首先自定义连接字符串EF5，DB

Question

So I've generated the table I need, and I need the ability to change my connection string when my program is started. At the moment my connection is

"metadata=res://*/entityframework.Model1.csdl|res://*/entityframework.Model1.ssdl
|res://*/entityframework.Model1.msl;provider=MySql.Data.MySqlClient;
provider connection string="server=localhost;User Id=myuserid;
password=12345678;database=databasename""

What I have so far

Get.designer.cs file:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.EntityClient;
using Npgsql;
using System.Configuration;
using System.Data.Entity;
using System.Data.Entity.Validation;
using patientlist.entityframework;
using System.Xml;

namespace patientlist
{
    public partial class Get : Form
    {
        Timer update = new Timer();//60000 = 1min
        public Get()
        {
            InitializeComponent();
        } ....

    private void Timer(object sender, EventArgs e)
    {
        string connectionString = "metadata=res://*/entityframework.Model1.csdl|res://*/entityframework.Model1.ssdl|res://*/entityframework.Model1.msl;provider=MySql.Data.MySqlClient;provider connection string="server=localhost;User Id=myuserid;password=12345678;database=databasename"";

        using (var blah = new ltcsystemEntities())
        {
            blah.Database.Connection.ConnectionString = connectionString;
        } .....

I'm using EF5, and it's DB first (I generated some automated code from my entity model)

Answer 1

With DB First your derived DbContext would have been auto generated for you as a partial class.

public partial class MyContext : DbContext
{
   public MyContext()
   : base("name=MyContext")
   {
   }

//...
}

Notice how it includes a parameterless constructor which calls the parent constructor of method signature: public DbContext(string nameOrConnectionString) ; passing the name of the connection string. This is the connection string that should be in your app.config.

If you need to change connection strings you can write a partial class to complement the autogenerated class and provide a constructor that accepts the name of another app.config connection string or a connection string itself and then pass this to the parent constructor.

public partial class MyContext
{
   public MyContext(String nameOrConnectionString)
   : base(nameOrConnectionString)
   {
   }
}

You could then use as follows.

using(MyContext context = new MyContext(nameOrConnectionString))
{
  //Do stuff
}

However if you are switching connection strings based on some runtime value(s) then you may find it useful to create a factory class to handle the instantiation of your DbContext .

Answer 2

refer Web.config on the root directory of the project.

Your connection strings are located within 'connectionStrings' tag