string customerId, string dataId, string operation, string data, DateTime expirationDate)
{
lock (syncRoot)
{
saveDataCommand.Parameters["Operation"].Value = operation;
saveDataCommand.Parameters["CustomerId"].Value = customerId;
saveDataCommand.Parameters["CreationDate"].Value = DateTime.UtcNow;
saveDataCommand.Parameters["ExpirationDate"].Value = expirationDate;
saveDataCommand.Parameters["Data"].Value = data;
saveDataCommand.Parameters["DataId"].Value = dataId;
saveDataCommand.ExecuteNonQuery();
}
}
public string GetData(string customerId, string dataId)
{
lock (syncRoot)
{
getDataCommand.Parameters["CustomerId"].Value = customerId;
getDataCommand.Parameters["DataId"].Value = dataId;
getDataCommand.Parameters["ExpirationDate"].Value = DateTime.UtcNow;
using (var reader = getDataCommand.ExecuteReader())
{
if (reader.Read())
{
string data = reader.GetFieldValue<string>(0);
return data;
}
else
{
return null;
}
}
}
}
public void Dispose()
{
try
{
if (connection != null)
{
connection.Close();
connection.Dispose();
}
DisposeCommand(saveDataCommand);
DisposeCommand(getDataCommand);
}
catch { }
}
private void DisposeCommand(SqlCommand command)
{
try
{
command.Dispose();
}
catch (Exception)
{
}
}
}
There are several aspects important to know:
I am using SqlCommand.Prepare() to speed up the process of executing the command
Reusing the commands avoids creating new objects with every call to the GetData and SaveData methods, thus leading to no problem with the garbage collector
There is only one instance of the SqlRepository class, used by the WCF Service.
There are many many calls per minute to this service, so keeping a connection to the DB open is what I want.
Now I read up a bit more about connection pooling and the fact that it is highly recommended to use the SqlConnection object in a using statement to ensure disposal. To my understanding, the connection pooling technology takes care of leaving the connection open even though the Dispose() method of SqlConnection has been called by the using statement.
The way to use this would be to have a using(SqlConnection connection = new SqlConnection(connectionString)) inside the GetData and SaveData methods. However, then - at least to my intuition - I would need to create the SqlCommands inside the GetData / SaveData methods as well. Or not? I could not find any documentation on how to reuse the commands that way. Also wouldn't the call to SqlCommand.Prepare() be meaningless if I need to prepare a new command every time I get into the GetData / SaveData methods?
How do I properly implement the SqlRepository class? The way it is now I believe that if the connection breaks (maybe because the DB server goes down for a while and reboots), then the SqlRepository class will not automatically recover and be functioning. To my best knowledge this sort of failsave scenarios are handled in the pooling technology.
Thanks for ideas and feedback!
Christian

Do not reuse the SqlCommand instances.
You are synchronizing database access.
With your implementation, you are re-using a small object (which is no problem for the GC even if there are thousands) in exchange of concurrent DB operations.
Remove the synchronization locks.
Create new instances of SqlCommands for each database operation.
Do not call Prepare. Prepare speeds up db operations, but after executing ExecuteReader() on a SqlCommand with CommandType = Text and with non-zero number of parameters, the command is unprepared internally.

C#.net lock object in one mthod and no lock in another method

I have two method “ExecuteNoQuery” (performs dbCommand.ExecuteNonQuery()) and “Query” performs (dbCommand.ExecuteReader()).
Both the methods are using same connection object. In ExecuteNoQuery method a lock is implemented(using connection object) and Query method implemented with out lock. In case of multiple thred, different thread accessing both the method simultaneously then what will happen?
Note: In Query method custom connection pooling is implemented with the same object.
public int ExecuteNoQuery(string sqlquery, Hashtable htData) {
try {
lock(Myservice.dbcon)
{
using (OracleCommand dbCommand = new OracleCommand(sqlquery, Myservice.dbcon))
{
int rowCount = dbCommand.ExecuteNonQuery();
return 1;
}
}
}
public OracleDataReader Query(string sqlquery, Hashtable htData)
{
try
{
OracleDataReader dbReader = null;
Random ran = new Random();
int randomnumber = ran.Next(1,5);
Myservice.dbcon = (OracleConnection) Myservice.htdbcon
["Connection_" +randomnumber];
if (Myservice.dbcon.State != System.Data.ConnectionState.Executing
|| Myservice.dbcon != System.Data.ConnectionState.Fetching)
{
using (OracleCommand dbCommand = new OracleCommand(sqlquery,
Myservice.dbcon))
{
dbReader = dbCommand.ExecuteReader();
}
}
return dbReader;
}

Both the methods are using same connection object.
Since one method uses a lock and the other does not: bad things. No guarantees are made by the object for this scenario, so you should expect it to fail in interesting ways. You should use the same lock object from both places, or better: only use a connection in isolated code, not a shared connection. With connection pooling, it is very rarely useful to have a shared connection object somewhere. A far more suitable pattern is usually to obtain a connection when you need it, and then dispose it. If the underlying provider supports pooling, this will perform ideally, without any issues of synchronization, and will allow parallel queries etc. For example:
using (var conn = SomeUtilityClass.GetOpenConnection())
using (var cmd = conn.CreateCommand())
{
cmd.CommandText = sqlquery;
int rowCount = dbCommand.ExecuteNonQuery();
return 1;
}
and, importantly, do the same from the Query method; no locks, no global shared connections.
I'd also be concerned by the lack of parameters, btw. That suggests you are opening yourself up to SQL injection errors.