Refactoring: store and db-views

[ghost]

Currently, store and db-views are imported in several Powerline modules. There should be one single module that contains all the dependencies to the other gg modules (db, messaging) to achive more loose coupling.

[warren-oneill]

:+1: good idea

[ghost]

@warren-oneill Basically, what I would like to do is:

1. Introduce a new module for powerline that contains all dependencies from gg.database. All powerline modules requiring db access then would import store etc. from this module. The same applies to the messaging.

2. Introduce a prefix + classname naming convention, e.g. EEXMetadata, EEXSource, EEXExchange, where not yet done in that way. EDIT: I see thats done, except for the DataGenerator class

   3. Refactor assets, exchanges and sources by introducing a simple factory pattern. E.g. you could do exch = Exchange('EEX') rather than exch = EEXExchange(). By using the naming convention in (2.) the Exchange class creates the relevant objects, i.e. acts as a factory.

I have some code and ideas for the items above I will present in our meeting on Friday.

[warren-oneill]

1) makes sense 2) Isn't that what I do? the only difference I can see is my prefix is not all caps. 3) whats the advantage of using this method?

[ghost]

@warren-oneill As we talked in our meeting, the scope of the refactoring focus on a strict separation of all db and query stuff from the exchange, metadata and source classes, including a clean use if session (see also: http://docs.sqlalchemy.org/en/latest/orm/session_basics.html#what-does-the-session-do ). Refactored code is in a separate branch.

[ghost]

Refactoring includes:

• flatter package hierarchy
• code restructured in a more use-case (or exchange) oriented fashion
• separate query modules for each use-case (or exchange)
• basic settings file for database, amqp etc. configurations
• a simple store manager that:
  • creates a store object of the store class given in the settings file
  • dynamically imports query methods

Still TODO:

• decision: merge yes/no
• rewrite and improve unit tests, add doc strings (I would like to do this after the decision as it involves quite some work)
• merge