I've to create an embedded monitoring for existing application, these applications are using both Entity Framework and ADO. I have to check if the connections strings are good, and I'm doing it this way actually:
if (c.ConnectionString.Contains("metadata"))
{
using (var connection = new EntityConnection(c.ConnectionString))
{
try
{
connection.Open();
isWorking = true;
connection.Close();
}
catch (EntityException)
{
// Le catch n'a pas de raison d'être, la variable étant à false par défaut
}
}
}
else
{
using (var connection = new SqlConnection(c.ConnectionString))
{
try
{
connection.Open();
isWorking = true;
connection.Close();
}
catch (SqlException)
{
// Le catch n'a pas de raison d'être, la variable étant à false par défaut
}
}
}
But I've a lot of redundancy. How can I develop this thing to only got the try catch one time and not one for Entity an one for SQL ?
The connections strings are actually retrieved with System.Configuration.ConfigurationManager.ConnectionStrings
Thank you.
EntityConnection and SqlConnection both inherit from DbConnection as their common ancestor, so you can write a function that simply takes an instance of DbConnection and leave the rest of your code pretty much the same.
public bool CheckConnection(DbConnection connection)
{
try
{
connection.Open();
connection.Close();
return true;
}
catch (Exception)
{
// Le catch n'a pas de raison d'être, la variable étant à false par défaut.
}
return false;
}
You can then call your code using the same logic:
if (c.ConnectionString.Contains("metadata"))
{
using (var connection = new EntityConnection(c.ConnectionString))
{
isWorking = CheckConnection(connection);
}
}
else
{
using (var connection = new SqlConnection(c.ConnectionString))
{
isWorking = CheckConnection(connection);
}
}
This is just a simple refactoring using what you already have without changing the logic of your code.
If you don't want to catch the generic exception (which in my opinion is completely fine in this case), C# 6 offers a new construct to allow catching certain exceptions more generically:
catch (Exception ex) when (ex is EntityException || ex is SqlException)
{
// exception handling code
}
Also, if there is no additional logic in your if ... else statement, you can use a single using block:
if (c.ConnectionString.Contains("metadata"))
{
connection = new EntityConnection(c.ConnectionString);
}
else
{
connection = new SqlConnection(c.ConnectionString);
}
using (connection)
{
// same as before.
}
The next logical step would then be to make some sort of factory class / method that extracts and creates your different connections.
Since both are derived from DbConnection, you could do this:
using(DbConnection connection = c.ConnectionString.Contains("metadata") ?
new EntityConnection(c.ConnectionString) as DbConnection: new SqlConnection(c.ConnectionString) as DbConnection)
{
try
{
connection.Open();
isWorking = true;
connection.Close();
}
catch (Exception e) //make this more generic
{
//Do something
}
}
By making use of DbConnection (instead of individual Connection), you could test your connection.
Related
I have a android app created with xamarin.
This is the code that crashes, not the first time, but often on the second time!
public void InsertOrUpdateInventoryWithoutEntries(Inventory inventory)
{
_logger.Debug("Enter");
try
{
var db = _dataBaseConnection.GetSqLiteConnection();
using (db)
{
var existingDbInventory = db.Find<DbInventory>(dbInventory => dbInventory.Code ==
inventory.Code);
if (existingDbInventory != null)
{
if (!existingDbInventory.Finished ) // do not update if finished.
{
existingDbInventory.Description = inventory.Description;
existingDbInventory.OpenTime = inventory.OpenTime;
existingDbInventory.Finished = inventory.Finished ;
existingDbInventory.UseInventoryList = inventory.UseInventoryList;
existingDbInventory.PostedToServer = inventory.PostedToServer;
existingDbInventory.InventoryListIsDownloaded =
inventory.InventoryListIsDownloaded;
UpdateInventory(existingDbInventory,db);
}
}
else
{
db.Insert(DbInventory.FromInventory(inventory));
}
db.Close();
}
}
catch
(SQLiteException ex)
{
_logger.Error(ex);
throw;
}
}
private void UpdateInventory(DbInventory inventory, SQLiteConnection db)
{
_logger.Debug("Enter");
try
{
var result = db.Update(inventory);
}
catch (SQLiteException ex)
{
_logger.Error(ex);
throw;
}
}
public bool InsertOrUpdateInventoryEntry(InventoryEntry inventoryEntryModel,
SQLiteConnection db=null)
{
_logger.Debug("Enter");
bool disposeFlg = false;
//detta då sqllite inte klarar av samtidiga anrop så bra, så man skall bara använda en
connection i taget !
if (db == null)
{
db = _dataBaseConnection.GetSqLiteConnection();
disposeFlg = true;
}
var existingDbInvetoryRow = db.Find<DbInventoryEntry>(dbInventoryRow =>
dbInventoryRow.ItemId == inventoryEntryModel.ItemId && dbInventoryRow.InventoryCode ==
inventoryEntryModel.InventoryCode);
if (existingDbInvetoryRow != null)
{
existingDbInvetoryRow.Cost = inventoryEntryModel.Cost;
existingDbInvetoryRow.Quantity = inventoryEntryModel.Quantity;
db.Update(existingDbInvetoryRow);
}
else
{
db.Insert(DbInventoryEntry.FromInventoryEntry(inventoryEntryModel));
}
if (disposeFlg)
{
db.Close();
db.Dispose();
}
return true;
}
private bool InsertInventoryRows(IEnumerable<InventoryEntry> inventoryEntryModels)
{
_logger.Debug("Enter");
var dbRows = inventoryEntryModels.Select(entry =>
(DbInventoryEntry.FromInventoryEntry(entry)));
var db = _dataBaseConnection.GetSqLiteConnection();
using (db)
{
db.InsertAll(dbRows);
db.Close();
}
return true;
}
The error I get is:
SQLite.SQLiteException: 'database is locked' or SQLite.SQLiteException: 'database is busy'
I found the solution thanks to Jason - github.com/praeclarum/sqlite-net/issues/700
I would advise you to keep a single SQLiteConnection for your app and cache it to take advantage of the type mapping caching strategy. Opening it with the Create | ReadWrite | FullMutex flags will ensure all operations are multithread-wise serialized. Don't forget to Dispose the connection whenever your app closes
This worked perfectly and speeded up the app ! Thanks Jason !
What i did was to handle one static connection that i held open all the time !
So this is a little bit code-ceptionlike.
I have a function that is checking the last ID in a table, this function is called within another function. At the end of that function, I have another function that's opening another datareader.
Error:
There is already an open Datareader associated with this connection which must be closed first.
getLastIdfromDB()
public string getLastIdFromDB()
{
int lastIndex;
string lastID ="";
var dbCon = DB_connect.Instance();
if (dbCon.IsConnect())
{
MySqlCommand cmd2 = new MySqlCommand("SELECT ID FROM `competitor`", dbCon.Connection);
try
{
MySqlDataReader reader = cmd2.ExecuteReader();
while (reader.Read())
{
string item = reader2["ID"].ToString();
lastIndex = int.Parse(item);
lastIndex++;
lastID = lastIndex.ToString();
}
}
catch (Exception ex)
{
MessageBox.Show("Error:" + ex.Message);
}
}
return lastID;
}
This function is later-on used in this function:
private void addPlayerBtn_Click(object sender, EventArgs e)
{
ListViewItem lvi = new ListViewItem(getLastIdFromDB());
.........................................^
... HERE
...
... irrelevant code removed
.........................................
var dbCon = DB_connect.Instance();
if (dbCon.IsConnect())
{
MySqlCommand cmd = new MySqlCommand("INSERT INTO `competitor`(`ID`, `Name`, `Age`) VALUES(#idSql,#NameSql,#AgeSql)", dbCon.Connection);
cmd.Parameters.AddWithValue("#idSql", getLastIdFromDB());
cmd.Parameters.AddWithValue("#NameSql", playerName.Text);
cmd.Parameters.AddWithValue("#AgeSql", playerAge.Text);
try
{
cmd.ExecuteNonQuery();
listView1.Items.Clear();
}
catch (Exception ex)
{
MessageBox.Show("Error:" + ex.Message);
dbCon.Connection.Close();
}
finally
{
updateListView();
}
}
}
What would be the best way for me to solve this problem and in the future be sure to close my connections properly?
UPDATE: (per request, included DB_connect)
class DB_connect
{
private DB_connect()
{
}
private string databaseName = "simhopp";
public string DatabaseName
{
get { return databaseName; }
set { databaseName = value; }
}
public string Password { get; set; }
private MySqlConnection connection = null;
public MySqlConnection Connection
{
get { return connection; }
}
private static DB_connect _instance = null;
public static DB_connect Instance()
{
if (_instance == null)
_instance = new DB_connect();
return _instance;
}
public bool IsConnect()
{
bool result = true;
try
{
if (Connection == null)
{
if (String.IsNullOrEmpty(databaseName))
result = false;
string connstring = string.Format("Server=localhost; database={0}; UID=root;", databaseName);
connection = new MySqlConnection(connstring);
connection.Open();
result = true;
}
}
catch (Exception ex)
{
Console.Write("Error: " + ex.Message);
}
return result;
}
public void Close()
{
connection.Close();
}
}
}
You are trying to have multiple open readers on the same connection. This is commonly called "MARS" (multiple active result sets). MySql seems to have no support for it.
You will have to either limit yourself to one open reader at a time, or use more than one connection, so you can have one connection for each reader.
My suggestion would be to throw away that singleton-like thingy and instead use connection pooling and proper using blocks.
As suggested by Pikoh in the comments, using the using clause indeed solved it for me.
Working code-snippet:
getLastIdFromDB
using (MySqlDataReader reader2 = cmd2.ExecuteReader()) {
while (reader2.Read())
{
string item = reader2["ID"].ToString();
lastIndex = int.Parse(item);
lastIndex++;
lastID = lastIndex.ToString();
}
}
Your connection handling here is not good. You need to ditch the DB_connect. No need to maintain a single connection - just open and close the connection each time you need it. Under the covers, ADO.NET will "pool" the connection for you, so that you don't actually have to wait to reconnect.
For any object that implements IDisposable you need to either call .Dispose() on it in a finally block, or wrap it in a using statement. That ensures your resources are properly disposed of. I recommend the using statement, because it helps keep the scope clear.
Your naming conventions should conform to C# standards. Methods that return a boolean should be like IsConnected, not IsConnect. addPlayerBtn_Click should be AddPlayerButton_Click. getLastIdFromDB should be GetlastIdFromDb or getLastIdFromDatabase.
public string GetLastIdFromDatabase()
{
int lastIndex;
string lastID ="";
using (var connection = new MySqlConnection(Configuration.ConnectionString))
using (var command = new MySqlCommand("query", connection))
{
connection.Open();
MySqlDataReader reader = cmd2.ExecuteReader();
while (reader.Read())
{
string item = reader2["ID"].ToString();
lastIndex = int.Parse(item);
lastIndex++;
lastID = lastIndex.ToString();
}
}
return lastID;
}
Note, your query is bad too. I suspect you're using a string data type instead of a number, even though your ID's are number based. You should switch your column to a number data type, then select the max() number. Or use an autoincrementing column or sequence to get the next ID. Reading every single row to determine the next ID and incrementing a counter not good.
I have some tasks (nWorkers = 3):
var taskFactory = new TaskFactory(cancellationTokenSource.Token,
TaskCreationOptions.LongRunning, TaskContinuationOptions.LongRunning,
TaskScheduler.Default);
for (int i = 0; i < nWorkers; i++)
{
var task = taskFactory.StartNew(() => this.WorkerMethod(parserItems,
cancellationTokenSource));
tasks[i] = task;
}
And the following method called by the tasks:
protected override void WorkerMethod(BlockingCollection<ParserItem> parserItems,
CancellationTokenSource cancellationTokenSource)
{
//...log-1...
using (var connection = new OracleConnection(connectionString))
{
OracleTransaction transaction = null;
try
{
cancellationTokenSource.Token.ThrowIfCancellationRequested();
connection.Open();
//...log-2...
transaction = connection.BeginTransaction();
//...log-3...
using (var cmd = connection.CreateCommand())
{
foreach (var parserItem in parserItems.GetConsumingEnumerable(
cancellationTokenSource.Token))
{
cancellationTokenSource.Token.ThrowIfCancellationRequested();
try
{
foreach (var statement in this.ProcessRecord(parserItem))
{
cmd.CommandText = statement;
try
{
cmd.ExecuteNonQuery();
}
catch (OracleException ex)
{
//...log-4...
if (!this.acceptedErrorCodes.Contains(ex.Number))
{
throw;
}
}
}
}
catch (FormatException ex)
{
log.Warn(ex.Message);
}
}
if (!cancellationTokenSource.Token.IsCancellationRequested)
{
transaction.Commit();
}
else
{
throw new Exception("DBComponent has been canceled");
}
}
}
catch (Exception ex)
{
//...log-5...
cancellationTokenSource.Cancel();
if (transaction != null)
{
try
{
transaction.Rollback();
//...log-6...
}
catch (Exception rollbackException)
{
//...log-7...
}
}
throw;
}
finally
{
if (transaction != null)
{
transaction.Dispose();
}
connection.Close();
//...log-8...
}
}
//...log-9...
}
There is a producer of ParserItem objects and these are the consumers. Normally it works fine, there are sometimes that there is an Oracle connection timeout, but in these cases I can see the exception message and everything works as designed.
But sometimes the process get stuck. When it gets stuck, in the log file I can see log-1 message and after that (more or less 15 seconds later) I see log-8 message, but what is driving me nuts is why i cannot see neither the exception message log-5 nor the log-9 message.
Since the cancellationTokenSource.Cancel() method is never called, the producer of items for the bounded collection is stuck until a timeout two hours later.
It is compiled for NET Framework 4 and I'm using Oracle.ManagedDataAccess libraries for the Oracle connection.
Any help would be greatly appreciated.
You should never dispose a transaction or connection when you use using scope. Second, you should rarely rely on exception based programming style. Your code rewritten below:
using (var connection = new OracleConnection(connectionString))
{
using (var transaction = connection.BeginTransaction())
{
connection.Open();
//...log-2...
using (var cmd = connection.CreateCommand())
{
foreach (var parserItem in parserItems.GetConsumingEnumerable(cancellationTokenSource.Token))
{
if (!cancellationTokenSource.IsCancellationRequested)
{
try
{
foreach (var statement in ProcessRecord(parserItem))
{
cmd.CommandText = statement;
try
{
cmd.ExecuteNonQuery();
}
catch (OracleException ex)
{
//...log-4...
if (!acceptedErrorCodes.Contains(ex.ErrorCode))
{
log.Warn(ex.Message);
}
}
}
}
catch (FormatException ex)
{
log.Warn(ex.Message);
}
}
}
if (!cancellationTokenSource.IsCancellationRequested)
{
transaction.Commit();
}
else
{
transaction.Rollback();
throw new Exception("DBComponent has been canceled");
}
}
}
}
//...log-9...
Let me know if this helps.
I can confirm everything you're saying. (program stuck, low CPU usage, oracle connection timeouts, etc.)
One workaround is to use Threads instead of Tasks.
UPDATE: after careful investigation I found out that when you use a high number of Tasks, the ThreadPool worker threads queued by the Oracle driver become slow to start, which ends up causing a (fake) connect timeout.
A couple of solutions for this:
Solution 1: Increase the ThreadPool's minimum number of threads, e.g.:
ThreadPool.SetMinThreads(50, 50); // YMMV
OR
Solution 2: Configure your connection to use pooling and set its minimum size appropriately.
var ocsb = new OracleConnectionStringBuilder();
ocsb.DataSource = ocsb.DataSource;
ocsb.UserID = "myuser";
ocsb.Password = "secret";
ocsb.Pooling = true;
ocsb.MinPoolSize = 20; // YMMV
IMPORTANT: before calling any routine that creates a high number of tasks, open a single connection using that will "warm-up" the pool:
using(var oc = new OracleConnection(ocsb.ToString()))
{
oc.Open();
oc.Close();
}
Note: Oracle indexes the connection pools by the connect string (with the password removed), so if you want to open additional connections you must use always the same exact connect string.
I have a method inside a main one. I need the child method to be able to roll back if the parent method fails. The two data connections use different servers . Before I added the transaction scopes, they worked well. But when I tie them together, the child method aborts.
Edit: Error message: Network access for distributed transaction Manager(MSDTC) has been disabled. Please enable DTC for network access in the security configuration for MSDTC using Component Service Administrative tool.
public static void LoopStudent()
{
try
{
using(TransactionScope scope = new TransactionScope())
{
String connString = ConfigurationManager.AppSettings["DBConnection"];
using(SqlConnection webConn = new SqlConnection(connString))
{
webConn.Open();
String sql = "select * from students";
using(SqlCommand webComm = new SqlCommand(sql, webConn))
{
using(SqlDataReader webReader = webComm.ExecuteReader())
{
if (webReader.HasRows)
{
while (webReader.Read())
{
int i = GetNextId();
}
}
else
Console.WriteLine("wrong");
}
}
}
scope.Complete();
}
}
catch (Exception ex)
{
Console.WriteLine("Error " + ex.Message);
}
} //End LoopThroughCart
public static int GetNextId(String str)
{
int nextId = 0;
String connString = ConfigurationManager.AppSettings["SecondDBConnection"];
try
{
using(TransactionScope scope = new TransactionScope())
{
using(SqlConnection webConn = new SqlConnection(connString))
{
webConn.Open();
using(SqlCommand webComm = new SqlCommand("GetNextId", webConn))
{
//do things
}
}
scope.Complete();
}
}
catch (TransactionAbortedException ex)
{
Console.WriteLine("TransactionAbortedException Message: {0}", ex.Message);
}
catch (ApplicationException ex)
{
Console.WriteLine("ApplicationException Message: {0}", ex.Message);
}
return nextId;
} //End GetNextId
If you do not use RequireNew in you inner method, the inner method will be automatically rolled back if the parent fails to commit the transaction.
What error are you getting?
Alright I originally started out using a Convert.ToInt32(myradTextBox.Text) then it said specified cast is not valid. I did some research on here and decided to try Int.TryParse. Upon doing so I still received this error. What I am trying to do is when the user enters an ID and hits the create button, it searches the DB to see if that ID is already there. I have also tried to convert the bool value from my Int.TryParse to int using Convert.ToInt32(Result) still same error (see below in third code post for where that would be posted). Maybe it has something to do with my comparison method.
Below I have provided the Int.TryParse method with values. The Method I am calling to check the userinput is not in the db currently and my if statement that is catching the statement. Any input on how to fix this would be greatly appreciated. I am still new to most of this stuff so I apologize if leaving any critical info off. Just ask if you need clarification or something elaborated.
Here is my method for comparison:
public bool isValidID(int id)
{
SqlConnection dbConn = null;
int count = 0;
try
{
using (dbConn = new SqlConnection(Properties.Settings.Default["tville"].ToString()))
{
string sql = "SELECT Count(*) FROM PackLabelFormat where PackFormatID = #PackFormatID";
SqlCommand cmd = dbConn.CreateCommand();
cmd.CommandText = sql;
cmd.Parameters.AddWithValue("#PackFormatID", id);
dbConn.Open();
using (SqlDataReader reader = cmd.ExecuteReader())
{
reader.Read();
count = reader.GetInt16(0);
}
}
}
catch (Exception ex)
{
throw ex;
}
if (count > 0)
return false;
return true;
}
Here is my variables that I use in my Int.TryParse method:
string IDselect = rTxtBoxFormatID.Text.ToString();
int resultInt;
bool result = int.TryParse(IDselect, out resultInt);
Lastly here is my method that is catching the error:
SqlConnection dbConn = null;
LabelData labelList = new LabelData();
try
{
using (dbConn = new SqlConnection(Properties.Settings.Default["tville"].ToString()))
{
if (SelectedVersion.isValidID(resultInt))
{
SelectedVersion.PackFormatID = resultInt;
}
else
{
MessageBox.Show("ID already in use!", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
}
catch (Exception ex)
{
throw ex;
}
The database column did not support Int16 aka short. Which was why my specified cast is not valid error never went away no matter what I tried. Thank you for your help in this matter! Here is the code to further illustrate what the problem was.
using (SqlDataReader reader = cmd.ExecuteReader())
{
reader.Read();
//count = reader.GetInt16(0); needs to be reader.GetInt32(0);
}