вторник, 31 июля 2012 г.

EF Migrations: database schema maintenance burden solved? … Not really.

Just a couple of quick notes about EF Migrations [with ‘code first’ approach]. It sounded like EF Migrations were going to solve all the problems around database development process and allow all the magic to happen right inside Visual Studio. A lot of magic is happening under the hood indeed, but it does not seem to be able to let us forget about sql scripts once and forever (it’s not that I ever believed it really will Winking smile).

First comes a task of deploying a database. We can have a connection string in [web].config, and in case the database is empty, it will be populated by applying all migrations right from the start (starting from Initial). It works ok unless you have some [initial] data to be present in the database upon first launch of the application. You might argue that this is a problem of deployment, not EF Migrations itself, but wait a minute – how are we supposed to deploy a database without a [sql] script? Ok, EF Migrations give you an option for creating a sql script rather than applying a particular migration to an existing database. But there’s a trick – you still have to have a database in place in order to do this. I’ve found it a bit annoying [and frustrating] to have to create an empty database just for getting migration scripted – Update-Database does not work without a connection string. I wish it could fake it.

Ok, you’ve done your homework and now you have an empty database to deed Update-Database with. My first intention was to let EF Migrations to script the latest state of the schema for me [by applying all the migrations one by one]. I issued

Update-Database –script –ConnectionString “[my connection string]”

and got a script (finally!). But guess what? It was not working – due to the fact that EF Migrations does not put each migration into a separate batch, it got a number of very simple syntax errors (declaring a variable multiply times). It does not take long to fix it, but in general it does not look reliable enough for me to trust it.

I ended up with scripting only ‘Initial’ migration and letting EF Migrations do the rest of schema update (with initial data already in) upon first launch of the application. This leaves [me] an open question, however: what if we need to start developing ‘version Next’ and start with the database of the current one? Sure, we can script it into ‘Initial’ in new project. Or just make a branch and continue development having all the migrations from the previous version. Both options does not look great in terms of maintenance.

Despite these little issues, EF Migrations are a huge step ahead and I see that employing code-first approach simplifies life for both app and db developers – less sql to produce/review/maintain.


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