How to use Migrations the right way?

Hi,

can you provide an example on how to use your Migration-feature the right way please?

What I like to know is:

• am I right, that your Migration feature is used to give me e.g. the diff from my developer status database to a reference database, let's say the production database?
• when I do a "migration", I get a diff source (file), right?
• how to I use this file in a best practice way to run the migration on the target database, let's say from or within a VS setup?

Thanks!

No, the Migrations feature gives you a diff from your current model to the previous version of your model. It doesn't look at your databases at all. For example, suppose you create a new model, add an Order entity, and create a migration. Since there is no previous migration, that migration will include code for creating and dropping the Order table. Now suppose you add a Customer entity and an association, and create another migration. The designer compares your model to the previous migration, which only had an Order entity, and creates a migration with code for adding and dropping the Customer table and the Order.CustomerId foreign key. Notice that no databases are consulted, because you may not have created a database yet -- the only comparison is between snapshots of the model.

When you do a migration, you get a C# or Visual Basic file containing code to upgrade the database schema from the previous version of model to the current version of the model (and to roll back that change). The code is in the form of a class that inherits from our Migration base class. You can freely edit this code for example to perform data migration, set up reference data, etc. The files representing all the Migration classes for a single model, from the very beginning to the very latest version, are compiled together into a DLL.

You can then run the migrations in the following ways:

• From the command line using nhmigrate.exe
• From within Visual Studio by using the Migrations > Run Migration command - directly against a database
• From within Visual Studio by using the Migrations > Run Migration command - to generate a SQL script that can be run separately through your database's SQL command line tool
• By hosting the migration runner within your own application

Does that clarify things? Please do ask if you need more info!

Hi Ivan,

thanks, a great explanation!

Btw. how is the manual going? ;-)

Thanks, Kay

Uh, about as well as the screencast... * cough *

There is a help file available for the designer -- unfortunately it's not very visible because we can't install it via the Extension Manager, but you can download it or read it online at http://www.mindscapehq.com/products/nhdesigner/documentation. It does include several pages on the migrations feature but we agree there is room for improvement!