Develop Reference

Oracle Managed DataAccess connection object is keeping the connection open

I'm using Oracle.ManagedDataAccess Nuget package version 18.3.0. I tried many things. I tried to dispose everything I can think of, even oracle parameters objects. And wrapped everything inside a using block but to no avail. The only thing that actually worked for me is that the commented line OracleConnection.ClearPool(oracle);. Is this a bug, or some configuration related issue, or am I misunderstand things here? Also, I tried to remove the reference of Oracle.ManagedDataAccess and replaced it with a reference to System.Data.OracleClient and that actually worked for me. It automatically closed the connection, so no connection left with "In-Active" status. The code below I moved it into a simple, single button, Windows Forms application to make 100% sure nothing is interfering and the problem still occurring.
using (var oracle = new OracleConnection("Data Source=(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=myhost)(PORT=SomePortHere))(CONNECT_DATA=(SERVER=SHARED)(SERVICE_NAME=anotherHost)))", new OracleCredential(userName,password)))
{
oracle.Open();
using (var command = new OracleCommand())
{
var query = "SELECT x from y where z=:param1";
command.Connection = oracle;
command.CommandText = query;
command.CommandType = System.Data.CommandType.Text;
var param1 = new OracleParameter(":param1", xyz);
command.Parameters.Add(param1);
using (var reader = command.ExecuteReader())
{
if (reader.Read())
{
//read the data from the reader
}
}
param1.Dispose();
}
//If this line is commented, there will be a connection left open, with InActive status
//OracleConnection.ClearPool(oracle);
}
password.Dispose();
return myData;
And this is an image to show the opened connection through Toad.
Of course, for each click to that button, the code above will execute and a new session will remain open, until what you see in the image.
The name "TheTesterOfAllTests.exe" is the Windows Forms app.
Is this a configuration problem?
Is there any way to solve this issue other than using ClearPool method? Because it affects the performance of the app.
P.S. The application that is originally using the code above is a WCF Service that is consumed by a Web application.
P.S. 2 There is some kind of memory leakage, with each click to that button the memory usage increases

I ran into the same problem.
I solved it by changing the initialization of the OracleConnection.
from
var con = new OracleConnection(
"Data Source=(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=myhost)(PORT=SomePortHere))(CONNECT_DATA=(SERVER=SHARED)(SERVICE_NAME=anotherHost)))",
new OracleCredential(userName,password));
to
var con = new OracleConnection(
"USER ID=myuser;PASSWORD=mypwd;Data Source=(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=myhost)(PORT=SomePortHere))(CONNECT_DATA=(SERVER=SHARED)(SERVICE_NAME=anotherHost)))");
To me, this different behavior looks like a bug.
As a result, i can no longer use OracleCredential and must store the password as a string. That's okay for me.
remark: SecureString shouldn't be used

It turns out the problem is in the way internally oracle creates connection, since for each newly created OracleConnection object, a new Connection is added to the Connection pool. I counted 91 connection entry in the connection pool.
The solution was to use one OracleConnection instance for each request "Per Request Scope". I implemented that by using a simple generic IDatabase<TConnection> interface with one TConnection GetConnection<TConnection>() method and of course for each method that will be called on that same request's instance, a pair of Open/Close call will take place so we don't keep the connection open the whole time.
Regarding the memory leak, I'm still not able to 100% confirm this, but when I used the Oracle.DataAccess.Client library instead of Oracle.ManagedDataAccess the memory usage reduced dramatically. So, I switched back to Oracle.DataAccess.Client.
P.S. I will update this answer in case of new information regarding these two issues, and contributions are very welcome, maybe I misunderstand something regarding how Oracle deals with the database connection.

Data missing from Access database after added using textboxes [duplicate]

I have following C# code in a console application.
Whenever I debug the application and run the query1 (which inserts a new value into the database) and then run query2 (which displays all the entries in the database), I can see the new entry I inserted clearly. However, when I close the application and check the table in the database (in Visual Studio), it is gone. I have no idea why it is not saving.
using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlServerCe;
using System.Data;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
try
{
string fileName = "FlowerShop.sdf";
string fileLocation = "|DataDirectory|\\";
DatabaseAccess dbAccess = new DatabaseAccess();
dbAccess.Connect(fileName, fileLocation);
Console.WriteLine("Connected to the following database:\n"+fileLocation + fileName+"\n");
string query = "Insert into Products(Name, UnitPrice, UnitsInStock) values('NewItem', 500, 90)";
string res = dbAccess.ExecuteQuery(query);
Console.WriteLine(res);
string query2 = "Select * from Products";
string res2 = dbAccess.QueryData(query2);
Console.WriteLine(res2);
Console.ReadLine();
}
catch (Exception e)
{
Console.WriteLine(e);
Console.ReadLine();
}
}
}
class DatabaseAccess
{
private SqlCeConnection _connection;
public void Connect(string fileName, string fileLocation)
{
Connect(#"Data Source=" + fileLocation + fileName);
}
public void Connect(string connectionString)
{
_connection = new SqlCeConnection(connectionString);
}
public string QueryData(string query)
{
_connection.Open();
using (SqlCeDataAdapter da = new SqlCeDataAdapter(query, _connection))
using (DataSet ds = new DataSet("Data Set"))
{
da.Fill(ds);
_connection.Close();
return ds.Tables[0].ToReadableString(); // a extension method I created
}
}
public string ExecuteQuery(string query)
{
_connection.Open();
using (SqlCeCommand c = new SqlCeCommand(query, _connection))
{
int r = c.ExecuteNonQuery();
_connection.Close();
return r.ToString();
}
}
}
EDIT: Forgot to mention that I am using SQL Server Compact Edition 4 and VS2012 Express.

It is a quite common problem. You use the |DataDirectory| substitution string. This means that, while debugging your app in the Visual Studio environment, the database used by your application is located in the subfolder BIN\DEBUG folder (or x86 variant) of your project. And this works well as you don't have any kind of error connecting to the database and making update operations.
But then, you exit the debug session and you look at your database through the Visual Studio Server Explorer (or any other suitable tool). This window has a different connection string (probably pointing to the copy of your database in the project folder). You search your tables and you don't see the changes.
Then the problem get worse. You restart VS to go hunting for the bug in your app, but you have your database file listed between your project files and the property Copy to Output directory is set to Copy Always. At this point Visual Studio obliges and copies the original database file from the project folder to the output folder (BIN\DEBUG) and thus your previous changes are lost.
Now, your application inserts/updates again the target table, you again can't find any error in your code and restart the loop again until you decide to post or search on StackOverflow.
You could stop this problem by clicking on the database file listed in your Solution Explorer and changing the property Copy To Output Directory to Copy If Newer or Never Copy. Also you could update your connectionstring in the Server Explorer to look at the working copy of your database or create a second connection. The first one still points to the database in the project folder while the second one points to the database in the BIN\DEBUG folder. In this way you could keep the original database ready for deployment purposes and schema changes, while, with the second connection you could look at the effective results of your coding efforts.
EDIT Special warning for MS-Access database users. The simple act of looking at your table changes the modified date of your database ALSO if you don't write or change anything. So the flag Copy if Newer kicks in and the database file is copied to the output directory. With Access better use Copy Never.

Committing changes / saving changes across debug sessions is a familiar topic in SQL CE forums. It is something that trips up quite a few people. I'll post links to source articles below, but I wanted to paste the answer that seems to get the best results to the most people:
You have several options to change this behavior. If your sdf file is part of the content of your project, this will affect how data is persisted. Remember that when you debug, all output of your project (including the sdf) if in the bin/debug folder.
You can decide not to include the sdf file as part of your project and manage the file location runtime.
If you are using "copy if newer", and project changes you make to the database will overwrite any runtime/debug changes.
If you are using "Do not copy", you will have to specify the location in code (as two levels above where your program is running).
If you have "Copy always", any changes made during runtime will always be overwritten
Answer Source
Here is a link to some further discussion and how to documentation.

Saving data in a Database C# WPF [duplicate]

I have following C# code in a console application.
Whenever I debug the application and run the query1 (which inserts a new value into the database) and then run query2 (which displays all the entries in the database), I can see the new entry I inserted clearly. However, when I close the application and check the table in the database (in Visual Studio), it is gone. I have no idea why it is not saving.
using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlServerCe;
using System.Data;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
try
{
string fileName = "FlowerShop.sdf";
string fileLocation = "|DataDirectory|\\";
DatabaseAccess dbAccess = new DatabaseAccess();
dbAccess.Connect(fileName, fileLocation);
Console.WriteLine("Connected to the following database:\n"+fileLocation + fileName+"\n");
string query = "Insert into Products(Name, UnitPrice, UnitsInStock) values('NewItem', 500, 90)";
string res = dbAccess.ExecuteQuery(query);
Console.WriteLine(res);
string query2 = "Select * from Products";
string res2 = dbAccess.QueryData(query2);
Console.WriteLine(res2);
Console.ReadLine();
}
catch (Exception e)
{
Console.WriteLine(e);
Console.ReadLine();
}
}
}
class DatabaseAccess
{
private SqlCeConnection _connection;
public void Connect(string fileName, string fileLocation)
{
Connect(#"Data Source=" + fileLocation + fileName);
}
public void Connect(string connectionString)
{
_connection = new SqlCeConnection(connectionString);
}
public string QueryData(string query)
{
_connection.Open();
using (SqlCeDataAdapter da = new SqlCeDataAdapter(query, _connection))
using (DataSet ds = new DataSet("Data Set"))
{
da.Fill(ds);
_connection.Close();
return ds.Tables[0].ToReadableString(); // a extension method I created
}
}
public string ExecuteQuery(string query)
{
_connection.Open();
using (SqlCeCommand c = new SqlCeCommand(query, _connection))
{
int r = c.ExecuteNonQuery();
_connection.Close();
return r.ToString();
}
}
}
EDIT: Forgot to mention that I am using SQL Server Compact Edition 4 and VS2012 Express.

It is a quite common problem. You use the |DataDirectory| substitution string. This means that, while debugging your app in the Visual Studio environment, the database used by your application is located in the subfolder BIN\DEBUG folder (or x86 variant) of your project. And this works well as you don't have any kind of error connecting to the database and making update operations.
But then, you exit the debug session and you look at your database through the Visual Studio Server Explorer (or any other suitable tool). This window has a different connection string (probably pointing to the copy of your database in the project folder). You search your tables and you don't see the changes.
Then the problem get worse. You restart VS to go hunting for the bug in your app, but you have your database file listed between your project files and the property Copy to Output directory is set to Copy Always. At this point Visual Studio obliges and copies the original database file from the project folder to the output folder (BIN\DEBUG) and thus your previous changes are lost.
Now, your application inserts/updates again the target table, you again can't find any error in your code and restart the loop again until you decide to post or search on StackOverflow.
You could stop this problem by clicking on the database file listed in your Solution Explorer and changing the property Copy To Output Directory to Copy If Newer or Never Copy. Also you could update your connectionstring in the Server Explorer to look at the working copy of your database or create a second connection. The first one still points to the database in the project folder while the second one points to the database in the BIN\DEBUG folder. In this way you could keep the original database ready for deployment purposes and schema changes, while, with the second connection you could look at the effective results of your coding efforts.
EDIT Special warning for MS-Access database users. The simple act of looking at your table changes the modified date of your database ALSO if you don't write or change anything. So the flag Copy if Newer kicks in and the database file is copied to the output directory. With Access better use Copy Never.

Committing changes / saving changes across debug sessions is a familiar topic in SQL CE forums. It is something that trips up quite a few people. I'll post links to source articles below, but I wanted to paste the answer that seems to get the best results to the most people:
You have several options to change this behavior. If your sdf file is part of the content of your project, this will affect how data is persisted. Remember that when you debug, all output of your project (including the sdf) if in the bin/debug folder.
You can decide not to include the sdf file as part of your project and manage the file location runtime.
If you are using "copy if newer", and project changes you make to the database will overwrite any runtime/debug changes.
If you are using "Do not copy", you will have to specify the location in code (as two levels above where your program is running).
If you have "Copy always", any changes made during runtime will always be overwritten
Answer Source
Here is a link to some further discussion and how to documentation.

Beginner requests Help with Mysql and C#

I'm trying to build a program that uses a C# to work with a MySQL DB. I get the C# syntax, and can write the language, but I don't have much experience with the libraries, and I feel a bit lost.
Could someone post examples of how a program would be built (in technical terms, syntax would be nice, but pseudo code is fine, too)?
I understand the theory of how it works, but need a hands on approach to it.
Thank you.
EDIT
I forgot to add that I want to learn how to do it with the .NET v.2.0 framework / VS2005 / MySQL v5.0 combination.
EDIT # 2
2.0 .NET will only be supported. =)

Here is tutorial for Entity Framework + MySQL.
There are lots of other ways to operate with DB, depending on what you need:
If you need execute raw sql queries against DB - use OdbcConnection + OdbcCommand
Need to manipulate items in DB as objects - use ORM (EntityFramework, NHibernate, Linq2Sql)
Like old-style DB interop? - DataSets is your choice.
I really like EF. Easy thing to start with.
PS: And before mixing UI and DB-interop, please read about Separation of concerns. MVC is interesting to read about too. About "libraries": create another project in your solution and add DB-interop logics there. Don't mix it in one assembly, because when your project becomes bigger than "Hello DataBase!" application it will create a big mess in code and logics, really.
UPDATE:
Using VS2005 and .net 2.0 is mysterious idea, really. Lots of tools and assemblies where made since 2.0 release. Linq, Orm-s, etc. Live without them is hard and all the benefits of C# are lost. I highly recommend to use latest techniques, if there is no strict reasons to use 2.0.
If using SqlServer - ObdcCommand and OdbcConnection can be replaced to SqlCommand and SqlConnection. (thanks #Abe Miessler comment)

Here is an example swiped from MSDN:
public void InsertRow(string connectionString, string insertSQL)
{
using (OdbcConnection connection =
new OdbcConnection(connectionString))
{
// The insertSQL string contains a SQL statement that
// inserts a new row in the source table.
OdbcCommand command = new OdbcCommand(insertSQL, connection);
// Open the connection and execute the insert command.
try
{
connection.Open();
command.ExecuteNonQuery();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
// The connection is automatically closed when the
// code exits the using block.
}
}
If you want to read records in a DB, look at this example:
public static void ReadData(string connectionString)
{
string queryString = "SELECT DISTINCT CustomerID FROM Orders";
using (OdbcConnection connection = new OdbcConnection(connectionString))
{
OdbcCommand command = new OdbcCommand(queryString, connection);
connection.Open();
// Execute the DataReader and access the data.
OdbcDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Console.WriteLine("CustomerID={0}", reader[0]);
}
// Call Close when done reading.
reader.Close();
}
}
FYI i am just copy/pasting these directly from MSDN. I highly recommend reading over their documentation and looking at their examples if you are just getting started.
http://msdn.microsoft.com/en-us/library/system.data.odbc.odbcdatareader.aspx

Here is a blog post getting you started with MySql and C#.
http://blog.bobcravens.com/2010/06/the-repository-pattern-with-linq-to-fluent-nhibernate-and-mysql/
Hope that gets you started.
Bob

What is the best way to connect and use a sqlite database from C#

I've done this before in C++ by including sqlite.h but is there a similarly easy way in C#?

I'm with, Bruce. I AM using http://system.data.sqlite.org/ with great success as well. Here's a simple class example that I created:
using System;
using System.Text;
using System.Data;
using System.Data.SQLite;
namespace MySqlLite
{
class DataClass
{
private SQLiteConnection sqlite;
public DataClass()
{
//This part killed me in the beginning. I was specifying "DataSource"
//instead of "Data Source"
sqlite = new SQLiteConnection("Data Source=/path/to/file.db");
}
public DataTable selectQuery(string query)
{
SQLiteDataAdapter ad;
DataTable dt = new DataTable();
try
{
SQLiteCommand cmd;
sqlite.Open(); //Initiate connection to the db
cmd = sqlite.CreateCommand();
cmd.CommandText = query; //set the passed query
ad = new SQLiteDataAdapter(cmd);
ad.Fill(dt); //fill the datasource
}
catch(SQLiteException ex)
{
//Add your exception code here.
}
sqlite.Close();
return dt;
}
}
There is also an NuGet package: System.Data.SQLite available.

Microsoft.Data.Sqlite by Microsoft has over 9000 downloads every day, so I think you are safe using that one.
Example usage from the documentation:
using (var connection = new SqliteConnection("Data Source=hello.db"))
{
connection.Open();
var command = connection.CreateCommand();
command.CommandText =
#"
SELECT name
FROM user
WHERE id = $id
";
command.Parameters.AddWithValue("$id", id);
using (var reader = command.ExecuteReader())
{
while (reader.Read())
{
var name = reader.GetString(0);
Console.WriteLine($"Hello, {name}!");
}
}
}

I've used this with great success:
http://system.data.sqlite.org/
Free with no restrictions.
(Note from review: Original site no longer exists. The above link has a link pointing the the 404 site and has all the info of the original)
--Bruce

There is a list of Sqlite wrappers for .Net at http://www.sqlite.org/cvstrac/wiki?p=SqliteWrappers. From what I've heard http://sqlite.phxsoftware.com/ is quite good. This particular one lets you access Sqlite through ADO.Net just like any other database.

There's also now this option: http://code.google.com/p/csharp-sqlite/ - a complete port of SQLite to C#.

https://github.com/praeclarum/sqlite-net is now probably the best option.

Another way of using SQLite database in NET Framework is to use Fluent-NHibernate.
[It is NET module which wraps around NHibernate (ORM module - Object Relational Mapping) and allows to configure NHibernate programmatically (without XML files) with the fluent pattern.]
Here is the brief 'Getting started' description how to do this in C# step by step:
https://github.com/jagregory/fluent-nhibernate/wiki/Getting-started
It includes a source code as an Visual Studio project.

Here I am trying to help you do the job step by step: (this may be the answer to other questions)
Go to this address , down the page you can see something like "List of Release Packages". Based on your system and .net framework version choose the right one for you. for example if your want to use .NET Framework 4.6 on a 64-bit Windows, choose this version and download it.
Then install the file somewhere on your hard drive, just like any other software.
Open Visual studio and your project. Then in solution explorer, right-click on "References" and choose "add Reference...".
Click the browse button and choose where you install the previous file and go to .../bin/System.Data.SQLite.dll and click add and then OK buttons.
that is pretty much it. now you can use SQLite in your project.
to use it in your project on the code level you may use this below example code:
make a connection string:
string connectionString = #"URI=file:{the location of your sqlite database}";
establish a sqlite connection:
SQLiteConnection theConnection = new SQLiteConnection(connectionString );
open the connection:
theConnection.Open();
create a sqlite command:
SQLiteCommand cmd = new SQLiteCommand(theConnection);
Make a command text, or better said your SQLite statement:
cmd.CommandText = "INSERT INTO table_name(col1, col2) VALUES(val1, val2)";
Execute the command
cmd.ExecuteNonQuery();
that is it.

Mono comes with a wrapper, use theirs!
https://github.com/mono/mono/tree/master/mcs/class/Mono.Data.Sqlite/Mono.Data.Sqlite_2.0 gives code to wrap the actual SQLite dll ( http://www.sqlite.org/sqlite-shell-win32-x86-3071300.zip found on the download page http://www.sqlite.org/download.html/ ) in a .net friendly way. It works on Linux or Windows.
This seems the thinnest of all worlds, minimizing your dependence on third party libraries. If I had to do this project from scratch, this is the way I would do it.

if you have any problem with the library you can use Microsoft.Data.Sqlite;
public static DataTable GetData(string connectionString, string query)
{
DataTable dt = new DataTable();
Microsoft.Data.Sqlite.SqliteConnection connection;
Microsoft.Data.Sqlite.SqliteCommand command;
connection = new Microsoft.Data.Sqlite.SqliteConnection("Data Source= YOU_PATH_BD.sqlite");
try
{
connection.Open();
command = new Microsoft.Data.Sqlite.SqliteCommand(query, connection);
dt.Load(command.ExecuteReader());
connection.Close();
}
catch
{
}
return dt;
}
you can add NuGet Package Microsoft.Data.Sqlite