Relation.join behaviour

[halfAPI]

join result

On a class that uses FKEYS property, when we use join you have different kind of result depending on how many field names you specify.

Steps to reproduce :

> Class1().join([Class2(), '_foreign', ['id']])
{
 ...
 _foreign: ['my-super-id'],
 ...
}

> Class1().join([Class2(), '_foreign', ['id', 'label']])
{
 ...
 _foreign: [{
    'id': 'my-super-id',
    'label': 'helloworld'
 }],
 ...
}

This inconsistency of results may lead to errors.

What I'd advice is to have two join functions with the following signatures :

join([ rel: Relation(), fkey: string, field: string ], ...)

that would give a (field-type) list under the fkey attribute of the result

AND

join([ rel: Relation(), fkey: string, fields: string[], ...)

that would give a dictionary list under the fkey attribute of the result.

fkeys that point to primary keys

A feature that could be interesting would be for foreign keys that point to an id. We could have the "joined" object directly in the property instead of have a list of one object.

[joel-m]

join currently doesn't work on reverse fkeys. I've got a patch ready but I need to write some tests before releasing it.