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Alex Treber

2006-Nov-27 22:02 UTC

Newb - Active Records question

Can you sort a result set?  I''d like to have a generic query, but be
able to order it by one of the cols if a param is set.

ie
@records = Cars.find(:all, :conditions => ["color =
''Red''"], :order =>
"sales" )
@records.Orderby("Year")

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Chris Gernon

2006-Nov-27 22:32 UTC

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Re: Newb - Active Records question

Sure, a result set is really just an array of model objects, so you can 
do something like:

@records.sort_by {|record| record.year}

but why wouldn''t you just do the sort in the find? Your original code 
retrieves the records ordered by sales and then immediately discards 
that order to reorder by year. It makes more sense to just retrieve the 
records in the order you want in the first place:

if param_is_set
  @records = Cars.find(:all, :conditions => [''color = ?'',
''red''], :order
=> ''year'')
else
  @records = Cars.find(:all, :conditions => [''color = ?'',
''red''], :order
=> ''sales'')
end

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Alex Treber

2006-Nov-30 16:19 UTC

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Re: Newb - Active Records question

Thanks for the tip Chris.

The reason I wanted to know how to sort was in a few instances I need 
information that would come from the same set of data but sorted 
differently.  Just trying to skip a few trips to the DB.

If I can ask another question, how do you simplify this:

cars
id, model_id,...

models
id, description...


and if I want to have the query pull in that model description how would 
I do so?  Currenly I was using joins, but thought Active Record must 
have a better way of doing so.

@records = Car.find(:all,
   :select => " cars.*, model.description",
   :joins => " models",
   :conditions => [''color = ? AND models.id =
cars.model_id'', ''red''],
   :order => ''year'')


It works, but looks fugly.


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Chris Gernon

2006-Nov-30 17:06 UTC

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Re: Newb - Active Records question

Alex Treber wrote:> @records = Car.find(:all,
>    :select => " cars.*, model.description",
>    :joins => " models",
>    :conditions => [''color = ? AND models.id =
cars.model_id'', ''red''],
>    :order => ''year'')
> 
> 
> It works, but looks fugly.
Yep, that''s definitely more complicated than it needs to be. All you 
need to do is:

@records = Car.find(:all,
  :include => :model,
  :conditions => [''color = ?'', ''red''],
  :order => ''year'')

ActiveRecord will create the join for you. (You can also leave the 
select line as you had it, if you want to make sure no other columns 
from the models table get loaded for some reason.)

Just make sure you have belongs_to :model in your Car model and has_many 
:cars in your Model ... uh ... model. :D

Hope this helps!

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Alex Treber

2006-Nov-30 17:18 UTC

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Re: Newb - Active Records question

sweet, thanks again!

Just to ask it right away, if you have more tables would it be

 @records = Car.find(:all,
   :include => :model,
   :include => :engine,
   :conditions => [''color = ?'', ''red''],
   :order => ''year'')

or more like
 @records = Car.find(:all,
   :include => [:model, :engine],
   :conditions => [''color = ?'', ''red''],
   :order => ''year'')

or something else?
> Just make sure you have belongs_to :model in your Car model and has_many 
> :cars in your Model ... uh ... model. :D
yeah, for examples, I should pick better names sometimes. =P

Chris Gernon wrote:> Alex Treber wrote:
>> @records = Car.find(:all,
>>    :select => " cars.*, model.description",
>>    :joins => " models",
>>    :conditions => [''color = ? AND models.id =
cars.model_id'', ''red''],
>>    :order => ''year'')
>> 
>> 
>> It works, but looks fugly.
> 
> Yep, that''s definitely more complicated than it needs to be. All
you
> need to do is:
> 
> @records = Car.find(:all,
>   :include => :model,
>   :conditions => [''color = ?'',
''red''],
>   :order => ''year'')
> 
> ActiveRecord will create the join for you. (You can also leave the 
> select line as you had it, if you want to make sure no other columns 
> from the models table get loaded for some reason.)
> 
> Just make sure you have belongs_to :model in your Car model and has_many 
> :cars in your Model ... uh ... model. :D
> 
> Hope this helps!

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Alex Treber

2006-Nov-30 19:08 UTC

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Re: Newb - Active Records question

Hmm, its not quite working how I expected.

I put the has and belongs to in the model, and even after a reboot I get 
the following:
test = Cars.find(:all, :include => :make, :conditions => [...])

:I changed Model to Make, just to make things a little less murky

and when I run a debug on the screen I see:

- !ruby/object:Car
  attributes:
    model_id: 2322
    id: 3551
    date: 2006-11-03 00:00:00 -06:00
.....
  Make: &id001 !ruby/object:Make
    attributes:
      description: "BMW"
      id: 2322

- !ruby/object:Car
  attributes:
    model_id: 2322
    id: 3547
    date: 2006-11-03 00:00:00 -06:00
  Make: *id001

- !ruby/object:Car
  attributes:
    employee_id: 2457
    id: 3583
    pay_date: 2006-12-03 00:00:00 -06:00
    pay_type_id: 4
    active: 1
  Make: &id002 !ruby/object:Employee
    attributes:
      id: 2457
      description: "Buick"


Which pulls in the info, but if I try to access the data
<% test.each do |x| %>
    <%= x.description %>
<% end %>

I get
"undefined method `description'' for
#<Car:0x2afab44d08b8>"

but the following works
<% test.each do |x| %>
    <%= x.make.description %>
<% end %>

Any way to do this w/o having to write the ''make'' in there?  I
can
rewrite my code, just wondering if there is another way to do this.

Thanks

Alex

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Chris Gernon

2006-Nov-30 22:37 UTC

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Re: Newb - Active Records question

Alex Treber wrote:> but the following works
> <% test.each do |x| %>
>     <%= x.make.description %>
> <% end %>
> 
> Any way to do this w/o having to write the ''make'' in
there?  I can
> rewrite my code, just wondering if there is another way to do this.
You could probably do it by defining your own "description" method in 
your Car model, but in my opinion, you''ll be much better off in the
long
run changing your code to the way you have it above. This is the 
standard way to access columns in related tables, and sticking to it 
will make it easier for other people to read your code, and for you to 
read other people''s code.

It more accurately reflects your actual database structure: your cars 
table doesn''t have a description, but it does have a make (through the 
make_id column), and your make table has a description column. So, car 
-> make -> description ... which matches up perfectly in your ruby code 
with car.make.description. Does this make sense?

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Alex Treber

2006-Dec-01 18:07 UTC

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Re: Newb - Active Records question

Yep, that is crystal clear.  With that being the standard way of writing 
the code, I will just plan on changing things to that style.

By all means tell me to stop bugging you at any point, but heres another 
one.

I have an employees table, and another table (sales) references it.. 
twice.
so I have an employee_id, and supervisor columns, both of which are just 
employee_id numbers.

So if I wanted to write a query to get their names, how would I do it?

this would work for one column:
@records = Sale.find(:all,
  :include => :employee, #matches on employee_id column
)

but how to do the second?


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Rails - Nov 2006 - Newb - Active Records question

Newb - Active Records question

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