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.
Related
I have an SQL database with 200 tables.
I changed the primary key on one "basic" table.
I changed ALL foreign keys referring to that table, in more than 20 tables.
I Updated the LinQ model (right-click, update model from DB) to reflect the changes in the model itself.
As a result, 3 tables disappeared from the model (they are not visible in the graphical view of the model), and I get errors: Error 3013: mapping problem from line xxxx: no mapping fot table "tablename"
Trying to update again, if I look on the details of the tables to add, I can't see the 3 tables "lost": they are in the DB, I'm sure, and SEEM to be in the model, because they aren't in the list of tables that I can add, but they aren't in the model.
What could I do in this situation?
It seems solved ... one friend suggested to open manually the edmx file with an editor (I used Notepad++), and remove any reference at the 3 tables (they were there), save, and try the update again, and the tables appeared again.
i'd like to know if it's possible at all to update the table schema in a Migration through a specific Eloquent Model, or if i actually need to pass in the name of the Table and Connection every single time.
I ask this because in my case this requires an additional configuration file that my package must publish to the end users, apart from the already required table Eloquent model (which is used for other purposes)
You can update schema later and add or drop columns and/or index.
To do this you create a new migration and add the changes there. It will change the table over your previous version.
More info in Laravel documentation.
For renaming the table
Schema::rename($from, $to);
https://laravel.com/docs/5.2/migrations#renaming-and-dropping-tables
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
I am using Database First EF to generate model from the existing database. When I first generated the models, it ignores only one of the table, the entity was not added to EDMX, no model file is created for the table and no context is created for the entity.
When I tried to explicitly add the table to EDMX (when generating the model, selected the specific table first and then updated the model with all the other tables from the database), it complained with the following error.
Two entities with possibly different keys are mapped to the same row. Ensure these two mapping fragments map both ends of the AssociationSet to the corresponding columns.
This specific table has two columns which are primary keys of some other tables and both the columns are specified as Primary keys for the table.
Am I doing something wrong or should I handle this table differently since it has two columns defined as Primary Keys? Any suggestions greatly appreciated!
You are not doing anything wrong. Your table is junction table for many-to-many relation. You don't need that table in the model because EF (in contrast to database) can handle many-to-many relation directly without any intermediate. The table is actually mapped on behind of the many-to-many relation - you will see that in mapping details window.
Btw. you are not using code first. Code first = no EDMX.
When I delete a column from an already existing db from an already existing database model, right clicking on the .edmx "Update model from Database" does not remove deleted columns from the model (column existed in the model and db before but was removed from db) .
One thing that I have noticed is that my mapping detals are not matching up with my .edmx. Mapping detals are up to date with database but they dont' match that of the .edmx.
Is this expected behavior? Thanks!
[Using asp.net 4.0/EF4.1]
I have found that, when I update the underlying database table, the best approach is to delete the mapped table from the edmx designer, and then do Update Model from Database.