Ado. NET notes--using universal data access

Related knowledge:

1. All of the previous examples, June is access to a specific database (SQL Server), so injected SqlConnection, SqlCommand, SqlDataReader, SqlDataAdapter and other class names added "SQL" prefix, and is subordinate to the System.Data.SqlClient namespace. This poses a huge problem for the portability of the code. If a database is replaced with Oracle, MySQL, or BD2, the code is almost completely rewritten, which is very detrimental to reuse.
2. The System.Data.Common namespace provides a set of classes and operations that allow a program to ignore the differences in the underlying database and make a unified call
   • DbProviderFactories: represents all data providers
   • DbProviderFactory: Represents a specific data provider, for example: System.Data.SqlClient
   • DbConnection, DbCommand, DbDataReader: Object types unrelated to database implementation
3. Using universal database access can make data access code independent of the database to a large extent

Main code:

1 usingSystem;2 usingSystem.Collections.Generic;3 usingSystem.Linq;4 usingSystem.Text;5 usingSystem.Threading.Tasks;6 usingSystem.Data;7 usingSystem.Data.Common;8 9 namespaceConsoleApplication16Ten { One     class Program A     { -         Const stringProvider ="System.Data.SqlClient"; -         Const stringstrconn =@"Server=joe-pc;database=accountdbforsqlinjection;uid=sa;pwd=root"; the  -         Static voidMain (string[] args) -         { -             //get the data provider factory class +DbProviderFactory factory =dbproviderfactories.getfactory (provider); -  +             //creating a Connection object from a factory ADbConnection conn =Factory. CreateConnection (); atConn. ConnectionString =strconn; -  -             //Creating a Command object from a factory -DbCommand cmd =Factory. CreateCommand (); -Cmd. Connection =Conn; -Cmd.commandtext ="SELECT AccountID, AccountName, password from account"; in  -             Try to             { + Conn. Open (); -DbDataReader dr =cmd. ExecuteReader (); the  *                  while(Dr. Read ()) $                 {Panax NotoginsengConsole.WriteLine ("{0}:{1},{2}", dr[0], dr[1], dr[2]); -                 } the             } +             Catch(Exception e) A             { the Console.WriteLine (e); +             } -             finally $             { $ Conn. Close (); -             } -         } the     } -}

ADO. NET notes--using universal data access