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   go microsoft com fwlink  LinkId 238269     What causes this to happen  I ve literally just created a brand new database and have changed nothing  but every time I try to access a model from a controller it throws this    Edit  It has something to do with the fact that I was attempting to share a connection string  i e  a database  with two separate entities

User · Answer

Just go to Package Manage Console  type the following   Enable-Migrations   If the error like this appears  Unable to update database to match the current model because there are pending changes and automatic migration is disabled  Either write the pending model changes to a code-based migration or enable automatic migration    Do this     Add-Migration   Visual studio will ask for a name  kindly input the name you want   Update-Database

User · Answer

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

User · Answer

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    lt  xml version  1 0  encoding  utf-8   gt   lt configuration gt     lt configSections gt       lt  -- For more information on Entity Framework configuration  visit http   go microsoft com fwlink  LinkID 237468 -- gt       lt section name  entityFramework  type  System Data Entity Internal ConfigFile EntityFrameworkSection  EntityFramework  Version 6 0 0 0  Culture neutral  PublicKeyToken b77a5c561934e089  requirePermission  false    gt     lt  configSections gt     lt connectionStrings gt       lt 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   gt     lt  connectionStrings gt     lt startup gt       lt supportedRuntime version  v4 0  sku   NETFramework Version v4 5 2    gt     lt  startup gt     lt entityFramework gt       lt defaultConnectionFactory type  System Data Entity Infrastructure LocalDbConnectionFactory  EntityFramework  gt         lt parameters gt           lt parameter value  mssqllocaldb    gt         lt  parameters gt       lt  defaultConnectionFactory gt       lt providers gt         lt provider invariantName  System Data SqlClient  type  System Data Entity SqlServer SqlProviderServices  EntityFramework SqlServer    gt       lt  providers gt     lt  entityFramework gt   lt  configuration gt

User · Answer

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    Open up your Package Manager Console Type  update-database -verbose -force   This tells EF to make changes to your database so that it matches your DBContext data structure

User · Answer

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 lt MyDbContext gt  new DropCreateDatabaseIfModelChanges lt MyDbContext gt        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

User · Answer

To solve this error write the the following code in Application Start   Method in Global asax cs file  Database SetInitializer lt MyDbContext gt  null

User · Answer

Entity Framework detects something about the model has changed  you need to do something to the database to get this work  Solution  1  enable-migrations 2  update-database

User · Answer

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

User · Answer

In my case this error was caused by the existence of the  MigrationsHistory table in the database  Deleting that table fixed the problem  Not sure how that table got into our test environment database

User · Answer

Adding this as another possible solution  because this is what fixed it in our case   Make sure if you have multiple projects that they are using the same Entity Framework Nuget package version     In our case we had one project   call if project A   holding the EF code first context with all entities  It was this project that we were using to add migrations  amp  update the database  However a second project   B   was referencing project A to make use of the context  When running this project we got the same error   The model backing the  MyDbContext  context has changed since the database was created  Consider using Code First Migrations to update the database  http   go microsoft com fwlink  LinkId 238269

User · Answer

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 lt NameOfDbContext gt  new DropCreateDatabaseIfModelChanges lt NameOfDbContext gt        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

User · Answer

This error occurs when you have database is not in sync with your model and vice versa  To overcome this   follow the below steps -  a  Add a migration file using  add-migration  lt  Migration File Name    through the        nuget package manager console  This migration file will have the script to sync anything not in sync between Db and code    b  Update the database using  update-database  command  This will update the        database with the latest changes in your model     If this does not help  try these steps after adding the line of code  in the Application Start method of Global asax cs file -  Database SetInitializer lt VidlyDbContext gt  new DropCreateDatabaseIfModelChanges lt VidlyDbContext gt        Reference - http   robertgreiner com 2012 05 unable-to-update-database-to-match-the-current-model-pending-changes

User · Answer

If you have changed the model and database with tables that already exist  and you receive the error  Model backing a DB Context has changed  Consider Code First Migrations  you should    Delete the files under  Migration  folder in your project Open Package Manager console and run pm gt update-database -Verbose

[asp.net-mvc] Model backing a DB Context has changed; Consider Code First Migrations

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