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David Scheffel

2006-Dec-28 12:50 UTC

How to hide a database column from ActiveRecord?

Hi there!

I''ve added an array column to one of my tables for providing a faster
search. This column is populated by a trigger-function from a
detail-table. However this data is being overwritten with blank values
by ActiveRecord when performing an insert or update.

Can I tell ActiveRecord to ignore this column and not to add it to the
Attributes array?

Thanks..
David

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Phlip

2006-Dec-28 13:21 UTC

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Re: How to hide a database column from ActiveRecord?

David Scheffel wrote:
> I''ve added an array column to one of my tables for providing a
faster
> search. This column is populated by a trigger-function from a
> detail-table. However this data is being overwritten with blank values
> by ActiveRecord when performing an insert or update.
>
> Can I tell ActiveRecord to ignore this column and not to add it to the
> Attributes array?
Add an SQL View object and point the ActiveRecord at that.

(Hypothesis: ActiveRecord might not support your feature because it knows 
you can do the View trick.)

Or maybe not. ;-)

-- 
  Phlip
  http://www.greencheese.us/ZeekLand <-- NOT a blog!!! 


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David Scheffel

2006-Dec-28 16:10 UTC

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Re: How to hide a database column from ActiveRecord?

> Add an SQL View object and point the ActiveRecord at that.
> 
> (Hypothesis: ActiveRecord might not support your feature because it 
> knows
> you can do the View trick.)
> 
> Or maybe not. ;-)
But could I still use that "hidden" column in a call to find_by_sql? I
mean since it is not part of the underlying (the view) anymore?

Thanks
David

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Chris Gernon

2006-Dec-28 16:50 UTC

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Re: How to hide a database column from ActiveRecord?

I believe attr_protected would be a more straightforward way to 
accomplish this:

http://api.rubyonrails.com/classes/ActiveRecord/Base.html#M000873

"Attributes named in this macro are protected from mass-assignment, such 
as new(attributes) and attributes=(attributes). Their assignment will 
simply be ignored. Instead, you can use the direct writer methods to do 
assignment."

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David Scheffel

2006-Dec-28 17:20 UTC

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Re: How to hide a database column from ActiveRecord?

Chris Gernon wrote:> I believe attr_protected would be a more straightforward way to 
> accomplish this:
> 
> http://api.rubyonrails.com/classes/ActiveRecord/Base.html#M000873
> 
> "Attributes named in this macro are protected from mass-assignment,
such
> as new(attributes) and attributes=(attributes). Their assignment will 
> simply be ignored. Instead, you can use the direct writer methods to do 
> assignment."
Almost. It protects the value from being changed, but it is still 
included in the sql that is generated by ActiveRecord. Since the 
particular column is an integer[], but ActiveRecord tries to handle it 
as integer instead, it fails because of a wrong type assignment.

Maybe a better database driver would do. I''m currently using the dbi 
driver on Windows. I know there is a native one as well, but this one 
seems to be a bit tricky to install.

Looking for your suggestions
David

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Phlip

2006-Dec-28 17:30 UTC

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Re: How to hide a database column from ActiveRecord?

David Scheffel wrote:
> > Add an SQL View object and point the ActiveRecord at that.
> But could I still use that "hidden" column in a call to
find_by_sql? I
> mean since it is not part of the underlying (the view) anymore?
Sure - just write a table join between the original table and its own view.

You could even add the original table as another Model object, then
put a has_one between the two models.

-- 
  Phlip
  http://c2.com/cgi/wiki?ZeekLand  <-- NOT a blog!!

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David Scheffel

2006-Dec-28 17:41 UTC

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Re: How to hide a database column from ActiveRecord?

Phlip wrote:> David Scheffel wrote:
> 
>> > Add an SQL View object and point the ActiveRecord at that.
> 
>> But could I still use that "hidden" column in a call to
find_by_sql? I
>> mean since it is not part of the underlying (the view) anymore?
> 
> Sure - just write a table join between the original table and its own 
> view.
> 
> You could even add the original table as another Model object, then
> put a has_one between the two models.
As I''ve found out ActiveRecord can''t even handle views - at
least not
the postgres-rb driver! It tries to retrieve the structure for the view 
which obviously fails.

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kpd

2006-Dec-28 19:10 UTC

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Re: How to hide a database column from ActiveRecord?

Hi David,

I ran into a similar problem when working on BetterNestedSet-- I had
columns I wanted AR to read, but never write to.

My solution is a bit heavy-handed, but seems to work well. I overrode
the update method of Activerecord in the relevant model, so that it
won''t write that column to the database:

        private
          # call ''special_attributes_with_quotes'' method
instead of
attributes_with_quotes
          def update #:nodoc:
            connection.update(
              "UPDATE #{self.class.table_name} " +
              "SET #{quoted_comma_pair_list(connection,
special_attributes_with_quotes(false))} " +
              "WHERE #{self.class.primary_key} = #{quote_value(id)}",
              "#{self.class.name} Update"
            )
          end

          # exclude the columns from update statements
          def special_attributes_with_quotes(include_primary_key true) #:nodoc:
            attributes.inject({}) do |quoted, (name, value)|
              if column = column_for_attribute(name)
                quoted[name] = quote_value(value, column) unless
(!include_primary_key && column.primary) || [your_col_name,
your_other_col_name].include?(column.name)
              end
              quoted
            end
          end

          # i couldn''t figure out how to call attributes_with_quotes
without cutting and pasting this private method in.  :(
          # Quote strings appropriately for SQL statements.
          def quote_value(value, column = nil) #:nodoc:
            self.class.connection.quote(value, column)
          end


If you come up with a better solution please let me know!

Krishna

On Dec 28, 12:41 pm, David Scheffel
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:> Phlip wrote:
> > David Scheffel wrote:
>
> >> > Add an SQL View object and point the ActiveRecord at that.
>
> >> But could I still use that "hidden" column in a call to
find_by_sql? I
> >> mean since it is not part of the underlying (the view) anymore?
>
> > Sure - just write a table join between the original table and its own
> > view.
>
> > You could even add the original table as another Model object, then
> > put a has_one between the two models.As I''ve found out
ActiveRecord can''t even handle views - at least not
> the postgres-rb driver! It tries to retrieve the structure for the view
> which obviously fails.
> 
> --
> Posted viahttp://www.ruby-forum.com/.

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David Scheffel

2006-Dec-28 21:58 UTC

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Re: How to hide a database column from ActiveRecord?

k Thanks! You''ve made my day:-)))
> If you come up with a better solution please let me know!
I will. If I would I''ll post it here.

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kpd

2007-Jan-03 22:24 UTC

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Re: How to hide a database column from ActiveRecord?

FYI, I just found out that my solution breaks the before_update
callback (and probably others).

Krishna

On Dec 28 2006, 4:58 pm, David Scheffel
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:> k Thanks! You''ve made my day:-)))
>
> > If you come up with a better solution please let me know!I will. If I
would I''ll post it here.
> 
> --
> Posted viahttp://www.ruby-forum.com/.

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Dan Manges

2007-Jan-04 03:39 UTC

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Re: How to hide a database column from ActiveRecord?

David Scheffel wrote:> Can I tell ActiveRecord to ignore this column and not to add it to the
> Attributes array?
I submitted a patch at http://dev.rubyonrails.org/ticket/6896 which
adds an attr_readonly method to ActiveRecord::Base to ignore attributes
in update queries.  It also fixes a bug with counter_cache.  Hopefully
it receives enough support and provides enough value to be applied, but
if not I can make it into a plugin.

Dan Manges


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David Scheffel

2007-Jan-04 09:09 UTC

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Re: How to hide a database column from ActiveRecord?

Dan Manges wrote:
> I submitted a patch at http://dev.rubyonrails.org/ticket/6896 which
> adds an attr_readonly method to ActiveRecord::Base to ignore attributes
> in update queries.  
k Thanks!!

I''m really looking forward to it. How could I get notice about the next
Rails release including this patch?

Regards
//David

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Dan Manges

2007-Jan-04 16:49 UTC

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Re: How to hide a database column from ActiveRecord?

David Scheffel wrote:> I''m really looking forward to it. How could I get notice about the
next
> Rails release including this patch?
You can subscribe to the RSS feed for the patch here:
http://dev.rubyonrails.org/ticket/6896?format=rss

You may also want to leave a comment on the patch stating that you
would like to see the patch applied.  If you have time, try checking
out Rails trunk, applying the patch, and leaving a comment confirming
that the patch works.

Dan Manges


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Mark Reginald James

2007-Jan-04 18:44 UTC

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Re: How to hide a database column from ActiveRecord?

Dan Manges wrote:
> I submitted a patch at http://dev.rubyonrails.org/ticket/6896 which
> adds an attr_readonly method to ActiveRecord::Base to ignore attributes
> in update queries.  It also fixes a bug with counter_cache.  Hopefully
> it receives enough support and provides enough value to be applied, but
> if not I can make it into a plugin.
I think attr_readonly is a good solution if a different solution that
tracks and only updates changed attributes is not going to be implemented.

Something''s really needed to prevent a save writing to attributes that
are also being updated through direct database update calls (used to
most easily and properly handle concurrency).

-- 
We develop, watch us RoR, in numbers too big to ignore.


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David Scheffel

2007-Jan-11 16:47 UTC

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Re: How to hide a database column from ActiveRecord?

> You may also want to leave a comment on the patch stating that you
> would like to see the patch applied.  
I did.
> If you have time, try checking
> out Rails trunk, applying the patch, and leaving a comment confirming
> that the patch works.
How could I apply this path? I assume that it has been commited to a 
branch in svn?

Which command line would I need to call?

Thanks...
David

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Rails - Dec 2006 - How to hide a database column from ActiveRecord?

How to hide a database column from ActiveRecord?

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