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This property cannot be set after a connection has been opened

I'm trying to connect to Oracle through .NET Core following this docs:
https://docs.oracle.com/en/database/oracle/oracle-data-access-components/19.3/odpnt/InstallCoreConfiguration.html#GUID-24C963AE-F20B-44B5-800C-594CA06BD24B
But I'm facing this error:
This property cannot be set after a connection has been opened
System.InvalidOperationException: This property cannot be set after a
connection has been opened at
Oracle.ManagedDataAccess.Client.OracleDataSourceCollection.Add(String
tnsName, String tnsDescriptor) at
Infrastructure.Persistence.Factory.ConnectionFactory.SetupOracleConnection()
in
C:\Users\WINDOWS\RiderProjects\TicketsAPI\Infrastructure\Persistence\Factory\ConnectionFactory.cs:line
22
I don't have clue why this is happening, there's my ConnectionFactory:
using System.Data;
using Microsoft.Extensions.Logging;
using Oracle.ManagedDataAccess.Client;
namespace Infrastructure.Persistence.Factory;
public class ConnectionFactory : IConnectionFactory
{
private const string TnsName = "ORCL";
private readonly ILogger<ConnectionFactory> _logger;
public ConnectionFactory(ILogger<ConnectionFactory> logger)
{
_logger = logger;
}
public IDbConnection? Connection => SetupOracleConnection();
private OracleConnection? SetupOracleConnection()
{
OracleConfiguration.OracleDataSources.Add(TnsName,
"(DESCRIPTION =(ADDRESS = (PROTOCOL = TCP)(HOST = DESKTOP-FP8GDE4)(PORT = 1521))(CONNECT_DATA =(SERVER = DEDICATED)(SERVICE_NAME = orcl)))"); // <-- This is the line 22 mentioned in the StackTrace
. . . //Some configs that are in the doc file.
OracleConnection oracleConnection = null!;
try
{
oracleConnection = new OracleConnection($"user id=kevinadmin; password=1234; data source={TnsName}");
oracleConnection.Open();
return oracleConnection;
}
catch (Exception e)
{
_logger.LogError("An error occurred while trying to connect to database {EMessage}", e.Message);
return null;
}
finally
{
oracleConnection?.Close();
}
}
}

[edit:
I may have misunderstood the issue. If the exception is happening on second and subsequent calls to Connection, then this answer might apply]
By declaring your property like
public IDbConnection? Connection => SetupOracleConnection();
you're instructing the { get; } (which is what the => is sugar for) to execute the SetupOracleConnection() every time it is accessed.
You should try to encapsulate that into a singleton instance.
private IDbConnection? _connection = null;
public IDbConnection? Connection => _connection ?? ( _connection = SetupOracleConnection());

Error :Cannot connect to SQL Server Browser. Ensure SQL Server Browser has been started

I share my code to connect to SQLSERVER :
public class Context:DbContext
{
private readonly IDbConn dbConn;
public Context()
{
dbConn = new DbConn();
}
public DbSet<table1> t1{ get; set; }
public DbSet<table2> t2{ get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseSqlServer(dbConn.Connection);
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<table1>().HasKey(x => new { x.column1, x.column2});
modelBuilder.Entity<table2>().HasKey(x => new { x.column1, x.column2});
}
}
public class DbConn : IDbConn
{
private SqlConnection sqlConnection;
public SqlConnection Connection
{
get
{
return new SqlConnection(#"SERVER=xxxxxxx;Initial Catalog=xxxxxxx;User ID=xxxxxx; Password=xxxxxx");
}
}
}
public class Test
{
public static table1 GetFirst()
{
using (var context = new Context())
{
var cb = context.t1.FirstOrDefault(); //The error occurs here
return cb;
}
}
}
I'm a beginner in XAMARIN project.
I try to connect to SQLSERVER and try to get some data from database, but when I execute a LINQ request, I get an error. I already tried to change the connectionStrings but still have the same error.
Can someone help me to resolve this error.
Thanks

I think if your sql server is on a fixed port you can just say what port it is using. Normally not needed for standard ports
return new SqlConnection(#"Data Source=xxxxxxx,portnumberhere;Initial Catalog=xxxxxxx;User ID=xxxxxx; Password=xxxxxx");
if you are using dynamic ports you normally need to give the instance name.
return new SqlConnection(#"Data Source=xxxxxxx\myinstance;Initial Catalog=xxxxxxx;User ID=xxxxxx; Password=xxxxxx");
check no firewalls are blocking traffic between you and the server you are using and as the message says you may in some cases need to ensure the browser service on the database server is running, particularly if using dynamic ports.
Edit:
I think the issue could be where you use
return new SqlConnection(#"SERVER=xxxxxxx;Initial Catalog=xxxxxxx;User ID=xxxxxx; Password=xxxxxx");
instead off
return new SqlConnection(#"Data Source=xxxxxxx;Initial Catalog=xxxxxxx;User ID=xxxxxx; Password=xxxxxx");

Connect to remote DB [duplicate]

New to C# programming, I'd like to be able to access MySQL Databases.
I know MySQL connector/NET and MySQL for Visual Studio are required for C# development.
Do I need to install them into my app?
Is it possible I can just release the connector DLL with the program?
Update:
Are both of them required for the end-user or just the connector?
Is there anything else they would need?

Install Oracle's MySql.Data NuGet package.
using MySql.Data;
using MySql.Data.MySqlClient;
namespace Data
{
public class DBConnection
{
private DBConnection()
{
}
public string Server { get; set; }
public string DatabaseName { get; set; }
public string UserName { get; set; }
public string Password { get; set; }
private MySqlConnection Connection { get; set;}
private static DBConnection _instance = null;
public static DBConnection Instance()
{
if (_instance == null)
_instance = new DBConnection();
return _instance;
}
public bool IsConnect()
{
if (Connection == null)
{
if (String.IsNullOrEmpty(databaseName))
return false;
string connstring = string.Format("Server={0}; database={1}; UID={2}; password={3}", Server, DatabaseName, UserName, Password);
Connection = new MySqlConnection(connstring);
Connection.Open();
}
return true;
}
public void Close()
{
Connection.Close();
}
}
}
Example:
var dbCon = DBConnection.Instance();
dbCon.Server = "YourServer";
dbCon.DatabaseName = "YourDatabase";
dbCon.UserName = "YourUsername";
dbCon.Password = "YourPassword";
if (dbCon.IsConnect())
{
//suppose col0 and col1 are defined as VARCHAR in the DB
string query = "SELECT col0,col1 FROM YourTable";
var cmd = new MySqlCommand(query, dbCon.Connection);
var reader = cmd.ExecuteReader();
while(reader.Read())
{
string someStringFromColumnZero = reader.GetString(0);
string someStringFromColumnOne = reader.GetString(1);
Console.WriteLine(someStringFromColumnZero + "," + someStringFromColumnOne);
}
dbCon.Close();
}

You can use Package Manager to add it as a package and it is the easiest way. You don't need anything else to work with a MySQL database.
Or you can run this command in Package Manager Console:
PM> Install-Package MySql.Data
NuGet MySql.Data

You must to download MySQLConnection NET from here.
Then you need add MySql.Data.DLL to MSVisualStudio like this:
Open menu project
Add
Reference
Browse to C:\Program Files (x86)\MySQL\MySQL Connector Net 8.0.12\Assemblies\v4.5.2
Add MySql.Data.dll
If you want to know more visit: enter link description here
To use in the code you must import the library:
using MySql.Data.MySqlClient;
An example with connectio to Mysql database (NO SSL MODE) by means of Click event:
using System;
using System.Windows;
using MySql.Data.MySqlClient;
namespace Deportes_WPF
{
public partial class Login : Window
{
private MySqlConnection connection;
private string server;
private string database;
private string user;
private string password;
private string port;
private string connectionString;
private string sslM;
public Login()
{
InitializeComponent();
server = "server_name";
database = "database_name";
user = "user_id";
password = "password";
port = "3306";
sslM = "none";
connectionString = String.Format("server={0};port={1};user id={2}; password={3}; database={4}; SslMode={5}", server, port, user, password, database, sslM);
connection = new MySqlConnection(connectionString);
}
private void conexion()
{
try
{
connection.Open();
MessageBox.Show("successful connection");
connection.Close();
}
catch (MySqlException ex)
{
MessageBox.Show(ex.Message + connectionString);
}
}
private void btn1_Click(object sender, RoutedEventArgs e)
{
conexion();
}
}
}

Looking at the code below, I tried it and found:
Instead of writing DBCon = DBConnection.Instance(); you should put DBConnection DBCon - new DBConnection(); (That worked for me)
and instead of MySqlComman cmd = new MySqlComman(query, DBCon.GetConnection()); you should put MySqlCommand cmd = new MySqlCommand(query, DBCon.GetConnection()); (it's missing the d)

Another library to consider is MySqlConnector, https://mysqlconnector.net/. Mysql.Data is under a GPL license, whereas MySqlConnector is MIT.

private void Initialize()
{
server = "localhost";
database = "connectcsharptomysql";
uid = "username";
password = "password";
string connectionString;
connectionString = "SERVER=" + server + ";" + "DATABASE=" +
database + ";" + "U`enter code here`ID=" + uid + ";" + "PASSWORD=" + password + ";";
connection = new MySqlConnection(connectionString);
}

Why is my Entity Framework connection string not working

I am trying to connect to a database without using App.Config but i keep getting the following error:
An unhandled exception of type 'System.Data.Entity.Core.EntityException' occurred in EntityFramework.dll
Additional information: The underlying provider failed on ConnectionString.
I can't see where I've gone wrong so i thought i'd ask here.
namespace MyNameSpace
{
using System;
using System.Data.Entity;
using System.Data.Entity.Core.EntityClient;
using System.Data.Entity.Infrastructure;
public partial class Entities : DbContext
{
public Entities()
: base(entityString.ToString())
{
}
public static EntityConnectionStringBuilder entityString = new EntityConnectionStringBuilder()
{
Provider = "System.Data.SqlServerCe.4.0",
Metadata = "res://*/RS.csdl|res://*/RS.ssdl|res://*/RS.msl",
ProviderConnectionString = #"C:\RestOfPath\database.sdf;Password=3476dfg423434563466e85rcsd"
};
}
}
Thank you in advance for your help.

The problem is that you are passing your sdf file directly on your connection string. Try changing:
ProviderConnectionString = #"C:\RestOfPath\database.sdf;Password=3476dfg423434563466e85rcsd"
To:
ProviderConnectionString = #"Data Source=C:\RestOfPath\database.sdf;Password=3476dfg423434563466e85rcsd"
Or better yet, use a SqlCeConnectionStringBuilder to construct this property:
var connectionStringBuilder = new SqlCeConnectionStringBuilder();
connectionStringBuilder.DataSource = #"C:\RestOfPath\database.sdf";
connectionStringBuilder.Password = "3476dfg423434563466e85rcsd";
EFConnectionBuilder.ProviderConnectionString = connectionStringBuilder.ToString(),

Try this : make this parameterise
public Entities(string connString)
: base(connString)
{
}
and pass string connection string when creating object of Context class.
public class TestController : Controller
{
Entity _context = new Entity("data source=Dev-4;initial catalog=test1;
integrated security=True;MultipleActiveResultSets=True;
App=EntityFramework");
}

Try this : here you din't need to pass connection string again and again -->
public Model1()
: base(connString)
{
}
public static string connString = "data source=tesst;initial catalog=test1;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework";
Use This method when using Database First Model of Entity Framework :
public test1Entities()
: base(nameOrConnectionString: ConnectionString())
{
}
private static string ConnectionString()
{
SqlConnectionStringBuilder sqlBuilder = new SqlConnectionStringBuilder();
sqlBuilder.DataSource = "DEV-4";
sqlBuilder.InitialCatalog = "test1";
sqlBuilder.PersistSecurityInfo = true;
sqlBuilder.IntegratedSecurity = true;
sqlBuilder.MultipleActiveResultSets = true;
EntityConnectionStringBuilder entityBuilder = new EntityConnectionStringBuilder();
entityBuilder.ProviderConnectionString = sqlBuilder.ToString();
entityBuilder.Metadata = "res://*/";
entityBuilder.Provider = "System.Data.SqlClient";
return entityBuilder.ToString();
}

Failover connection string in n-tier linq2sql

Scenario: ASP.Net web app (n-tier linq2sql) on local IIS with connection to SQL 2008 database over VPN. Some data is replicated to a local SQL 2008 express DB (different name). If the connection is down to VPN database, we would like to use the local instance for some parts of the web app.
My Question is, how can the following solution be improved. we have involves a lot of passing the connection string about. If this involved mirroring, we could set the failover partner but as it is a different database I don't think this is possible.
Current Code:
Check if we can connect remotely, put the working connection string in session
Session_Start()
{
//if can connect to remote db
Session["ConnStr"] = //remote connection
//else
Session["ConnStr"] = //local connection
}
Pass connection string in UI to BLL
protected void ods1_ObjectCreating(object sender, ObjectDataSourceEventArgs e)
{
TestManager myTestManager = new TestManager(Session["ConnString"].ToString());
e.ObjectInstance = myTestManager;
}
Pass to DAL
public class TestManager
{
private readonly string _connectionString;
public TestManager(string connectionString)
{
_connectionString = connectionString;
}
[DataObjectMethod(DataObjectMethodType.Select, true)]
public List<Test> GetAll()
{
TestDB testDB = new TestDB(_connectionString);
return testDB.GetAll();
}
}
Set connection in DAL creating DataContext in constructor
public class TestDB
{
public TestDB(string connectionString)
{
_connectionString = connectionString;
_dbContext = new TestDataContext(_connectionString);
}
private TestDataContext _dbContext;
private string _connectionString;
public string ConnectionString
{
get
{
return _connectionString;
}
set
{
_connectionString = value;
}
}
public TestDataContext DbContext
{
get
{
return _dbContext;
}
set
{
_dbContext = value;
}
}
public List<Test> GetAll()
{
var query = from t in DbContext.Tests
select new DTO.Test()
{
Id = t.Id,
Name = t.Name
};
return query.ToList();
}