I know a lot of answer for this question is available here but I have tried all out and not working. Maybe because my issue is different..
So i have an application already already in use with code-first approach. More than a year now. But there is the need to add some functionality which requires new fields to existing tables and also additional tables.
I am done adding this on local system. I want to do migration for it but bringing error
There is already an object named 'BookInvestments' in the database BookInvestment is an already existing table in the database by the way..
I have deleted the migration table on the Database and issue persist.
Please note that the namespace of the application remains same
I have also deleted the files created in the migration folder on my visual studio in trying to create new migrations and update database but issue persist.
I have records in the database and I cannot discard it as client has to make use of it going forward as well.
Please what do you suggest I do?
Related
I'm working on an application with asp.net mvc that supports install, remove plugins.
When I want to install a new plugin I have an Install method that registers new routes and ...
For database, I use a code-first approach for creating database and every plugin has it's own context class.
My question is: when I want to install a new plugin, I need to create additional tables in my existing database, or create a new database if the database does not yet exist. And if those tables are already there, nothing should be created.
How do I achieve this?
Thanks in advance
Code First Migrations has two primary commands that you are going to become familiar with
Add-Migration will scaffold the next migration based on changes you
have made to your model since the last migration was created
Update-Database will apply any pending migrations to the database
When you develop a new application, your data model changes frequently, and each time the model changes, it gets out of sync with the database. You have configured the Entity Framework to automatically drop and re-create the database each time you change the data model. When you add, remove, or change entity classes or change your DbContext class, the next time you run the application it automatically deletes your existing database, creates a new one that matches the model, and seeds it with test data.
This method of keeping the database in sync with the data model works well until you deploy the application to production. When the application is running in production it is usually storing data that you want to keep, and you don't want to lose everything each time you make a change such as adding a new column. The Code First Migrations feature solves this problem by enabling Code First to update the database schema instead of dropping and re-creating the database.
I recommend to have look following link which makes you more clear about your problem.
https://msdn.microsoft.com/en-us/data/jj591621
I'm using MVC 5 with Entity Framework 6, automatic migrations are disabled, no seed is used and I'm scripting out my updates to production.
I'll hold up my hands and say I'm fairly new to MVC and EF.
I just uploaded a new codebase to production, and forgot that the model had changed. When I went to login to the new version, it threw and error page. Fine, I forgot to script the latest migration - I did that, hooked up to SSMS and found that the database was gone.
Slight panic, restore from backup (I'm not that daft!) and apply the migration and everything starts working as it should.
Why did my code delete the entire database when the model had changed? As said, automatic migrations are disabled and this behaviour doesn't happen on development machines, they throw an error about the model having been changed.
Edit to add: Whilst looking at the Initialisation patterns in Fernanda's answer, none of them say "Drop the database and then do nothing else". My database was dropped, the MDF and LDF gone, nothing is SSMS and nothing recreated in its place. If a blank database was created in its place I'd understand a bit more. That said, the user account had DBO on the database but not master, so would have been able to drop the database but not create a new one?
Read this about Database Initialization Strategies in Code-First:
http://www.entityframeworktutorial.net/code-first/database-initialization-strategy-in-code-first.aspx
Check your dbcontext initialization and be sure that the option DropCreateDatabaseIfModelChanges is comment
//Database.SetInitializer(new DropCreateDatabaseIfModelChanges());
I am working on a project which is using Entity Framework code first for its data structure. It was created with code first, but was never migrated again and only has its initial migration data stored. Since then, the database has been modified directly through server explorer in VS2015.
There is no migration information about any changes and the database has critical information which I cannot lose.
Which brings me to my Questions.
If I create a new migration and update the database from it, will it wipe all changes which were not recorded in migrations and still leave the changes which were made as well?
The details of your question is a bit sketchy, but I will make some assumptions in order to help you along. Please correct where I am wrong.
I assume that you want to keep the data which resulted from the changes which were effected directly to the database, but you do not want to keep the changes that was effected to the database - in other words: keep the data but not the datastructures.
My advice is as follows
Always perform a full backup of your database when you are about to do something you are uncertain about.
If you can identify the tables you want to update, you can always use the SELECT INTO statement to create a quick backup of the specific tables only. These tables will not be removed when you do a EF database migration unless you explicitly script the deletion.
You can build the SELECT INTO statement into your EF migration via the Sql() method, or you can manually run the command against the database.
More information:
Click here to learn about EF code first migrations in general
Click here for a comprehensive code first migration reference
I believe following two posts will help you.
EF 4.3 Migration Walkthrough : http://blogs.msdn.com/b/adonet/archive/2012/02/09/ef-4-3-code-based-migrations-walkthrough.aspx
update:
Code First Migrations with an existing database
https://msdn.microsoft.com/en-us/data/dn579398.aspx
My application has a one context that is injected using Autofac. I also have plugins which created and maintained their own contexts on the same database. I'm bringing it all in-line now so that the plugins just use the main context.
The issue I now face is that because the tables already exist in the database, I can't update-database because it says PluginTable already exists in the database. I can't do an add-migration and then remove the Up / Down entries because the plugins aren't within the same project.
Note: I think this is only an issue because the tables already exist so I need to get the current migration entries up to date so it doesn't try and recreate the tables.
Note: I considered re-building the migration file but again, the same problem will happen because add migration doesn't work.
I don't know what code to post that will help with this but I'm just wondering if we can tell ef to ignore tables that already exist on its creation process (this sounds daft as I type it but I'm not sure what else to do).
EDIT: Perhaps the question I should be asking is how to get the add-migration to take note of the other projects so I can just do a blank add migration and get the migration file up to date
Not sure what you mean by the can't add-migration, but if you need to run a migration to establish a baseline:
Add-Migration MyBaseline –IgnoreChanges
https://msdn.microsoft.com/en-us/data/dn579398.aspx?f=255&MSPPError=-2147217396#option1
The problem that when i change the new database then application not detected the new database and retreive error
The model backing the 'DBContext' context has changed since the
database was created. Consider using Code First Migrations to update
the database (http://go.microsoft.com/fwlink/?LinkId=238269).
but i don't using Migrations so i don't update-database by Package Manager Console
How can i fix this problem?
Actually it does detect changes in your database. The database differs from the model. The error message.
This error is thrown when the hash stored in the migrations history table does not match a calculated hash. (Have a look at __MigrationHistory table, might be under system tables)
If you delete this table the check is essentially disabled. You can achieve something similar by adding Database.SetInitializer<YourContextType>(null) to the startup of your application. The latter disables database creation from within that application, so if you want to create the database by code, you would need to do this from a separate application (for example an console app). I prefer to go this way for web applications.
Secondly: if you change your database manually (change columns, add tables, etc.) you need to adjust your model. So for each DDL statement, change your code.
If you are not using code first, you could update your existing model in the designer.
I ran into this problem when I first started with code first and mvc. the answer below is absolutely correct but you should go to the ASP.net website and do some tutorials on code first migrations. you need a better understanding how update database and initialize and migrations work.