Rails core - Apr 2013 - Proposed new ActiveRecord feature: Built-in "orphaned" scope for AR objects

For purposes of maintenance and data cleanup, sometimes it is helpful to 
determine if you have orphaned records in your AR backing store.

Assuming that an AR::Base descendant has one or more belongs_to 
associations, I propose the addition of built-in 
"<association_name>_orphaned" scopes that would return the set
of records
where the belongs_to association record doesn''t exist. Using
association
introspection, this would be fairly straightforward.

However, I''m not certain about the idea of having a
"built-in" scope, as
I''m not sure if any even exist at this point. Is this better
implemented in
a standalone gem that would then add these scopes?

Many thanks,
Wes

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Hey Wes,

If you use foreign key constraints, then all orphaned records would have
the foreign key set to null. If not, you''d have to do an outer join to
determine what is orphaned. Given this divergence, IMO this is best left to
the author.

-Ben


On Mon, Apr 8, 2013 at 2:57 PM, Wes Gamble <weyus@att.net> wrote:
> For purposes of maintenance and data cleanup, sometimes it is helpful to
> determine if you have orphaned records in your AR backing store.
>
> Assuming that an AR::Base descendant has one or more belongs_to
> associations, I propose the addition of built-in
> "<association_name>_orphaned" scopes that would return the
set of records
> where the belongs_to association record doesn''t exist. Using
association
> introspection, this would be fairly straightforward.
>
> However, I''m not certain about the idea of having a
"built-in" scope, as
> I''m not sure if any even exist at this point. Is this better
implemented in
> a standalone gem that would then add these scopes?
>
> Many thanks,
> Wes
>
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>
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Ben,

Depending on how things are set up, you may or may not have NULL values in 
the foreign key column. In either case, this query:

Given:

  X: an AR::Base descendent class
  association_class: the belongs_to association class (discovered via 
association reflection)
  foreign_key: the foreign key to the belongs_to association class 
(discover via association reflection)

X.where("{foreign_key} NOT IN (SELECT {association_class.primary_key} FROM 
{association_class.table_name})")

will give you all orphaned records for X with respect to association_class.

W

On Monday, April 8, 2013 5:45:16 PM UTC-5, Ben Woosley
wrote:
>
> Hey Wes,
>
> If you use foreign key constraints, then all orphaned records would have 
> the foreign key set to null. If not, you''d have to do an outer
join to
> determine what is orphaned. Given this divergence, IMO this is best left to
> the author.
>
> -Ben
>
>
> On Mon, Apr 8, 2013 at 2:57 PM, Wes Gamble <we...@att.net
<javascript:>>wrote:
>
>> For purposes of maintenance and data cleanup, sometimes it is helpful
to
>> determine if you have orphaned records in your AR backing store.
>>
>> Assuming that an AR::Base descendant has one or more belongs_to 
>> associations, I propose the addition of built-in 
>> "<association_name>_orphaned" scopes that would return
the set of records
>> where the belongs_to association record doesn''t exist. Using
association
>> introspection, this would be fairly straightforward.
>>
>> However, I''m not certain about the idea of having a
"built-in" scope, as
>> I''m not sure if any even exist at this point. Is this better
implemented in
>> a standalone gem that would then add these scopes?
>>
>> Many thanks,
>> Wes
>>
>> -- 
>> You received this message because you are subscribed to the Google
Groups
>> "Ruby on Rails: Core" group.
>> To unsubscribe from this group and stop receiving emails from it, send
an
>> email to rubyonrails-co...@googlegroups.com <javascript:>.
>> To post to this group, send email to
rubyonra...@googlegroups.com<javascript:>
>> .
>> Visit this group at
http://groups.google.com/group/rubyonrails-core?hl=en
>> .
>> For more options, visit https://groups.google.com/groups/opt_out.
>>  
>>  
>>
>
>
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