LINQ to SQL: Multiple / Single .dbml per project?

Question

I've read Rick Strahl's article on Linq to SQL DataContext Lifetime Management hoping to find some answers on how I would manage my .dbml files since they are so closely related to DataContext. Unfortunately, Rick's article seems to be focused on DataContext lifetime at runtime though, and my question is concerned with how the .dbml's should be organized at design time.

The general question of 'Best practices with .dbml's' has been asked and answered here, and the answers have focused on external tools to manage the .dbml.

I'm asking a more focused question of when and why should you not have a single .dbml file in your LINQ to SQL based project?

Answer 1

Please note that LINQ2SQL is intended for simple and easy way to handle database relationship with objects.

Do not break table relationship and units of work concepts by creating multiple .dbml files.

If you ever need to create multiple .dbml files (which i don't recommend), then try to satisfy the following:-

1. If you create multiple databases with no relationship between those database tables.
2. If you want to use one of these .dbml just to handle stored procedures
3. If you do not care about unit of work concept.

If your database is too complex, then I would consider ORM such as NHibernate, EF 4

Answer 2

In my opinion, you can split the .dmbl files so that each hold a subset of tables/procs from a DB according to function and relationship. I have not done this yet so this is just opinion.

I have however created multiple .dbml files to assist with unit testing. If you work in an environment which restricts you to using stored procs in your production environment then you cannot use the table part of the .dbml (you can use the proc part though). So if you "unit test" (this is really integration testing) the DB layer of your code you can call the proc wrapper and then check the results by querying the tables through the .dbml interface. In cases like this I'll split the .dmbl file into just the tables that I want to query in my "unit test."

Further info: I have 2 solutions that I build. One has unit tests and is never built on the build server. The other is built on the build server and deployed to test/production.

Answer 3

I'd say, you always just need 1 dbml-file PER database. If you have multiple connections to other databases, consider design or use seperate dbml-files. Either way, one is enough per database.

This because the dbml mapps to your tables and why not just use one "data connector" / "data layer" for that, seems odd / weird design to use more than one.

It's probably more controllable using only 1 aswell.