C#连接数据库_使用读取配置文件的方式

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;

namespace Students.DAL
{
public class DBHelper
{
public static readonly string conn = ConfigurationManager.ConnectionStrings["ClassRoomConnectionString"].ToString();
public static SqlConnection connection = new SqlConnection(DBHelper.conn);

/// <summary>
/// 增删改数据
/// </summary>
/// <param name="sql"></param>
/// <returns></returns>
public static int ExecuteNonQuery(string sql, SqlParameter[] par)
{
try
{
connection.Open();   //打开数据库连接
SqlCommand comm = new SqlCommand(sql, connection);
//comm.CommandType = System.Data.CommandType.StoredProcedure;
comm.Parameters.AddRange(par);
return comm.ExecuteNonQuery();
}
catch
{
throw;
}
finally
{
connection.Close();
}
}
/// <summary>
/// 增删改数据
/// </summary>
/// <param name="sql"></param>
/// <returns></returns>
public static int ExecuteNonQuery(string sql, SqlParameter[] par, string sql2, SqlParameter[] par2)
{
connection.Open();   //打开数据库连接
SqlTransaction tra = connection.BeginTransaction();
try
{
SqlCommand comm = new SqlCommand(sql, connection);
SqlCommand comm2 = new SqlCommand(sql2, connection);
comm.Parameters.AddRange(par);
comm2.Parameters.AddRange(par2);
comm.Transaction = tra;
comm2.Transaction = tra;
int num1 = comm.ExecuteNonQuery();
int num2 = comm2.ExecuteNonQuery();
int num = comm.ExecuteNonQuery() + comm2.ExecuteNonQuery();
tra.Commit();
return num;
}
catch
{
tra.Rollback();
throw;
}
finally
{
connection.Close();
}
}
/// <summary>
/// 查询数据
/// </summary>
/// <param name="sql"></param>
/// <returns></returns>
public static SqlDataReader ExecuteReader(string sql, SqlParameter[] par)
{
try
{
connection.Open();   //打开数据库连接
SqlCommand comm = new SqlCommand(sql, connection);
//comm.CommandType = System.Data.CommandType.StoredProcedure;
comm.Parameters.AddRange(par);
return comm.ExecuteReader(CommandBehavior.CloseConnection);
}
catch
{
throw;
}
}
/// <summary>
/// 查询数据
/// </summary>
/// <param name="sql"></param>
/// <returns></returns>
public static SqlDataReader ExecuteReader(string sql)
{
try
{
connection.Open();   //打开数据库连接
SqlCommand comm = new SqlCommand(sql, connection);
return comm.ExecuteReader(CommandBehavior.CloseConnection);
}
catch
{
throw;
}
}
/// <summary>
/// 返回单个值
/// </summary>
/// <param name="sql"></param>
/// <returns></returns>
public static object ExecuteScalar(string sql, SqlParameter[] par)
{
try
{
connection.Open();   //打开数据库连接
SqlCommand comm = new SqlCommand(sql, connection);
//comm.CommandType = System.Data.CommandType.StoredProcedure;
comm.Parameters.AddRange(par);
return comm.ExecuteScalar();
}
catch
{
throw;
}
finally
{
connection.Close();
}
}
}
}

然后再App.config文件中写连接语句

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
</startup>
<connectionStrings>
<add name ="ClassRoomConnectionString"
connectionString="Data Source=.;Initial Catalog=StudentDB;User ID=sa;Password=sa"
providerName="System.Data.SqlClient"/>
</connectionStrings>
</configuration>