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.NET C# Java Javascript Exception

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Recently I needed to write a module that needs to connect to a wide range of SQL-DBs, e.g. MySQL, MS SQL, Oracle etc.

Problem: Most providers will use their concret classes

If you look at the C# example on the MySQL dev page you will see the MsSql-Namespace and classes:

MySql.Data.MySqlClient.MySqlConnection conn;
string myConnectionString;

myConnectionString = "server=127.0.0.1;uid=root;" +
 "pwd=12345;database=test;";

try
{
 conn = new MySql.Data.MySqlClient.MySqlConnection();
 conn.ConnectionString = myConnectionString;
 conn.Open();
}
catch (MySql.Data.MySqlClient.MySqlException ex)
{
 MessageBox.Show(ex.Message);
}

The same classes will probably not work for a MS SQL database.

“Solution”: Use the DbProviderFactories

For example if you install the MySql-NuGet package you will also get this little enhancement to you app.config:

<system.data>
 <DbProviderFactories>
 <remove invariant="MySql.Data.MySqlClient" />
 <add name="MySQL Data Provider" invariant="MySql.Data.MySqlClient" description=".Net Framework Data Provider for MySQL" type="MySql.Data.MySqlClient.MySqlClientFactory, MySql.Data, Version=6.9.9.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d" />
 </DbProviderFactories>
</system.data>

Now we can get a reference to the MySql client via the DbProviderFactories:

using System;
using System.Data;
using System.Data.Common;

namespace DbProviderFactoryStuff
{
 class Program
 {
 static void Main(string[] args)
 {
 try
 {
 Console.WriteLine("All registered DbProviderFactories:");
 var allFactoryClasses = DbProviderFactories.GetFactoryClasses();

 foreach (DataRow row in allFactoryClasses.Rows)
 {
 Console.WriteLine(row[0] + ": " + row[2]);
 }

 Console.WriteLine();
 Console.WriteLine("Try to access a MySql DB:");

 DbProviderFactory dbf = DbProviderFactories.GetFactory("MySql.Data.MySqlClient");
 using (DbConnection dbcn = dbf.CreateConnection())
 {
 dbcn.ConnectionString = "Server=localhost;Database=testdb;Uid=root;Pwd=Pass1word;";
 dbcn.Open();
 using (DbCommand dbcmd = dbcn.CreateCommand())
 {
 dbcmd.CommandType = CommandType.Text;
 dbcmd.CommandText = "SHOW TABLES;";

 // parameter...
 //var foo = dbcmd.CreateParameter();
 //foo.ParameterName = "...";
 //foo.Value = "...";

 using (DbDataReader dbrdr = dbcmd.ExecuteReader())
 {
 while (dbrdr.Read())
 {
 Console.WriteLine(dbrdr[0]);
 }
 }
 }
 }
 }
 catch (Exception exc)
 {
 Console.WriteLine(exc.Message);
 }

 Console.ReadLine();

 }
 }
}

The most important line is this one:

DbProviderFactory dbf = DbProviderFactories.GetFactory("MySql.Data.MySqlClient");

Now with the DbProviderFactory from the MySql client we can access the MySql database without using any MySql-specific classes.

There are a couple of “in-built” db providers registered, like the MS SQL provider or ODBC stuff.

The above code will output something like this:

All registered DbProviderFactories:
Odbc Data Provider: System.Data.Odbc
OleDb Data Provider: System.Data.OleDb
OracleClient Data Provider: System.Data.OracleClient
SqlClient Data Provider: System.Data.SqlClient
Microsoft SQL Server Compact Data Provider 4.0: System.Data.SqlServerCe.4.0
MySQL Data Provider: MySql.Data.MySqlClient

Other solutions

Of course there are other solutions - some OR-Mapper like the EntityFramework have a provider model which might also work, but this one here is a pretty basic approach.

SQL Commands

The tricky bit here is that you need to make sure that your SQL commands work on your database - this is not a silver bullet, it just lets you connect and execute SQL commands to any ‘registered’ database.

The full demo code is also available on GitHub.

Hope this helps.

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