C # Connection database--commonly used at present

Use C # to implement the user name login---Connect to the database, query and determine if there is a user name

First, the link class

1. Add DbConnection Class

2 Construction

    public class DBConnection    {        private static string _connectionstring = null;        public static SqlConnection Connection        {            get            {                //reads the link string from the configuration file                _connectionstring = configurationmanager.connectionstrings["MyDB"]. ConnectionString;                Building a Connection object using a link string                SqlConnection conn = new SqlConnection (_connectionstring);                Return conn;}}    }

(You can also define a string variable in get{} to receive the configuration)

    public class DBConnection    {public                static SqlConnection Connection        {            get            }                //Read link string from configuration file                string  _connectionstring = configurationmanager.connectionstrings["MyDB"]. ConnectionString;                Building a Connection object using a link string                SqlConnection conn = new SqlConnection (_connectionstring);                Return conn;}}    }

Second, add the configuration file

1. Reference right-click to add System.Configuration reference

2. Add New Item--Application configuration file

3.app.config

  <connectionStrings>    <add name= "mydb" connectionstring= "server=.; Database=mydb;uid=sa;pwd=123 "/>  </connectionStrings>

Note: The name name in the configuration file is the same as the field in Connectionstring["" in the DbConnection class

Third, open the close database

The 1.Main function calls the Connection property inside the DbConnection class

Class program    {        static void Main (string[] args)        {            SqlConnection conn = dbconnection.connection;            Console.WriteLine (Conn. State);            Conn. Open ();            Console.WriteLine (Conn. State);            Conn. Close ();            Console.WriteLine (Conn. State);        }    }

Execution results

C # Connection database--commonly used at present