It doesn't differ from reference fields. it is about automation distributed
transaction.
Table 'person' hasn't Field('alias_name' ) at db level, it's fake Field
with reverse reference declaration ( 'storedin alias_opt.alias_name' ) that
defines table.field that would be really involved in CRUD-process of table
'person'
On Wednesday, December 7, 2016 at 5:29:28 AM UTC+3, Dave S wrote:
>
>
> On Tuesday, December 6, 2016 at 3:41:38 PM UTC-8, Richard wrote:
>>
>> UP, never get any answer...
>>
>
> How would this differ from reference fields?
>
> /dps
>
>
>>
>> On Sat, Jan 23, 2016 at 4:08 PM, Val K <[email protected]> wrote:
>>
>>> Hi guys!
>>> I have an idea to improve DAL in scope of work with normalized DB.
>>> As known It's a common practice to avoid NULL value by creating separate
>>> (option) table(s) to store non required fields.
>>> So, it would be great to have a field type like "storedin
>>> table_name.field_name"
>>> For example:
>>>
>>> db.define_table('alias_opt', Field('name'), Field('alias_name', 'reference
>>> person'))
>>> db.define_table('person', Field('name'), Field('alias_name', 'storedin
>>> alias_opt.alias_name'))
>>>
>>> #INSERT:
>>> db.person.insert(name='Alex', alias_name='Macedonian')
>>> # means:
>>> id=db.person.insert(name='Alex')
>>> db.alias_opt.insert(id=id, alias_name='Macedonian')
>>>
>>> #UPDATE:
>>> db(db.person.id==id).update(... , alias_name=None)
>>> # means:
>>> # update person
>>> ...
>>> # update option table
>>> update_opt_args = filter_storedin_fields(update_args)
>>> opt_rec = db.alias_opt(id)
>>> opt_rec.update(update_opt_args)
>>> if not any(opt_rec.values()): # - all fields of option table record
>>> is None
>>> del db.alias_opt(id)
>>> else:
>>> db.alias_opt.update_or_insert(id==id, **update_opt_args)
>>>
>>> #DELETE:
>>> del db.person(id) also means del db.alias_opt(id), like ondelete=
>>> 'CASCADE'
>>>
>>> #SELECT:
>>> rows = db(db.person).select()
>>> # means:
>>> rows = db(db.person).select( left=[ db.alias_opt.on( db.alias_opt.id ==
>>> db.person.id ) ] )
>>> but only "storedin" fields should be selected from db.alis_opt
>>> and they should be accessed by row.alias_name (not only by row.
>>> joined_table.field_name )
>>>
>>> Considering, that table person could be a VIEW (i.e. JOIN is already
>>> performed at DB level), there is no need to make join at web2py level,
>>> it could be fixed by passing an option arg like is_view=True to
>>> define_table()
>>> I know, that behavior of insert/update/delete could be easy realized by
>>> custom class based on Table
>>> with a little hacking Field-class to intercept field type to fix it to
>>> web2py type ( considering person.alias_name.type ==
>>> alias_opt.alias_name.type ).
>>> But it's hard for me to change select() behavior, because there is only
>>> common_filter, but there isn't common_join/common_left with providing of
>>> maping (aliasing) joined table fields to 'storedin' fields.
>>>
>>> In fact, I dream of common_join depends on discriminator field, that
>>> will switch tables to be joined depend on discriminator value specified in
>>> the query (something like db.object.type_id==type_id),
>>> if descriminator is not specified or couldn't be resolved at web2py
>>> level, it performs left join all tables (from a list containing possible
>>> common_join tables)
>>>
>>> P.S. May be I try to reinvent the wheel, so feel free to shoot me!
>>>
>>> --
>>> Resources:
>>> - http://web2py.com
>>> - http://web2py.com/book (Documentation)
>>> - http://github.com/web2py/web2py (Source code)
>>> - https://code.google.com/p/web2py/issues/list (Report Issues)
>>> ---
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>>> an email to [email protected].
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>>>
>>
>>
--
Resources:
- http://web2py.com
- http://web2py.com/book (Documentation)
- http://github.com/web2py/web2py (Source code)
- https://code.google.com/p/web2py/issues/list (Report Issues)
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