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Ben Teese

2008-Mar-17 03:18 UTC

Updating parent-child objects in a single transaction

Is there any way to _update_ a parent and child object in a single
transaction without having to explicitly demarcate that transaction?
I''ve got the following two objects:

class CostItem < ActiveRecord::Base
  has_one :cost :dependent => :destroy
  validates_associated :cost
end

class Cost < ActiveRecord::Base
  belongs_to :cost_item
  validates_numericality_of :amount
end

In my controller, I''ve got the following:

  def create
    @cost_item = CostItem.new(params[:cost_item])
    @cost_item.build_cost(params[:cost])
    if @cost_item.save
       ...
    else
       # Handle the error
    end
  end

  def update
    @cost_item = Item.find(params[:id])
    if @cost_item.cost.update_attributes(params[:cost]) &&
       @cost_item.update_attributes(params[:cost_item])
      ...
    else
      # Handle the error
    end
  end

The ''create'' method works transactionally - if either
@cost_item or
@cost is invalid, nothing gets saved. However, ''update'' is not
transactional: if either @cost_item or @cost is invalid, then the
valid one still gets saved.

The only way I can see around this is to put a transaction around it
and use methods that throw an exception to trigger the rollback:

 def update
    @cost_item = Item.find(params[:id])
    begin
      CostItem.transaction do
        @cost_item.cost.update_attributes!(params[:cost])
        @cost_item.update_attributes!(params[:cost_item])
        ...
      end
    rescue ActiveRecord::RecordInvalid
       # Handle the error
    end
  end

However this is a bit more verbose than I hoped. Is there any way to
make the updates of related objects fully transactional - in the same
manner as creation - without having to explicitly demarcate the
transaction?

Thanks,

Ben
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Mark Reginald James

2008-Mar-17 15:58 UTC

head link

Re: Updating parent-child objects in a single transaction

Ben Teese wrote:> Is there any way to _update_ a parent and child object in a single
> transaction without having to explicitly demarcate that transaction?
> I''ve got the following two objects:
> 
> class CostItem < ActiveRecord::Base
>   has_one :cost :dependent => :destroy
>   validates_associated :cost
> end
> 
> class Cost < ActiveRecord::Base
>   belongs_to :cost_item
>   validates_numericality_of :amount
> end
> 
> In my controller, I''ve got the following:
> 
>   def create
>     @cost_item = CostItem.new(params[:cost_item])
>     @cost_item.build_cost(params[:cost])
>     if @cost_item.save
>        ...
>     else
>        # Handle the error
>     end
>   end
> 
>   def update
>     @cost_item = Item.find(params[:id])
>     if @cost_item.cost.update_attributes(params[:cost]) &&
>        @cost_item.update_attributes(params[:cost_item])
>       ...
>     else
>       # Handle the error
>     end
>   end
def update
   @cost_item = Item.find(params[:id], :include => :cost)
   @cost_item.cost.attributes = params[:cost]
   if @cost_item.update_attributes(params[:cost_item])
     @cost_item.cost.save!
     ...
   else
     # Handle the error
   end
end

If they''re always updated together you can move the save
of cost to the model:

class CostItem
   after_update ''cost.save!''
end

You should still wrap the two saves in a transaction in
case there are DB problems, but it''s best to avoid using
transactions to recover from validation failures.

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


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coconut

2008-May-05 05:39 UTC

head link

Re: Updating parent-child objects in a single transaction

I am trying to do something very similar and i''ve got update to work,
however rails is failing on my create hierarchical xml. to use you
example, I am sending something like:

<cost_item>
  <name>blah</name>
  <description>blah</description>
  <cost>
    <amount>10</amount>
  </cost>
</cost_item>

what xml format do you post to get this to work?

On Mar 16, 8:18 pm, Ben Teese
<ben.te...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> Is there any way to _update_ a parent and child object in
asingletransactionwithout having to explicitly demarcate thattransaction?
> I''ve got the following twoobjects:
>
> class CostItem < ActiveRecord::Base
>   has_one :cost :dependent => :destroy
>   validates_associated :cost
> end
>
> class Cost < ActiveRecord::Base
>   belongs_to :cost_item
>   validates_numericality_of :amount
> end
>
> In my controller, I''ve got the following:
>
>   def create
>     @cost_item = CostItem.new(params[:cost_item])
>     @cost_item.build_cost(params[:cost])
>     if @cost_item.save
>        ...
>     else
>        # Handle the error
>     end
>   end
>
>   def update
>     @cost_item = Item.find(params[:id])
>     if @cost_item.cost.update_attributes(params[:cost]) &&
>        @cost_item.update_attributes(params[:cost_item])
>       ...
>     else
>       # Handle the error
>     end
>   end
>
> The ''create'' method works transactionally - if either
@cost_item or
> @cost is invalid, nothing gets saved. However, ''update''
is not
> transactional: if either @cost_item or @cost is invalid, then the
> valid one still gets saved.
>
> The only way I can see around this is to put atransactionaround it
> and use methods that throw an exception to trigger the rollback:
>
>  def update
>     @cost_item = Item.find(params[:id])
>     begin
>       CostItem.transactiondo
>         @cost_item.cost.update_attributes!(params[:cost])
>         @cost_item.update_attributes!(params[:cost_item])
>         ...
>       end
>     rescue ActiveRecord::RecordInvalid
>        # Handle the error
>     end
>   end
>
> However this is a bit more verbose than I hoped. Is there any way to
> make the updates of relatedobjectsfully transactional - in the same
> manner as creation - without having to explicitly demarcate thetransaction?
>
> Thanks,
>
> Ben
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Frederick Cheung

2008-May-05 09:34 UTC

head link

Re: Updating parent-child objects in a single transaction

On 17 Mar 2008, at 15:58, Mark Reginald James wrote:>
> If they''re always updated together you can move the save
> of cost to the model:
>
> class CostItem
>   after_update ''cost.save!''
> end
>
> You should still wrap the two saves in a transaction in
> case there are DB problems, but it''s best to avoid using
> transactions to recover from validation failures.
before_save, the actual save and after_save are wrapped in a  
transaction for you.

Fred

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Ben Teese

2008-May-05 23:48 UTC

head link

Re: Updating parent-child objects in a single transaction

I''m just using a HTTP POST with parameters, not XML. I''m not
sure how it''d
work with XML.

Cheers,

Ben

On Mon, May 5, 2008 at 3:39 PM, coconut
<Tomer.Doron-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> I am trying to do something very similar and i''ve got update to
work,
> however rails is failing on my create hierarchical xml. to use you
> example, I am sending something like:
>
> <cost_item>
>  <name>blah</name>
>  <description>blah</description>
>  <cost>
>    <amount>10</amount>
>  </cost>
> </cost_item>
>
> what xml format do you post to get this to work?
>
> On Mar 16, 8:18 pm, Ben Teese
<ben.te...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > Is there any way to _update_ a parent and child object in
> asingletransactionwithout having to explicitly demarcate thattransaction?
> > I''ve got the following twoobjects:
> >
> > class CostItem < ActiveRecord::Base
> >   has_one :cost :dependent => :destroy
> >   validates_associated :cost
> > end
> >
> > class Cost < ActiveRecord::Base
> >   belongs_to :cost_item
> >   validates_numericality_of :amount
> > end
> >
> > In my controller, I''ve got the following:
> >
> >   def create
> >     @cost_item = CostItem.new(params[:cost_item])
> >     @cost_item.build_cost(params[:cost])
> >     if @cost_item.save
> >        ...
> >     else
> >        # Handle the error
> >     end
> >   end
> >
> >   def update
> >     @cost_item = Item.find(params[:id])
> >     if @cost_item.cost.update_attributes(params[:cost]) &&
> >        @cost_item.update_attributes(params[:cost_item])
> >       ...
> >     else
> >       # Handle the error
> >     end
> >   end
> >
> > The ''create'' method works transactionally - if
either @cost_item or
> > @cost is invalid, nothing gets saved. However,
''update'' is not
> > transactional: if either @cost_item or @cost is invalid, then the
> > valid one still gets saved.
> >
> > The only way I can see around this is to put atransactionaround it
> > and use methods that throw an exception to trigger the rollback:
> >
> >  def update
> >     @cost_item = Item.find(params[:id])
> >     begin
> >       CostItem.transactiondo
> >         @cost_item.cost.update_attributes!(params[:cost])
> >         @cost_item.update_attributes!(params[:cost_item])
> >         ...
> >       end
> >     rescue ActiveRecord::RecordInvalid
> >        # Handle the error
> >     end
> >   end
> >
> > However this is a bit more verbose than I hoped. Is there any way to
> > make the updates of relatedobjectsfully transactional - in the same
> > manner as creation - without having to explicitly demarcate
> thetransaction?
> >
> > Thanks,
> >
> > Ben
>
> >
>

-- 
iZepto: Timesheets Made Human
http://izepto.com

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Rails - Mar 2008 - Updating parent-child objects in a single transaction

Updating parent-child objects in a single transaction

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