Rails - Aug 2012 - Ensure that only one member of a collection has the "current" flag set

I have a model that includes a :current boolean. The idea is that there are many
home pages that the admin is working on at any given time, but only one is
current at a time. At the moment, I have enforced this with the following:

before_save :toggle_current

  def toggle_current
    if current?
      Home.where(["current = ? & id != ?", true, self.id]).each do
|home|
        home.update_attribute(:current, false)
      end
    end
  end

Which works, but feels like a heavy solution to a simple problem. I could add a
set of radio buttons to the index view and set it that way, but does anyone else
have any other suggestions?

Thanks in advance,

Walter

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On 29 August 2012 16:13, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org>
wrote:
> I have a model that includes a :current boolean. The idea is that there are
many home pages that the admin is working on at any given time, but only one is
current at a time. At the moment, I have enforced this with the following:
>
> before_save :toggle_current
>
>   def toggle_current
>     if current?
>       Home.where(["current = ? & id != ?", true,
self.id]).each do |home|
>         home.update_attribute(:current, false)
>       end
>     end
>   end
you could use "update_all" rather than iterate a collection, which
would only fire one SQL query.

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NICE! Arel collapsed the getting and setting to a single query: UPDATE
"homes" SET "current" = ''f'' WHERE (current
= ''t'' & id != 3).
On Aug 29, 2012, at 11:21 AM, Michael Pavling wrote:
> On 29 August 2012 16:13, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org> wrote:
>> I have a model that includes a :current boolean. The idea is that there
are many home pages that the admin is working on at any given time, but only one
is current at a time. At the moment, I have enforced this with the following:
>> 
>> before_save :toggle_current
>> 
>>  def toggle_current
>>    if current?
>>      Home.where(["current = ? & id != ?", true,
self.id]).each do |home|
>>        home.update_attribute(:current, false)
>>      end
>>    end
>>  end
> 
> you could use "update_all" rather than iterate a collection,
which
> would only fire one SQL query.
NICE! Arel collapsed the getting and setting to a single query: UPDATE
"homes" SET "current" = ''f'' WHERE (current
= ''t'' & id != 3).

Thanks for the suggestion!

Walter

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On 29 August 2012 16:13, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org>
wrote:
> I have a model that includes a :current boolean. The idea is that there are
many home pages that the admin is working on at any given time, but only one is
current at a time. At the moment, I have enforced this with the following:
I think you may have this the wrong way round, instead of remembering
which one is current in the page put it in the admin model, then you
only need to change it there and not touch the pages at all.

Colin

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On Aug 29, 2012, at 12:04 PM, Colin Law wrote:
> On 29 August 2012 16:13, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org> wrote:
>> I have a model that includes a :current boolean. The idea is that there
are many home pages that the admin is working on at any given time, but only one
is current at a time. At the moment, I have enforced this with the following:
> 
> I think you may have this the wrong way round, instead of remembering
> which one is current in the page put it in the admin model, then you
> only need to change it there and not touch the pages at all.
Admin is a subset of User, I was referring to him or her as a person, not a
model. I am not sure why that model would be the place, though. I want to route
/home to homes#default, where homes_controller#default looks like this:

  def default
    @home = Home.default
    render :action => ''show''
  end

and home#default looks like this:

  def self.default
    @default ||= Home.where(:current => true).first ||
Home.order(''added_at DESC'').first || Home.new
  end

This is all working, I was just looking for a way to make it more canonical.

Walter
> 
> Colin
> 
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> 
> 
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On 29 August 2012 18:44, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org>
wrote:
>
> On Aug 29, 2012, at 12:04 PM, Colin Law wrote:
>
>> On 29 August 2012 16:13, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org> wrote:
>>> I have a model that includes a :current boolean. The idea is that
there are many home pages that the admin is working on at any given time, but
only one is current at a time. At the moment, I have enforced this with the
following:
>>
>> I think you may have this the wrong way round, instead of remembering
>> which one is current in the page put it in the admin model, then you
>> only need to change it there and not touch the pages at all.
>
> Admin is a subset of User, I was referring to him or her as a person, not a
model. I am not sure why that model would be the place, though. I want to route
/home to homes#default, where homes_controller#default looks like this:
Database design is nothing to do with routing.  Get the database
design right and separately sort out what views you want and hence the
controllers and routing.  You said that an admin (that is a User) at
any time has one current home page.  You have gone for the solution of
remembering in the page record that it is, or is not, current, which
involves the problems you have found with making sure that only one is
current at any one time.  Also there is redundant information in the
db, the fact that one of the records has its current flag set implies
that all the others are clear.  In addition it is possible to have an
illegal condition in the database where more than one is marked as
current, these both suggest that there may be a better way of
organising the data.  An alternative solution is to remember in the
User record which page is his current home page, which appears to me
be an easier solution and is much less prone to subtle programming
errors.

Colin

>
>   def default
>     @home = Home.default
>     render :action => ''show''
>   end
>
> and home#default looks like this:
>
>   def self.default
>     @default ||= Home.where(:current => true).first ||
Home.order(''added_at DESC'').first || Home.new
>   end
>
> This is all working, I was just looking for a way to make it more
canonical.
>
> Walter
>
>>
>> Colin
>>
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>>
>>
>
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On Aug 29, 2012, at 3:56 PM, Colin Law wrote:
> On 29 August 2012 18:44, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org> wrote:
>> 
>> On Aug 29, 2012, at 12:04 PM, Colin Law wrote:
>> 
>>> On 29 August 2012 16:13, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org> wrote:
>>>> I have a model that includes a :current boolean. The idea is
that there are many home pages that the admin is working on at any given time,
but only one is current at a time. At the moment, I have enforced this with the
following:
>>> 
>>> I think you may have this the wrong way round, instead of
remembering
>>> which one is current in the page put it in the admin model, then
you
>>> only need to change it there and not touch the pages at all.
>> 
>> Admin is a subset of User, I was referring to him or her as a person,
not a model. I am not sure why that model would be the place, though. I want to
route /home to homes#default, where homes_controller#default looks like this:
> 
> Database design is nothing to do with routing.  Get the database
> design right and separately sort out what views you want and hence the
> controllers and routing.  You said that an admin (that is a User) at
> any time has one current home page.  You have gone for the solution of
> remembering in the page record that it is, or is not, current, which
> involves the problems you have found with making sure that only one is
> current at any one time.  Also there is redundant information in the
> db, the fact that one of the records has its current flag set implies
> that all the others are clear.  In addition it is possible to have an
> illegal condition in the database where more than one is marked as
> current, these both suggest that there may be a better way of
> organising the data.  An alternative solution is to remember in the
> User record which page is his current home page, which appears to me
> be an easier solution and is much less prone to subtle programming
> errors.
Oh, I see what you were thinking. This is not the Admin''s (personal)
home page, it is the one and only home page for the entire public site. The
admin is responsible for assembling this home page by choosing items to featured
on it, but the home page that results (one of many that the admin may be working
on for future use) is going to be shown to the world one at a time, by means of
the current flag.

Does that change your mind about what I might want to do here?

Walter
> 
> Colin
> 
> 
>> 
>>  def default
>>    @home = Home.default
>>    render :action => ''show''
>>  end
>> 
>> and home#default looks like this:
>> 
>>  def self.default
>>    @default ||= Home.where(:current => true).first ||
Home.order(''added_at DESC'').first || Home.new
>>  end
>> 
>> This is all working, I was just looking for a way to make it more
canonical.
>> 
>> Walter
>> 
>>> 
>>> Colin
>>> 
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>>> 
>> 
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>> 
> 
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On 29 August 2012 21:17, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org>
wrote:
>
> On Aug 29, 2012, at 3:56 PM, Colin Law wrote:
>
>> On 29 August 2012 18:44, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org> wrote:
>>>
>>> On Aug 29, 2012, at 12:04 PM, Colin Law wrote:
>>>
>>>> On 29 August 2012 16:13, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org> wrote:
>>>>> I have a model that includes a :current boolean. The idea
is that there are many home pages that the admin is working on at any given
time, but only one is current at a time. At the moment, I have enforced this
with the following:
>>>>
>>>> I think you may have this the wrong way round, instead of
remembering
>>>> which one is current in the page put it in the admin model,
then you
>>>> only need to change it there and not touch the pages at all.
>>>
>>> Admin is a subset of User, I was referring to him or her as a
person, not a model. I am not sure why that model would be the place, though. I
want to route /home to homes#default, where homes_controller#default looks like
this:
>>
>> Database design is nothing to do with routing.  Get the database
>> design right and separately sort out what views you want and hence the
>> controllers and routing.  You said that an admin (that is a User) at
>> any time has one current home page.  You have gone for the solution of
>> remembering in the page record that it is, or is not, current, which
>> involves the problems you have found with making sure that only one is
>> current at any one time.  Also there is redundant information in the
>> db, the fact that one of the records has its current flag set implies
>> that all the others are clear.  In addition it is possible to have an
>> illegal condition in the database where more than one is marked as
>> current, these both suggest that there may be a better way of
>> organising the data.  An alternative solution is to remember in the
>> User record which page is his current home page, which appears to me
>> be an easier solution and is much less prone to subtle programming
>> errors.
>
> Oh, I see what you were thinking. This is not the Admin''s
(personal) home page, it is the one and only home page for the entire public
site. The admin is responsible for assembling this home page by choosing items
to featured on it, but the home page that results (one of many that the admin
may be working on for future use) is going to be shown to the world one at a
time, by means of the current flag.
>
> Does that change your mind about what I might want to do here?
Yes, obviously, it can''t go in the User record.  I still would not put
it in the page however, if necessary put it in a separate table with a
single record with a single field (though I suspect you might find
other stuff to put there).  The code will be simpler.  You would not
have had to ask here how to do it for example.  It is nearly always
best to use the simplest possible solution.  Also the automated tests
will be much simpler.

Colin
>
> Walter
>
>>
>> Colin
>>
>>
>>>
>>>  def default
>>>    @home = Home.default
>>>    render :action => ''show''
>>>  end
>>>
>>> and home#default looks like this:
>>>
>>>  def self.default
>>>    @default ||= Home.where(:current => true).first ||
Home.order(''added_at DESC'').first || Home.new
>>>  end
>>>
>>> This is all working, I was just looking for a way to make it more
canonical.
>>>
>>> Walter
>>>
>>>>
>>>> Colin
>>>>
>>>> --
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>>>>
>>>>
>>>
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>>>
>>
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>>
>
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