The model backing the context has chang

Question

The error message :

"The model backing the 'AddressBook' context has changed since the database was created. Either manually delete/update the database, or call Database.SetInitializer with an IDatabaseInitializer instance. For example, the RecreateDatabaseIfModelChanges strategy will automatically delete and recreate the database, and optionally seed it with new data."

I am trying to use the code-first feature and following is what I wrote:

var modelBuilder = new ModelBuilder();
var model = modelBuilder.CreateModel();
using (AddressBook context = new AddressBook(model))
{
    var contact = new Contact
    {
        ContactID = 10000,
        FirstName = "Brian",
        LastName = "Lara",
        ModifiedDate = DateTime.Now,
        AddDate = DateTime.Now,
        Title = "Mr."

    };
    context.contacts.Add(contact);
    int result = context.SaveChanges();
    Console.WriteLine("Result :- "+ result.ToString());
}

The context class:

public class AddressBook : DbContext
{
    public AddressBook()
    { }
    public AddressBook(DbModel AddressBook)
        : base(AddressBook)
    {

    }
    public DbSet<Contact> contacts { get; set; }
    public DbSet<Address> Addresses { get; set; }
}

and the connection string:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <connectionStrings>
    <add name="AddressBook" providerName="System.Data.SqlClient"  
         connectionString="Data Source=MyMachine;Initial Catalog=AddressBook;
         Integrated Security=True;MultipleActiveResultSets=True;"/>
    </connectionStrings>
</configuration>

So, the database name is "AddressBook" and the error happens when I trying to add the contact object to the context. Am I missing anything here?

Answer 1

This fix no longer works after CTP5.

You have to do Database.SetInitializer<YourContext>(null);

Answer 2

I am reading the Pro ASP.NET MVC 4 book as well, and ran into the same problem you were having. For me, I started having the problem after making the changes prescribed in the 'Adding Model Validation' section of the book. The way I resolved the problem is by moving my database from the localdb to the full-blown SQL Server 2012 server. (BTW, I know that I am lucky I could switch to the full-blown version, so don't hate me. ;-))) There must be something with the communication to the db that is causing the problem.

Answer 3

Now it's:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    Database.SetInitializer<YourDbContext>(null);
    base.OnModelCreating(modelBuilder);
}

in your YourDbContext.cs file.

Answer 4

I spent many days to solve this issue, analyzed many different posts and tried many options and finally fixed. This 2 projects in my solution using EF code first migrations:

• Console Application "DataModel" that mainly using as assembly which contains all my code first entities, DbContext, Mirgations and generic repository. I have included to this project separate empty local database file (in DataModel/App_Data folder) to be able generate migrations from Package Manager Console.
• WebApi, which references to DataModel project and uses local database file from WebApi/App_Data folder, that not included in project

I got this error when requested WebApi...

My environment:

• Windows 8.1 x64
• Visual Studio 2015 Professional with Update 1
• all my projects targeted for .NET Framework 4.6.1
• EntityFramework 6.1.3 from NuGet

Here I collected all the remarks you should pay attention and all conditions/requirements which must be met, to avoid mentioned exception :

1. You should use only one version of EntityFramework Nuget package for all projects in your solution.
2. Database, created by running sequentially all migration scripts should have the same structure/schema as you target database and correspond to entity model. Following 3 things must exactly correspond/reflect/match each other:
   • Your all migration script up to last
   • Current code first entity model state (DbContext, entities)
   • Target database
3. Target database (mdf file) should be updated/correspond up to last migration script. Verify that "__MigrationHistory" table in your target database contains records for all migration scripts that you have, it means that all migration scripts was successfully applied to that database. I recommend you to use Visual Studio for generation correct code first entities and context that corresponds to your database, Project -> Add New Item -> ADO.NET Entity Data Model -> Code First from database: Of course, as an alternative, if you have no database you can write manually model (code first entities and context) and then generate initial migration and database.

4. Name of connection string e.g. MyConnectionString in config file of startup project (Web.config/App.config):

   <configuration>
     <connectionStrings>
       <add name="MyConnectionString" connectionString="...">
     </connectionStrings>
   <configuration>
   

   should be equal to parameter passed in constructor of your DbContext:

    public partial class MyDbContext : DbContext
    {
       public MyDbContext()
          : base("name=MyConnectionString"){}
       ...
   

5. Before using Package Manager Console, make sure that you are using correct database for update or generate migration and needed project is set as startup project of solution. For connect to database it will use connection string from that .config file, which in project, that is set as startup project.

6. And the main, which fixed my issue: It is weird, but in my WebApi/bin folder DataModel.exe was old, not refreshed since last build. Since migrations was embedded in my assembly DataModel.exe then my WebApi updated database using old mirgations. I was confused why after updating database in WebApi it not corresponds to latest migration script from DataModel. Following code automatically creates(if not exists) or updates to latest migration local database in my WebApi/App_Data folder.

      public class WebApiApplication : System.Web.HttpApplication
      {
          protected void Application_Start()
          {
              Database.SetInitializer(new MigrateDatabaseToLatestVersion<ODS_DbContext, Configuration>()); 
              ...
   

   I tried clean and rebuild solution but it did not help, than I completely removed bin and obj folders from WebApi, deleted database files from WebApi/App_Data, built, restarted WebApi, made request to it, it created correct database - lazy initialization (using lines above), which corresponds to latest migration and exception didn't appear more. So, this may fix your problem:

   1. remove manually bin, obj folders from your startup project (which generates/updates your database)
   2. build your startup project or better clean and rebuild all you solution.
   3. recreate database by starting project (will execute lines above) or use Package Manager Console "update-database" command.
   4. manually check whether generated db and __MirgationHistory corresponds to latest migration script.

Answer 5

Just in case someone has the same scenario as mine.

I have database first EF and at the same time using the asp.net identity

so I have two connectionStrings in my webconfig, and there is no problem with that. It happened that I created/run the scripts to generate manually the asp.net identity tables which I should not.

so DROP first all the asp.net identity tables created by you manually/from scripts.

DROP TABLE __MigrationHistory
DROP TABLE AspNetRoles
DROP TABLE AspNetUserClaims
DROP TABLE AspNetUserLogins
DROP TABLE AspNetUserRoles
DROP TABLE AspNetUsers

Answer 6

Good suggestion, however, nt so accurate in all cases. I figure one out. Please you need to make sure you run "enable-migrations" using PM windows in Visual Studio, and Migration folder would be added to you project.

Make sure the two c# class files added to the folder on will contain all your models and their respective properties.

If you have all that build the solution, and publis for deployment.

The logic is that the existing metadata cannot be overwritten because your application has no metadata to replace the current. As a result you are getting this error "The model backing the context has changed since the database was created"