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Franz

2008-Nov-06 04:38 UTC

active record associations

I want to accomplish the following. I have an object that can be
edited.  However, it can occur that two people might edit the object
at the same time.  Instead of locking the object down, I prefer to
tell the user how their version differs from the last version that was
committed.

Kinda like:

respond_to do |format|
  @document = Document.find_by_id(1)
  @document.attributes = params[:document]
  @changes = @document.diff(Document.find_by_id(1))
   format.html { render :action => "edit" }
end

The edit screen then renders the changes for the user to compare.  The
user can then apply some changes or ignore the changes and save.

This works fine for regular fields, but when the object has has_many
assoctiations, then the following would occur.

respond_to do |format|
  @document = Document.find_by_id(1)
  @document.attributes = params[:document]  # => this call would
update the database for all has_many associations
  @changes = @document.diff(Document.find_by_id(1))  #=> retrieving
the previous object state from the database is not possible since the
associations have changed
   format.html { render :action => "edit" }
end

I also tried to compare the object to the attributes kinda like this;

respond_to do |format|
  @document = Document.find_by_id(1)
  @changes = @document.diff(params[:document])
   format.html { render :action => "edit" }
end

But then the user''s changes aren''t stored on the object and
all
updates are lost.

Any help is appreciated.





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JL Smith

2008-Nov-06 16:54 UTC

head link

Re: active record associations

This sounds like the dirty object feature of Rails 2.1 would work
great:
http://ryandaigle.com/articles/2008/3/31/what-s-new-in-edge-rails-dirty-objects

Maybe even try to utilize some callback methods so you can capture and
display the changes to the user:
http://railsforum.com/viewtopic.php?id=23001

On Nov 5, 10:38 pm, Franz
<franz.obenhau...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> I want to accomplish the following. I have an object that can be
> edited.  However, it can occur that two people might edit the object
> at the same time.  Instead of locking the object down, I prefer to
> tell the user how their version differs from the last version that was
> committed.
>
> Kinda like:
>
> respond_to do |format|
>   @document = Document.find_by_id(1)
>   @document.attributes = params[:document]
>   @changes = @document.diff(Document.find_by_id(1))
>    format.html { render :action => "edit" }
> end
>
> The edit screen then renders the changes for the user to compare.  The
> user can then apply some changes or ignore the changes and save.
>
> This works fine for regular fields, but when the object has has_many
> assoctiations, then the following would occur.
>
> respond_to do |format|
>   @document = Document.find_by_id(1)
>   @document.attributes = params[:document]  # => this call would
> update the database for all has_many associations
>   @changes = @document.diff(Document.find_by_id(1))  #=> retrieving
> the previous object state from the database is not possible since the
> associations have changed
>    format.html { render :action => "edit" }
> end
>
> I also tried to compare the object to the attributes kinda like this;
>
> respond_to do |format|
>   @document = Document.find_by_id(1)
>   @changes = @document.diff(params[:document])
>    format.html { render :action => "edit" }
> end
>
> But then the user''s changes aren''t stored on the object
and all
> updates are lost.
>
> Any help is appreciated.--~--~---------~--~----~------------~-------~--~----~
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Franz

2008-Nov-07 03:18 UTC

head link

Re: active record associations

The dirty object feature doesn''t work for has_many associations.  I
solved the problem by wrapping a transaction around the code to revert
the changes in the database.  I kinda wish, ror could keep the
functionality between regular fields and association fields consistent
to avoid confusion.

kinda like:

class Person
  has_many :cars
end
>> person = Person.find_by_name("Jack")
>> person.cars=> [#<Car id: 2, name: "BMW", created_at: "2008-11-04
03:04:46",
updated_at: "2008-11-04 03:04:46">]>> person.cars=[Car.find_by_name("Porsche"),
Car.find_by_name("VW")]
>> person.cars=> [#<Car id: 1, name: "Porsche", created_at: "2008-11-04
03:04:46",
updated_at: "2008-11-04 03:04:46">, #<Car id: 3, name:
"VW",
created_at: "2008-11-04 03:04:46", updated_at: "2008-11-04
03:04:46">]>> person.changed?
=> true>> person.changes=> {"cars"=>[[#<Car id: 2, name: "BMW", created_at:
"2008-11-04
03:04:46", updated_at: "2008-11-04 03:04:46">], [#<Car id:
1, name:
"Porsche", created_at: "2008-11-04 03:04:46", updated_at:
"2008-11-04
03:04:46">, #<Car id: 3, name: "VW", created_at:
"2008-11-04
03:04:46", updated_at: "2008-11-04
03:04:46">]]}>> person.save  #associations are saved in the database
However ror returns the following
>> person = Person.find_by_name("Jack")
>> person.cars=> [#<Car id: 2, name: "BMW", created_at: "2008-11-04
03:04:46",
updated_at: "2008-11-04 03:04:46">]>> person.cars=[Car.find_by_name("Porsche"),
Car.find_by_name("VW")]  #associations are saved in the database
>> person.cars=> [#<Car id: 1, name: "Porsche", created_at: "2008-11-04
03:04:46",
updated_at: "2008-11-04 03:04:46">, #<Car id: 3, name:
"VW",
created_at: "2008-11-04 03:04:46", updated_at: "2008-11-04
03:04:46">]>> person.changed?
=> false>> person.changes=> {}




On Nov 7, 12:54 am, JL Smith
<autige...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> This sounds like the dirty object feature of Rails 2.1 would work
>
great:http://ryandaigle.com/articles/2008/3/31/what-s-new-in-edge-rails-dir...
>
> Maybe even try to utilize some callback methods so you can capture and
> display the changes to the
user:http://railsforum.com/viewtopic.php?id=23001
>
> On Nov 5, 10:38 pm, Franz
<franz.obenhau...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > I want to accomplish the following. I have an object that can be
> > edited.  However, it can occur that two people might edit the object
> > at the same time.  Instead of locking the object down, I prefer to
> > tell the user how their version differs from the last version that was
> > committed.
>
> > Kinda like:
>
> > respond_to do |format|
> >   @document = Document.find_by_id(1)
> >   @document.attributes = params[:document]
> >   @changes = @document.diff(Document.find_by_id(1))
> >    format.html { render :action => "edit" }
> > end
>
> > The edit screen then renders the changes for the user to compare.  The
> > user can then apply some changes or ignore the changes and save.
>
> > This works fine for regular fields, but when the object has has_many
> > assoctiations, then the following would occur.
>
> > respond_to do |format|
> >   @document = Document.find_by_id(1)
> >   @document.attributes = params[:document]  # => this call would
> > update the database for all has_many associations
> >   @changes = @document.diff(Document.find_by_id(1))  #=> retrieving
> > the previous object state from the database is not possible since the
> > associations have changed
> >    format.html { render :action => "edit" }
> > end
>
> > I also tried to compare the object to the attributes kinda like this;
>
> > respond_to do |format|
> >   @document = Document.find_by_id(1)
> >   @changes = @document.diff(params[:document])
> >    format.html { render :action => "edit" }
> > end
>
> > But then the user''s changes aren''t stored on the
object and all
> > updates are lost.
>
> > Any help is appreciated.--~--~---------~--~----~------------~-------~--~----~
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Franz

2008-Nov-07 04:17 UTC

head link

active record associations

What''s wrong with ruby associations?


Somehow association fields don''t have any support for dirty objects
nor optimistic locking.

I would expect dirty objects to work like this:

class Person
  has_many :cars
end
>> person = Person.find_by_name("Jack")
>> person.cars
=> [#<Car id: 2, name: "BMW", created_at: "2008-11-04
03:04:46",
updated_at: "2008-11-04 03:04:46">]>> person.cars=[Car.find_by_name("Porsche"),
Car.find_by_name("VW")]
>> person.cars
=> [#<Car id: 1, name: "Porsche", created_at: "2008-11-04
03:04:46",
updated_at: "2008-11-04 03:04:46">, #<Car id: 3, name:
"VW",
created_at: "2008-11-04 03:04:46", updated_at: "2008-11-04
03:04:46">]>> person.changed?
=> true>> person.changes
=> {"cars"=>[[#<Car id: 2, name: "BMW", created_at:
"2008-11-04
03:04:46", updated_at: "2008-11-04 03:04:46">], [#<Car id:
1, name:
"Porsche", created_at: "2008-11-04 03:04:46", updated_at:
"2008-11-04
03:04:46">, #<Car id: 3, name: "VW", created_at:
"2008-11-04
03:04:46", updated_at: "2008-11-04 03:04:46">]]}
>> person.save  #associations are saved in the database
However ror returns the following
>> person = Person.find_by_name("Jack")
>> person.cars
=> [#<Car id: 2, name: "BMW", created_at: "2008-11-04
03:04:46",
updated_at: "2008-11-04 03:04:46">]>> person.cars=[Car.find_by_name("Porsche"),
Car.find_by_name("VW")]  #associations are saved in the database
>> person.cars
=> [#<Car id: 1, name: "Porsche", created_at: "2008-11-04
03:04:46",
updated_at: "2008-11-04 03:04:46">, #<Car id: 3, name:
"VW",
created_at: "2008-11-04 03:04:46", updated_at: "2008-11-04
03:04:46">]>> person.changed?
=> false>> person.changes
=> {}

The same problem happens with optimistic locking

p1 = Person.find_by_name("Jack")
p2 = Person.find_by_name("Jack")

p1.cars = [Car.find_by_name("Porsche")]
p1.save

p2.cars = [Car.find_by_name("BMW")]
p2.save

I would expect the object to raise an exception, but it doesn''t.

Isn''t there a way to unify the behaviour of regular fields and
associations?  Most objects in my app don''t represent flat tables, but
tables that associate each other.  Right now I''m forced to having to
wrap many attribute updates into a transaction and write my own object
comparisons.

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