I have uploaded my MVC3 project , it's s simple blog , at first it works well but after couple hours! following error appears (I've made custom error to Off to see the error)
The model backing the 'SiteContext' 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 DropCreateDatabaseIfModelChanges strategy will automatically delete and recreate the database, and optionally seed it with new data.
to solve this I have to manually delete my database and create again and then restore to the backup that I have created. but after after 2 hours again I get the error!
I really don't have any idea , what caused that ??
When you create a model and ask EF to create a database from it, EF would hash the model and store the hash value with the database. Whenever the context is created, EF recomputes the hash and matches it against what is stored at the database. If the model changes in any way, the resulting hash will be different and EF will throw the exception you have just seen. This is done in order to keep the model in sync with the database.
Is there any way the model could have changed during runtime?
One thing you could do to figure out the difference is to
1.Re-create the database from the model as you are doing now and get it scripted (script1.sql).
2.Wait till the error happens and delete the db and re-create it again and script it (script2.sql)
3.Try to compare the two and see whether you can spot a difference in the schemas.
This should give you an idea of what has changed in the model.
Goodluck
Related
I'm using VS2013 in a MVC 5 app. Created EF6 model using the database first approach which yielded the model as expected. Subsequently I will make changes in the database objects (tables, views, stored procs). When I go into the model to update it, the visible model will get updated. Looking at the Model Browser, I have to manually clean up the artifacts that no longer exist. Am I missing something in my procedure?
When you right click and update the model from the database, it will typically add new pieces automatically, but in my experience it doesn't automatically remove pieces that are no longer there, so you'll need to watch for those and delete them manually.
On the plus side, if you had any special customizations around a field (e.g. enum types), and the field gets renamed, this gives you a chance to compare the two configurations and make sure they line up before you delete the old field from your model.
I am getting error
"The model backing the 'ApplicationDbContext' context has changed since the database was created. Consider using Code First Migrations to update the database"
I could find few answers but i do lose my data.
I am using Identity 2.0.
What is solution to this?
Try to write:
Database.SetInitializer<ApplicationDbContext>(
null
);
into your Application_Start() method in the global.asax file...
(Rename the ApplicationDbContext name to the name you use in your application)
The problem is that you're working with a model that already created the tables, then you changed the model (but no the database), so when it goes and tries to work with the database there is a mismatch between the model and the database.
I don't know if you're working with code first or not, but I suggest you to MigrateDatabaseToLatestVersion initializer which will update the database automatically to match the changes in the model you've done without loosing data.
Hope it helps. Guillermo.
I am very new to EF programming.
My application gets the data from existing database. (DB first)
Now I have come to situation where I want to update my model to newer DB. basically the core schema is same as previous but has some modification in the table.
When I change the DB name for app.config and update the model it gives list of error
have I missed something?
When you do an update it merges the model you have with the DB that you update from. Additional columns are added to your existing entities but columns that you have removed from the DB are not removed from your entities and you need to remove these mappings yourself.
If you know which tables have columns removed it sometimes easier to delete the entity from your model and then do an update to reload it from the DB.
If you've don't know what tables or there have been many then it may be easier to delete all entities from your model and just do a full Update to reload the the new DB structure.
Basically, I have a LINQ database context and its model. As usually, I create the DB in the SQL context if the DB does not exist (the context is a singleton and on every access to it, this is checked).
Everything works well if I add data to the DB on the first launch. But if I don't insert any data during the first start of the app, on successive launches I get
SqlCeException:The specified table does not exist [TableName]
I don't know how more specifically I can explain it, but the exception comes immediately whenever I do a LINQ query on the second launch of the app if I don't insert any data on the first launch. If i do insert some data during the first launch, all is fine for the rest of the app's life time. Why would it be a bad thing to create the DBs and introduce the DB context, but not insert any data?
Here's my LINQ DB model:
https://github.com/kypeli/Podcatcher/blob/master/wp7/Podcatcher/ViewModels/PodcastSubscriptionModel.cs
Here's where I get the exception on second start if I didn't insert any data on the first launch:
https://github.com/kypeli/Podcatcher/blob/master/wp7/Podcatcher/PodcastSqlModel.cs#L64
It also strikes me that there's no API call to check if a table exists or not in LINQ, so I would have to assume "this should just work" - but it doesn't.
Any ideas? Thanks! :)
Update: I verified analyzing the .sdf file that indeed there are no tables created if I don't insert any data upon first launch of the app. As I see it:
This is a bug in LINQ-to-SQL. It should not crash if there are no tables present, but know that it should create them. Or deal with the case and create tables only when data is inserted.
I would need to insert some dummy data into SQL always on first launch, or...
Check if a table exists, if not, react to it by forcing LINQ-to-SQL to create them. But how?
I've dealt with this problem also, I've fixed it this way:
get the data context:
dbDataContext = new DBDataContext(DBConnectionString);
if( dbDataContext.DatabaseExists() == true)
//then try to get an entity:
System.Data.Linq.Table<Entity> entities = dbDataContext.Tablename;
//try to get an element from the entity:
IEnumerator<Entity> enumEntity = entities.GetEnumerator();
entities.GetEnumerator(); will always raise the exception "Table not found."
Just use a try/catch and in the catch scope delete the db and recreate it, because your DB is empty anyway :)
dbDataContext.DeleteDatabase();
dbDataContext.CreateDatabase();
dbDataContext.SubmitChanges();
I have an existing MVC3 application and database that is on a SQL Server 2008 R2 and I had to add a bool item to an existing model.
After I added it to the model, I rebuilt and published the project. Then I opened up SQL Server Management Studio and went to the table and added the entry to the column as a bit, I had to make it nullable since the table already contains data.
I thought this would be all that I would need to do to get everything working. However I got this error:
The model backing the 'psllc_DB' 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 DropCreateDatabaseIfModelChanges strategy will automatically delete and recreate the database, and optionally seed it with new data.
I'm not sure what else to do, I went back to the code and changed the bool to bool? so it will be nullable but this didn't help either. I can't drop the entire database since it's full of data, however as a last ditch possibility I could drop this table and re-create it cause it only has a few entries, but I don't know if that will work. I'm not sure what else to do so any advice would be very appreciated.
Update
Since I'm not getting any responses, let me rephrase my question.
How should I update my database (a SQL Express mdf file) to add a bool Column to a Table that has data already? I need the database to match my updated MVC 3 Entity Code First model otherwise I get the above error.
Thanks
Since this is code-first, you should do this code-first: change the class and use EF-migrations to change the database. The way you do it, the model and the database may match, but the meta information in the database is not updated.
By the way, if you supply a default value, you can add a non-nullable column.