Entity framework error: context changed since the database was created

Question

I am getting the following error:

An unhandled exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll

Additional information: The model backing the 'PrivateMessageContext' context has changed since the database was created. Consider using Code First Migrations to update the database (http://go.microsoft.com/fwlink/?

But why has it changed? All I want is to get the new message, check if the users have previous message history and either create a new message history or append their current...

I am trying to test the send method, so I want to print out the previous messages each time a new message is added

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.Entity;

namespace CodeFirstNewDatabaseSample
{
class Program
{
    static void Main(string[] args)
    {
            Console.Write("Enter message: ");
            var message = Console.ReadLine();
            var userFrom = "userFrom";
            var userTo = "userTo";
            Methods test = new Methods();
            for(var i=0; i < 10; i++)
            {
                test.StoreMessage(userTo, userFrom, message);
                Console.Write("Enter message: ");
                message = Console.ReadLine();
            }
    }
}
public class PrivateMessageContext : DbContext
{
    public DbSet<PrivateMessageHeader> PrivateMessages { get; set; }
}
public class PrivateMessageHeader
{
    public PrivateMessageHeader() { this.Messages = new List<PrivateMessageDetail>(); }
    public int PrivateMessageHeaderId { get; set; }
    public DateTime TimeStamp { get; set; } // Date of the start of thread
    public string User1 { get; set; }
    public string User2 { get; set; }  // this could be made to a list to allow multiples

    public ICollection<PrivateMessageDetail> Messages { get; set; }
}

public class PrivateMessageDetail
{
    public int PrivateMessageDetailId { get; set; }
    public DateTime MessageDate { get; set; }
    public string FromUser { get; set; } // Don't need ToUser, it's already in header
    public string Message { get; set; }

    public PrivateMessageHeader parent { get; set; }
}
public class Methods
{

    public void StoreMessage(string userTo, string userFrom, string InputMessage) 
    {
        using (var db = new PrivateMessageContext()) 
        {
            var collection = from pm in db.PrivateMessages select pm;
            foreach(var msg in collection)
            {
                var user1 = msg.User1;
                var user2 = msg.User2;
                if ( (user1==userTo && user2==userFrom) || (user1==userFrom && user2==userTo))
                {
                    var msgDetail = new PrivateMessageDetail();
                    msgDetail.FromUser = userFrom;
                    msgDetail.Message = InputMessage;
                    msgDetail.MessageDate = DateTime.Now;
                    msg.Messages.Add(msgDetail);
                    db.SaveChanges(); 
                    return;
                }
            }
            // pair doesn't exist

            var PrivateMessage = new PrivateMessageDetail();
            PrivateMessage.MessageDate = DateTime.Now;
            PrivateMessage.FromUser = userFrom;
            PrivateMessage.Message = InputMessage;
            var newCollection = new PrivateMessageHeader();
            newCollection.TimeStamp = DateTime.Now;
            newCollection.User1 = userTo;
            newCollection.User2 = userFrom;
            newCollection.Messages.Add(PrivateMessage);
            db.PrivateMessages.Add(newCollection); 
            db.SaveChanges();

            var iterator = 0;
            // Display all messages from the database 
            foreach (var pmsg in db.PrivateMessages)
            {

                var query = pmsg;
                var list = pmsg.Messages.ToList();
                foreach (var item in list)
                {
                    Console.WriteLine("msg" + iterator + ":  " + item.ToString());
                }
                iterator++;
            }
            Console.ReadKey();
       }      
   }
}

}

Many thanks

Been sat here warey of sounding stupid, but it's probably inevitable ;) ... doesn't using (var db = new PrivateMessageContext()) at the top of the Send method take care of that? — Fred Johnson

Zafar Zafar · Accepted Answer · 2014-02-10T21:22:17

Have you tried Database.SetInitializer<PrivateMessageContext>(null);?

Try to change your Context as follows.

public class PrivateMessageContext : DbContext
{
    public DbSet<PrivateMessageHeader> PrivateMessages { get; set; }
    protected override void OnModelCreating(DbModelBuilder modelBuilder) {
        Database.SetInitializer<PrivateMessageContext>(null);
    }

}

More info here

Entity framework error: context changed since the database was created

2 Answers