I have played with Entity Framework 4.3 migrations for some time now, but I have trouble achieving the next behavior: In case my code runs on an existing database, I want the database to be migrated automatically to the latest version, but in case the database doesn't exist, the database should be created automatically from the migrations.
I think the problems is related to the first migration that you create. If you create the first migration using -IgnoreChanges parameter (or manually delete them as explained here: http://thedatafarm.com/blog/data-access/using-ef-migrations-with-an-existing-database/), you will not be able to use migrations in order to create a new table using the DbMigrator class. because you don't have the initial migration. If you create the first migration without using -IgnoreChanges, than the migration of the existing database will not be possible. Does anybody has any solution for this problem?
So you have existing database and you want to use migrations on that database and in the same time you want to support database creation by migrations in case of new deployment?
It looks like little bit unsupported use case. The simplest in this case (not tested) would be either conditional compilation or conditional migration driven by some AppSettings key. It means creating initial migration as if you don't have the database and modify Up method to:
public override void Up() {
if (ConfigurationManager.AppSettings["NewDatabaseRequired"] == "true") {
// Here is generated content
}
}
or
public override void Up() {
#if NewDatabaseRequired
// Here is generated content
#endif
}
There is plenty of other more complicated options including scripting your current database, modify the script to end if tables already exist, add a script as a resource to your migration assembly and execute the script in the Up method generated with -IgnoreChanges.
As another option you can open additional database connection and check if tables from migration already exists (by querying sys.tables view in SQL Server). This will not need generated script.
Related
I'm using Sequel::Model. My model has a set_schema block and a create_table call, so the database is completely managed by the model. The database is sqlite.
I'm trying to add columns to the database and I can't find a way to. Adding fields to the schema has no effect. Adding a migration or an alter_table call doesn't do anything. I've asked on IRC and read the docs. I can't find an example of anyone doing this, but it seems simple.
How do I add a column/field to a Sequel Model?
I did a bunch of research and talked to Jeremy Evans. I was going about this wrong. The right way to do this was to remove my schema plugin code and create_table block and move to using migrations. The steps I went through were:
Remove the schema code (create_table, set_schema) from my modesl
Dump the schema from my current sqlite data files into initial migrations into migration files via the sequel -d command
Create a new migration that adds the columns I need via add_column calls in an alter_table block in a change block
Apply the migrations via the sequel -m command
Create rake tasks to run the migrations and hook those tasks into my deploy tasks
Im using code-first to create a database. And now im trying to make a linq expression to get data out of the database but then i get this error:
"The model backing the 'FantasySport' context has changed since the database was created. Consider using Code First Migrations to update the database"
So i go to package-manager console and types update-database and it says that there is nothing to update.
"PM> update-database
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
No pending code-based migrations.
Running Seed method."
----EDIT------
Here is the initializer method:
private class SimpleMembershipInitializer
{
public SimpleMembershipInitializer()
{
Database.SetInitializer<UsersContext>(null);
try
{
using (var context = new UsersContext())
{
if (!context.Database.Exists())
{
// Create the SimpleMembership database without Entity Framework migration schema
((IObjectContextAdapter)context).ObjectContext.CreateDatabase();
}
}
WebSecurity.InitializeDatabaseConnection("DefaultConnection", "UserProfile", "UserId", "UserName", autoCreateTables: true);
}
catch (Exception ex)
{
throw new InvalidOperationException("The ASP.NET Simple Membership database could not be initialized. For more information, please see http://go.microsoft.com/fwlink/?LinkId=256588", ex);
}
}
So what is the problem?
You first have to add a migration to update to. You can do it by typing the following command in the package manager console:
add-migration "a custom name for your migration here..."
This will cause a migration to be created, after which you can run the Update-database command from the package manager console.
[EDIT]
The Database.SetInitializer method specifies the strategy for creating and seeding your database on the fly. Since that is what is causing this error, and since we are manually creating and seeding your database through the update-database command, we want to turn it off. http://www.codeguru.com/csharp/article.php/c19999/Understanding-Database-Initializers-in-Entity-Framework-Code-First.htm
To be able to update the database through migrations you have to use the
add-migration "<migration-name>"
command however I've experienced it getting "stuck" sometimes meaning that you will get this error or it will display the usual message that there is a need for another migration step. To solve this make sure that
there is no hidden migration file which was not deleted just removed from the project
always build the project after an add-migration command before issuing the update-database command
make sure the connection string to the database is the same in the project you issue the update-database command points to the same database your program uses.
Other than this you can check whether the __MigrationHistory table contains all the migration steps including the newest as the Entity Framework tests the current model against this table's records.
Some of these voodoo (like rebuilding and cleaning) was only required around EF 4.4 I guess the update-database script was improved in this area as well.
I'm a bit lost how I should get the entity framework to work with automatic migration. I want:
The database to be created automatically when it doesnt exist
The database to be updated automatically when the model changed
For the latter I'm using DbMigrator. It is rather slow so I don't want to run it every request, and also I have multiple databases in the same application so it cant go in Application_Start which is why I put it in Session_Start like this:
if (Session["started"] == null)
{
// this takes care of any database updates that might be necessary.
MigrationConfiguration configuration = new MigrationConfiguration();
DbMigrator migrator = new DbMigrator(configuration);
List<string> pm = migrator.GetPendingMigrations().ToList();
if (pm.Count > 0)
{
migrator.Update();
}
}
else
{
Session["started"] = "started";
}
Not sure if this is the right way to do it but it seems to work, however it doesnt actually generate the database when it doesnt exist. It gives me a "Cannot open database "db" requested by the login"
I had this working before with the following:
Database.SetInitializer<DbContext>(new InitializerIfModelChange());
This drops the database and generates seed data which is fine for when the database doesnt exist but it also is triggers when the database is changed (in which case I would like DbMigrator to handle it) This was in Application_Start before but I'm not sure what to do with it. I'm afraid that it will conflict with the DbMigrator. How would I set this all up in order to achieve the two things described earlier?
I manually run the Update-Database in the package manager whenever the database needs to be changed. Initially I used the Database.SetInitializer like you did to create the database but have it commented out now.
Checkout Entity Framework 4.3 Automatic Migrations Walkthrough for more advanced help.
This should work for what you want, then if you need to create a new database just add Database.SetInitializer<NewDBContext>(new NewDBInitializer()); like you had, build and run. Then comment it out so it doesn't run in the future on a model change and instead use the Update-Database command in the package manager.
In Models context file it was mentioned
If you want Entity Framework to drop and regenerate your database
automatically whenever you change your model schema, add the following
code to the Application_Start method in your Global.asax file. Note:
this will destroy and re-create your database with every model change.
System.Data.Entity.Database.SetInitializer(new System.Data.Entity.DropCreateDatabaseIfModelChanges<HMS.Models.HMSContext>());
so I added this code in the Global.asax file inside protected void Application_Start().
Adding this line drops whole database when I do any changes in model class. Is there any alternate way to avoid this and still I can do Model changes?
i.e After performing changes in model when I rebuild and run my application, it drops my database and regenerate all the empty model tables. So I loose all my entered data and I want to preserve table data.
If you're using EF Code First 4.1, then, no, it will only drop and recreate. EF version 5 apparently supports dynamically changing the underlying database. It's in beta at the moment, but is available for production use if you want to try it out. You can install it through NuGet.
Suppose I have a database containing 3 tables in a grails application:
User
Activity
Friend
User table table has one to many relation to Activity and Friend tables so in User table I have:
static hasMany = [activies: Activity, friends: Friend]
and in Friend and Activity I have:
static belongsTo User.
Application is deployed and lets says thousands of customers have registered. Now changes are made in the database: Table Activity is dropped. A table Journal is created which is on the many sides of the User table. The User table has a new column added and this column cannot be null. An old column in Friend table is deleted that was also defined as not null.
So given above scenario and assume using MySQL what needs to be done to make above changes without deleting existing customers data and safely add the new table to existing customers?
Ruby on Rails comes with ActiveRecord for database migrations. Does Grails comes with something like this out of the box?
Currently in development when I run my grails application after adding a new not null column to a table, I get column cannot be null exception thrown unless I delete that table in the database before running grails application which would recreate the table if not exists. Obviously once the application is deployed I will not have the luxury to delete the table.
Unfortunately, the current version of Grails doesn't come with database migration. However, there is a plugin for Liquibase which makes migrations possible.
The next version of Grails (1.4, planned for Q1 2011) will supposedly contain a built-in migration tool, which I am very much looking forward to.
Note: I haven't used the Liquibase plugin, so I don't have any firsthand experience with it. I have seen numerous blog posts describing its use, however, and I'm probably going to use it in my next Grails project if 1.4 isn't out by then.