Cross-table linking

Some way to have models reference models. One-to-one, one-to-many, and many-to-many should be supported.

Since we don't have the benefit of a SQL database, we'll have to consider the following:

• Save and sync actions should probably not propagate
• Backrefs are possible, but...hard. Maybe add those later?
• Query/model option to eager-load referenced models
• What happens if a value is set but the object doesn't exist in the DB? None? AttributeError?

Hi steven! Has there been any progress in this area? I've been using this library for a while now, and am pretty happy with it. Thanks for taking the time to write it!

To get the conversation started, how about we consider something like this:

class RefType(TypeDefinition):
    type = dict
    aliases = ['ref'] # alternate names that reference this type
    ddb_data_type = MAP

    def coerce(self, value, force):
        # How do we type check a model?  issubclass(value, Model)?
        return value

    def ddb_dump(self, value):
        # Somehow get the parent model's key
        return self.model.meta_.pk_dict(results[-1], ddb_dump=True)

    def ddb_load(self, value):
        return engine.get(self.model, **value)

We probably want to do something with Field... perhaps derive a RefField? in order to hide a lot of this.

Anyway, this is just off the top of my head ATM. I know I'm already running into this in my own project, and I have to run through a chain of queries (saving off only the hash_key). Would be nice to use some of the optimizations like batched queries, etc...

I have the start of a Reference field located here. @stevearc I could really use your help with the caching. I have unittests that shows what I'm having trouble with. Any help would be most appreciated!

@stevearc or anyone else that is interested... I now have a working Reference field that correctly loads, saves and deletes (including cascading deletes) located here. It would be really nice if I could get some peer review, and perhaps move it into the core library, but for now it should work as stand alone package.