How to call foreign relation model Pluggable to other model Pluggable in turbogears 2.3.11?

Question

I used Turbogears 2.3.11. I have 1 application and 2 Pluggable Applications with TurboGears. In Pluggable Applications have own models. How to call model in one Pluggable Application from two Pluggable Application?

In example:

- mainapp
  -- model
     --- __init__.py
     --- auth.py
- plugapp_one
  -- model
     --- __init__.py
     --- models.py
         ---- Book
- plugapp_two
  -- model
     --- __init__.py
     --- models.py
         ---- Buyer
         ---- Card

In Card Object call relation to Book Object, I use app_model.Book. It error

AttributeError: 'module' object has no attribute 'Book' 

My Code in models.py of plugapp_two

from tgext.pluggable import app_model, primary_key

class Card(DeclarativeBase):
    __tablename__ = 'card'
    uid = Column(Integer, autoincrement=True, primary_key=True)
    name = Column(Unicode(16))
    id_book = Column(Integer, ForeignKey(primary_key(app_model.Book)))
    book = relation(app_model.Book)

Answer 1

You have two choices:

1. Explicitly provide the Model at plug time, usually in the form like package.module:Model. Much like tgapp-resetpassword does for its forms: https://github.com/axant/tgapp-resetpassword#plugin-options. Then wherever you need to access that model you access the one specified there. The hard part is that you must ensure that every place that accesses that Model accesses it lazily, or you might end up trying to use it before it was configured. See LazyForeignKey https://github.com/TurboGears/tgext.pluggable#relations-with-plugged-apps-models

2. Option 1 is surely the most flexible as you choose which model is related at plugin time, but in case you are using pluggable apps just to split your own application and don't plan to reuse them you can just plug them all with global_models=True option and all the models from the pluggable apps will end up being available in tgext.pluggable.app_model.Model.

Note that both solution need to pay attention to when you access the model, as it might have not been plugged yet. You should try to delay model usage as much as possible through LazyForeignKey and relationship with lambdas, such that the model is only used when actually needed. Or you might end up trying to access it before it was plugged.