Model backing a DB Context has changed; Consider Code First Migrations

Question

The model backing the \'MyDbContext\' context has changed since the database was created. Consider using Code First Migrations to update the database (http://

Answer 1

In case you did changes to your context and you want to manually make relevant changes to DB (or leave it as is), there is a fast and dirty way.

Go to DB, and delete everything from "_MigrationHistory" table

Answer 2

Easiest and Safest Method If you know that you really want to change/update your data structure so that the database can sync with your DBContext, The safest way is to:

1. Open up your Package Manager Console
2. Type: update-database -verbose -force

This tells EF to make changes to your database so that it matches your DBContext data structure

Answer 3

This happens when your table structure and model class no longer in sync. You need to update the table structure according to the model class or vice versa -- this is when your data is important and must not be deleted. If your data structure has changed and the data isn't important to you, you can use the DropCreateDatabaseIfModelChanges feature (formerly known as 'RecreateDatabaseIfModelChanges' feature) by adding the following code in your Global.asax.cs:

Database.SetInitializer<MyDbContext>(new DropCreateDatabaseIfModelChanges<MyDbContext>());

Run your application again.

As the name implies, this will drop your database and recreate according to your latest model class (or classes) -- provided you believe the table structure definitions in your model classes are the most current and latest; otherwise change the property definitions of your model classes instead.

Answer 4

You need to believe me. I got this error for the simple reason that I forgot to add the connection string in the App.Config(mine is a wpf project) of your startup project.

The entire config in my case

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
  </configSections>
  <connectionStrings>
    <add name="ZzaDbContext" connectionString="Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=ZaaDbInDepth;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=True;ApplicationIntent=ReadWrite;MultiSubnetFailover=False" providerName="System.Data.SqlClient"/>
  </connectionStrings>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.2" />
  </startup>
  <entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
      <parameters>
        <parameter value="mssqllocaldb" />
      </parameters>
    </defaultConnectionFactory>
    <providers>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
    </providers>
  </entityFramework>
</configuration>

Answer 5

EF codefirst will look at your DbContext, and discover all the entity collections declared in it(and also look at entities related to those entities via navigation properties). It will then look at the database you gave it a connection string to, and make sure all of the tables there match the structure of your entities in model. If they do not match, then it cannot read/write to those tables. Anytime you create a new database, or if you change something about the entity class declarations, such as adding properties or changing data types, then it will detect that the model and the database are not in sync. By default it will simply give you the above error. Usually during development what you want to happen is for the database to be recreated(wiping any data) and generated again from your new model structure.

To do that, see "RecreateDatabaseIfModelChanges Feature" in this article: http://weblogs.asp.net/scottgu/archive/2010/07/16/code-first-development-with-entity-framework-4.aspx

You basically need to provide a database initializer that inherits from DropCreateDatabaseIfModelChanges (RecreateDatabaseIfModelChanges is now deprecated). To do this, simply add this line to the Application_Start method of your Global.asax file.

Database.SetInitializer<NameOfDbContext>(new DropCreateDatabaseIfModelChanges<NameOfDbContext>());

Once you go to production and no longer want to lose data, then you'd remove this initializer and instead use Database Migrations so that you can deploy changes without losing data.

Answer 6

You can fix the issue by deleting the __MigrationHistory table which is created automatically in the database and logs any update in the database using code-first migrations. Here, in this case, you manually changed your database while EF assumed you had to do it with the migration tool. Deleting the table means to the EF that there are no updates and no need to do code-first migrations thus it works perfectly fine.