I am building a sinatra web app with a sequel database backend. The primary tasks of this app is collecting status messages from different robots, store them in a database and provide various methods to view them. A common denominator in these messages is, that they provide a WGS84 position in lat/lon.
Now I want to provide various filters for querying messages based on their positions, but I want to write these filters only once, test them only once but re-use them in all model-classes with a lat/lon entry.
To boil it down to a very simple example:
Sequel.migration do
up do
create_table(:auvmessages) do
primary_key :id
Float :lat
Float :lon
String :message
end
create_table(:asvmessages) do
primary_key :id
Float :lat
Float :lon
Integer :chargestate
end
end
end
class Auvessage < Sequel::Model
dataset_module do
def north_of(lat)
self.where{ latitude > lat}
end
end
end
class Asvessage < Sequel::Model
dataset_module do
def north_of(lat)
self.where{ latitude > lat}
end
end
end
In both model classes have north_of(lat) to filter for messages which originate north of a given latitude. This function is fairly simple and you can easily repeat it two or three times, but what about more complex cases?
I have played around a bit with modules outside of dataset_module but nothing seem to be right.
Is there a preferred way how to re-use filters over different models? I have searched a lot, but didn't find any satisfying answer.
Edit:
To make my question a bit more precise: I want to move all functions like north_of(lat) (there are a lot more) into a service class. What I want to know now, is the best way to integrate that service class into a sequel-model:
You can pass an existing module to dataset_module:
module NorthOf
def north_of(lat)
where{latitude > lat}
end
end
Auvessage.dataset_module NorthOf
Asvessage.dataset_module NorthOf