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Justin Copeland

2006-Jul-14 06:29 UTC

[Rails] compare two tables and find the difference?

I need to compare a column in TableA to a column in TableB and then 
select 3 columns from TableA for all the records in TableA that don''t 
exist in TableB.

TableA and TableB are different but do have one field in common that i 
am comparing. The tables are not related in anyway.

right now I have a find_by_sql query located in a model that looks like 
this:
  def self.absent_charges
    find_by_sql <<-QUERY
      SELECT sources.charge_id_number, sources.charge_name, 
sources.offense_level
        FROM sources
          LEFT JOIN charges ON sources.charge_id_number = 
charges.charge_id_number
        WHERE charges.id IS NULL
    QUERY
  end

I also need to dedupe what ends up in my final collection after the 
find_by_sql query, but I am not sure how to go about this. Is there a 
better way to do this? Any suggestions?

My view takes the 3 columns from the TableA records and presents them 
for editing before they are added to TableB.

The update_charges.rhtml view:
<h2>Add missing records to charges table</h2>
<%= start_form_tag %>
<table>
  <th>Charge id number</th>
  <th>Charge name</th>
  <th>Classification level</th>
  <%= render :partial => ''charge'', :collection =>
@new_charges %>
</table>
<%= submit_tag ''Save'' %>
<%= end_form_tag %>

the partial _charge.rhtml:
<tr>
  <td><%= hidden_field_tag 
"charge[#{charge_counter}][charge_id_number]", charge.charge_id_number
%><%= charge.charge_id_number %></td>
  <td><%= text_field_tag "charge[#{charge_counter}][name]", 
charge.charge_name, :size => 50 %></td>
  <td><%= collection_select ''charge'',
''charge_type_id'', @charge_types,
''id'', ''full_name'' %></td>
</tr>

the relevant part of the controller:
class ImportController < ApplicationController
...

  def update_charges

    @new_charges = Source.absent_charges
    @charge_types = ChargeType.find(:all)

    if request.get?
      redirect_to :action => ''update_tables'' if
@new_charges.empty?
    else
      begin
        params[:charge].each do |key, row|
          Charge.create!(row)
        end
      rescue Exception => e
        flash[:notice] = "Can''t update charges table: " + e
        redirect_to :action => ''update_tables''
      else
        flash[:notice] = ''Charges table was succesfully
updated.''
        redirect_to :action => ''update_tables''
      end
    end
  end

...
end

it is late, i am tired, and i am having a hard time even explaining what 
needs to be done. i hope someone can help me get this on track. right 
now i can get it to select the correct items, but there are duplicates 
which i don''t want, and if i perform the update_charges twice in a row 
the find_by_sql appends the same data and presents it twice in my view. 
i guess i need to initialize the absent_charges somehow? any help 
greatly appreciated.

-- 
Posted via http://www.ruby-forum.com/.

Dan Kohn

2006-Jul-14 07:09 UTC

head link

[Rails] compare two tables and find the difference?

You can get the SQL query to remove duplicates by using DISTINCT:

SELECT DISTINCT sources.charge_id_number, sources.charge_name...

Why don''t you try that and then report back what bugs you''re
still
seeing.

Separately, you don''t seem to be using Rails idiomatic column names,  
which are very helpful for setting up associations.  Essentially, you  
would replace charge_id_number with charge_id (if you''re not already  
using charge_id).  I would expect to see "LEFT JOIN charges ON  
sources.charge_id = charges.id".

            - dan
-- 
Dan Kohn <mailto:dan@dankohn.com>
<http://www.dankohn.com/>  <tel:+1-415-233-1000>



On Jul 13, 2006, at 11:28 PM, Justin Copeland wrote:
> I need to compare a column in TableA to a column in TableB and then
> select 3 columns from TableA for all the records in TableA that
don''t
> exist in TableB.
>
> TableA and TableB are different but do have one field in common that i
> am comparing. The tables are not related in anyway.
>
> right now I have a find_by_sql query located in a model that looks  
> like
> this:
>   def self.absent_charges
>     find_by_sql <<-QUERY
>       SELECT sources.charge_id_number, sources.charge_name,
> sources.offense_level
>         FROM sources
>           LEFT JOIN charges ON sources.charge_id_number >
charges.charge_id_number
>         WHERE charges.id IS NULL
>     QUERY
>   end
>
> I also need to dedupe what ends up in my final collection after the
> find_by_sql query, but I am not sure how to go about this. Is there a
> better way to do this? Any suggestions?
>
> My view takes the 3 columns from the TableA records and presents them
> for editing before they are added to TableB.
>
> The update_charges.rhtml view:
> <h2>Add missing records to charges table</h2>
> <%= start_form_tag %>
> <table>
>   <th>Charge id number</th>
>   <th>Charge name</th>
>   <th>Classification level</th>
>   <%= render :partial => ''charge'', :collection
=> @new_charges %>
> </table>
> <%= submit_tag ''Save'' %>
> <%= end_form_tag %>
>
> the partial _charge.rhtml:
> <tr>
>   <td><%= hidden_field_tag
> "charge[#{charge_counter}][charge_id_number]",
charge.charge_id_number
> %><%= charge.charge_id_number %></td>
>   <td><%= text_field_tag
"charge[#{charge_counter}][name]",
> charge.charge_name, :size => 50 %></td>
>   <td><%= collection_select ''charge'',
''charge_type_id'', @charge_types,
> ''id'', ''full_name'' %></td>
> </tr>
>
> the relevant part of the controller:
> class ImportController < ApplicationController
> ...
>
>   def update_charges
>
>     @new_charges = Source.absent_charges
>     @charge_types = ChargeType.find(:all)
>
>     if request.get?
>       redirect_to :action => ''update_tables'' if
@new_charges.empty?
>     else
>       begin
>         params[:charge].each do |key, row|
>           Charge.create!(row)
>         end
>       rescue Exception => e
>         flash[:notice] = "Can''t update charges table: "
+ e
>         redirect_to :action => ''update_tables''
>       else
>         flash[:notice] = ''Charges table was succesfully
updated.''
>         redirect_to :action => ''update_tables''
>       end
>     end
>   end
>
> ...
> end
>
> it is late, i am tired, and i am having a hard time even explaining  
> what
> needs to be done. i hope someone can help me get this on track. right
> now i can get it to select the correct items, but there are duplicates
> which i don''t want, and if i perform the update_charges twice in a
row
> the find_by_sql appends the same data and presents it twice in my  
> view.
> i guess i need to initialize the absent_charges somehow? any help
> greatly appreciated.
>
> -- 
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails

Dan Kohn

2006-Jul-14 07:46 UTC

head link

[Rails] compare two tables and find the difference?

Note that if you use idiomatic column names, I believe you may be  
able to do the search without even needing find_by_sql (not that you  
should be ashamed to drop into SQL now and then for challenging  
queries).  I think you can lose the model method and just use  
something like this in the controller:

@new_charges = Source.find( :all, :include => :charges, :select =>  
"DISTINCT id, charge_name, offense_level", :conditions =>  
["charges.id = ?", nil])

However, this may not work because eager loading supports conditions  
on the first table but not joined ones.  See eager loading here:   
http://api.rubyonrails.com/classes/ActiveRecord/Associations/ 
ClassMethods.html

            - dan
-- 
Dan Kohn <mailto:dan@dankohn.com>
<http://www.dankohn.com/>  <tel:+1-415-233-1000>



On Jul 14, 2006, at 12:09 AM, Dan Kohn wrote:
> You can get the SQL query to remove duplicates by using DISTINCT:
>
> SELECT DISTINCT sources.charge_id_number, sources.charge_name...
>
> Why don''t you try that and then report back what bugs
you''re still
> seeing.
>
> Separately, you don''t seem to be using Rails idiomatic column  
> names, which are very helpful for setting up associations.   
> Essentially, you would replace charge_id_number with charge_id (if  
> you''re not already using charge_id).  I would expect to see
"LEFT
> JOIN charges ON sources.charge_id = charges.id".
>
>            - dan
> -- 
> Dan Kohn <mailto:dan@dankohn.com>
> <http://www.dankohn.com/>  <tel:+1-415-233-1000>
>
>
>
> On Jul 13, 2006, at 11:28 PM, Justin Copeland wrote:
>
>> I need to compare a column in TableA to a column in TableB and then
>> select 3 columns from TableA for all the records in TableA that
don''t
>> exist in TableB.
>>
>> TableA and TableB are different but do have one field in common  
>> that i
>> am comparing. The tables are not related in anyway.
>>
>> right now I have a find_by_sql query located in a model that looks  
>> like
>> this:
>>   def self.absent_charges
>>     find_by_sql <<-QUERY
>>       SELECT sources.charge_id_number, sources.charge_name,
>> sources.offense_level
>>         FROM sources
>>           LEFT JOIN charges ON sources.charge_id_number >>
charges.charge_id_number
>>         WHERE charges.id IS NULL
>>     QUERY
>>   end
>>
>> I also need to dedupe what ends up in my final collection after the
>> find_by_sql query, but I am not sure how to go about this. Is there a
>> better way to do this? Any suggestions?
>>
>> My view takes the 3 columns from the TableA records and presents them
>> for editing before they are added to TableB.
>>
>> The update_charges.rhtml view:
>> <h2>Add missing records to charges table</h2>
>> <%= start_form_tag %>
>> <table>
>>   <th>Charge id number</th>
>>   <th>Charge name</th>
>>   <th>Classification level</th>
>>   <%= render :partial => ''charge'', :collection
=> @new_charges %>
>> </table>
>> <%= submit_tag ''Save'' %>
>> <%= end_form_tag %>
>>
>> the partial _charge.rhtml:
>> <tr>
>>   <td><%= hidden_field_tag
>> "charge[#{charge_counter}][charge_id_number]",  
>> charge.charge_id_number
>> %><%= charge.charge_id_number %></td>
>>   <td><%= text_field_tag
"charge[#{charge_counter}][name]",
>> charge.charge_name, :size => 50 %></td>
>>   <td><%= collection_select ''charge'',
''charge_type_id'',
>> @charge_types,
>> ''id'', ''full_name'' %></td>
>> </tr>
>>
>> the relevant part of the controller:
>> class ImportController < ApplicationController
>> ...
>>
>>   def update_charges
>>
>>     @new_charges = Source.absent_charges
>>     @charge_types = ChargeType.find(:all)
>>
>>     if request.get?
>>       redirect_to :action => ''update_tables'' if
@new_charges.empty?
>>     else
>>       begin
>>         params[:charge].each do |key, row|
>>           Charge.create!(row)
>>         end
>>       rescue Exception => e
>>         flash[:notice] = "Can''t update charges table:
" + e
>>         redirect_to :action => ''update_tables''
>>       else
>>         flash[:notice] = ''Charges table was succesfully
updated.''
>>         redirect_to :action => ''update_tables''
>>       end
>>     end
>>   end
>>
>> ...
>> end
>>
>> it is late, i am tired, and i am having a hard time even  
>> explaining what
>> needs to be done. i hope someone can help me get this on track. right
>> now i can get it to select the correct items, but there are  
>> duplicates
>> which i don''t want, and if i perform the update_charges twice
in a
>> row
>> the find_by_sql appends the same data and presents it twice in my  
>> view.
>> i guess i need to initialize the absent_charges somehow? any help
>> greatly appreciated.
>>
>> -- 
>> Posted via http://www.ruby-forum.com/.
>> _______________________________________________
>> Rails mailing list
>> Rails@lists.rubyonrails.org
>> http://lists.rubyonrails.org/mailman/listinfo/rails
>

Justin Copeland

2006-Jul-14 15:20 UTC

head link

[Rails] Re: compare two tables and find the difference?

The use of DISTINCT seemed to fix my problem. Thanks!

Dan Kohn wrote:> You can get the SQL query to remove duplicates by using DISTINCT:
> 
> SELECT DISTINCT sources.charge_id_number, sources.charge_name...
> 
> Why don''t you try that and then report back what bugs
you''re still
> seeing.
> 
> Separately, you don''t seem to be using Rails idiomatic column
names,
> which are very helpful for setting up associations.  Essentially, you
> would replace charge_id_number with charge_id (if you''re not
already
> using charge_id).  I would expect to see "LEFT JOIN charges ON
> sources.charge_id = charges.id".
> 
>             - dan
> --
> Dan Kohn <mailto:dan@dankohn.com>
> <http://www.dankohn.com/>  <tel:+1-415-233-1000>

-- 
Posted via http://www.ruby-forum.com/.

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