不支持的关键字：“数据源”

我是新来的Entity framework。我只是尝试代码优先模式。我想将数据插入到学生表中。

//this is the insert.cs code

public class Insertingvalue
{
     public Insertingvalue()
     {

     }

     public static void addvalue()
     {
         var newstudent=new Student();
         newstudent.student_id= 008;
         newstudent.student_name = "lakshmi";
         newstudent.class_name = "12th";
         newstudent.mark1 = 60;
         newstudent.mark2 = 70;
         newstudent.mark3 = 80;

         using (var dbcon=new Context())
         {
             //dbcon.Database.Connection.Open();
             dbcon.Students.Add(newstudent);
             dbcon.SaveChanges();
         }
     }
}

我的连接字符串如下

    <connectionStrings>
        <add name="Context" 
             connectionString="Data Source=AFRESH-PC\SQLEXPRESS;
             Initial Catalog=laks;
             Integrated Security=True;
             App=EntityFramework" 
             providerName="System.Data.EntityClient"/>
    </connectionStrings>

错误是不支持关键字：“数据源”。我无法修复此bug.pls帮助我