On May 8, 4:07 am, Stefan <[email protected]> wrote: > Hello, > > I have two questions. > > First question: How can I subclass Sequel::Model without having DB > connection?
You don't. Well, you can hack the internals and do so, but I won't support that. > When I do: > > class ETLJobSchedule < Sequel::Model > ... > end > > I get: > > /Library/Ruby/Gems/1.8/gems/sequel-3.11.0/lib/sequel/model/base.rb: > 125:in `db': No database associated with Sequel::Model (Sequel::Error) > from /Library/Ruby/Gems/1.8/gems/sequel-3.11.0/lib/sequel/model/ > base.rb:191:in `inherited' That's by design. > I do not know DB connection at the time of Class *declaration* and I > would like to set it up later, for example like this: > > ETLJobSchedule.set_dataset(@connecti...@etl_schedules_table]) The model class isn't usable until the database connection has been established. Connect to the database first, then load your model classes. > Second question: How can I have model instances from different > connections? You can have model classes with separate database connections: class ModelA < Sequel::Model(DB1[:table1]) end class ModelB < Sequel::Model(DB2[:table2]) end The Sequel::Model method takes any dataset, so it's easy to specify that the model class should use a specific database by giving it a dataset from that database. If you meant how to get two model instances from the same class to connect to different Database objects, you can't. > Example situation: I have more DBs or DB schemas with a table with > same structure. How can I use Sequel::Model with more connections > where the same structure exist? For that, look into Sequel's sharding functionality: http://sequel.rubyforge.org/rdoc/files/doc/sharding_rdoc.html However, sharding is more of a dataset feature, and while models have full support for sharding when retrieving records, there isn't any built in support for saving records to specific shards. It's probably not hard to add if you need it, though. > Two entry points for specifying connection are sufficient for me: one > factory method (that creates model instances) and method for selecting > objects (find). > > Something like: > schedule = ETLJobSchedule.new_from_connection(@connection) > schedules = ETLJobSchedule.find_using_connection(@connection, ...) That's not how Sequel works. You don't deal with connection objects, and while Sequel does make them available if you need them for low level stuff, there's no Sequel methods that accept them as arguments. You can do something like: schedules = ETLJobSchedule.server(:shard_id).first(...) To retrieve schedules from a specific shard. However, the new_from_connection can't be duplicated without some small extensions. Currently you'd need to override Model#_insert (kind of large), but I'd be OK with refactoring so that you'd only need to override a new method like _insert_dataset. For updating and deleting records, you would have to override _update_dataset and _delete_dataset. The only issue there is that Sequel does not store which shard was used to retrieve the objects. For that you could use the tactical_eager_loading plugin, and call retrieved_by to get access to the dataset that was used to retrieve the object, and get the shard id to use in _update_dataset and _delete_dataset. > Something analogous to Core Data where you can have more object stores > for one object model. I'm not familiar with Core Data. Anyway, hope this helps. If you have more questions, just respond. Jeremy -- You received this message because you are subscribed to the Google Groups "sequel-talk" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sequel-talk?hl=en.
