Rails - Oct 2005 - How does child know parent.id in one to many relationship?

If I have a one to many relationship, how do you relate the new child, 
to the parent?

As a practical example say I have a "projects" and "tasks"
tables. The
tasks table has a project_id field.
I generate scaffold for both.
I add "belongs_to :projects" to the Project model and "has_many
:tasks"
to the Tasks table.
So I have created the relationship.

The next thing to do is add a link on the project''s show view to create
a new task. [is this correct?]
<%= link_to ''New Task'', :controller =>
''task'', :action => ''new'' %>

This new task should be linked to the project that is being shown. This 
is where I trip up!

1.) How does the New method in task controller know what the parent id is?
2.) And secondly how does the Create method get the parent id?

1.) The new task link could include the current projects id
<%= link_to ''New Task'', :controller =>
''task'', :action => ''new'', :id =>
@project.id %>


2.) The New method could put the project id in a var which could be 
written to a hidden field (in the view) which the Create method would get.
@project_id = params[:id]


Is this correct, or is their a better way of doing this? Maybe storing 
the id in a session and having both New and Create methods read the session?
Is there an automatic, rails way, of doing this?

Thanks for any help, K.

On 9.10.2005, at 18.11, Kris Leech wrote:
> I add "belongs_to :projects" to the Project model and  
> "has_many :tasks" to the Tasks table.
Really? Because that''s backwards. Project belonging to a project and  
a task having many tasks. That''s probably not what you want. You  
should have Project "has_many :tasks" and Task "belongs_to
:project",
right?

<snip />
> 1.) The new task link could include the current projects id
> <%= link_to ''New Task'', :controller =>
''task'', :action =>
> ''new'', :id => @project.id %>
>
> 2.) The New method could put the project id in a var which could be  
> written to a hidden field (in the view) which the Create method  
> would get.
> @project_id = params[:id]
This is fine. In 2) you can do something like this:

@task = Task.new
@task.project = Project.find(params[:id]) # Or @task.project_id =  
params[:id] to avoid the db call

...and in the view:

<%= hidden_field "task", "project_id" %>

(untested code warning)

//jarkko

--
Jarkko Laine
http://jlaine.net
http://odesign.fi



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On Oct 9, 2005, at 9:06 AM, Jarkko Laine wrote:
> On 9.10.2005, at 18.11, Kris Leech wrote:
>
>> I add "belongs_to :projects" to the Project model and  
>> "has_many :tasks" to the Tasks table.
>
> Really? Because that''s backwards. Project belonging to a project  
> and a task having many tasks. That''s probably not what you want.  
> You should have Project "has_many :tasks" and Task  
> "belongs_to :project", right?
>
> <snip />
>
>> 1.) The new task link could include the current projects id
>> <%= link_to ''New Task'', :controller =>
''task'', :action =>
>> ''new'', :id => @project.id %>
>>
>> 2.) The New method could put the project id in a var which could  
>> be written to a hidden field (in the view) which the Create method  
>> would get.
>> @project_id = params[:id]
>
> This is fine. In 2) you can do something like this:
>
> @task = Task.new
> @task.project = Project.find(params[:id]) # Or @task.project_id =  
> params[:id] to avoid the db call
>
> ...and in the view:
>
> <%= hidden_field "task", "project_id" %>
Why would you store the project_id in a hidden field named task?

You could also handle the project ID via the URL:

   <%= start_form_tag { :action => ''create_seller'',
                        :id     => @project }
-- 
-- Tom Mornini

On 9.10.2005, at 20.51, Tom Mornini wrote:
> Why would you store the project_id in a hidden field named task?
>
> You could also handle the project ID via the URL:
>
>   <%= start_form_tag { :action => ''create_seller'',
>                        :id     => @project }
You''re right, you don''t need it in this case since the id of
the task
needs not to be passed (since it doesn''t even have an id yet).

//jarkko
> -- 
> -- Tom Mornini
>
> _______________________________________________
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> http://lists.rubyonrails.org/mailman/listinfo/rails
>
>
--
Jarkko Laine
http://jlaine.net
http://odesign.fi



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On 9.10.2005, at 21.14, Jarkko Laine wrote:
>
> On 9.10.2005, at 20.51, Tom Mornini wrote:
>
>> Why would you store the project_id in a hidden field named task?
Oh, btw, it''s not named task, it''s named task[project_id] so
it will
be automatically used when the task it created like this:

task = Task.new(params[:task])

Like said, it''s less typing to use the method below in this case, but  
there definitely are situations where hidden fields come in extremely  
handy.

//jarkko
>>
>> You could also handle the project ID via the URL:
>>
>>   <%= start_form_tag { :action =>
''create_seller'',
>>                        :id     => @project }
>>
--
Jarkko Laine
http://jlaine.net
http://odesign.fi



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On Oct 9, 2005, at 12:52 PM, Jarkko Laine wrote:
> On 9.10.2005, at 21.14, Jarkko Laine wrote:
>
>> On 9.10.2005, at 20.51, Tom Mornini wrote:
>>
>>> Why would you store the project_id in a hidden field named task?
>
> Oh, btw, it''s not named task, it''s named task[project_id]
so it
> will be automatically used when the task it created like this:
Oh, yes, sorry for that.

Thanks for the correction.

I''m approaching fluency, but I''m in that dangerous period
where I''m
''sure'' I understand what the natives are saying. :-)

-- 
-- Tom Mornini

>"Really? Because that''s backwards. Project belonging to a
project and
a task having many tasks. That''s probably >not what you want. You  
should have Project "has_many :tasks" and Task "belongs_to
:project",
right?"

Sorry yeah, it was a typo on my part, my code is as you describe!

@task = Task.new
@task.project_id = params[:id]

Im sure I tried this already but it did''nt work. I shall have to review
my code. But basically this should replace the need to create a seperate 
var to hold the project id that is assigned to the new task (which will 
be writtern to a hidden field in the New view)?

But... you dont need a hidden field in this case because...

Either the Create method is passed the @task var we created in the New 
action, which has the correct project id already assigned?

Or the project id is passed to the Create method as part of the form''s 
action and the code would be:

<%= start_form_tag { :action => ''create'', :id     =>
@project.id } %>

I''m I getting there? :)

On 11.10.2005, at 21.06, Kris Leech wrote:
>
> >"Really? Because that''s backwards. Project belonging to a
project
> and  a task having many tasks. That''s probably >not what you
want.
> You  should have Project "has_many :tasks" and Task  
> "belongs_to :project",  right?"
>
> Sorry yeah, it was a typo on my part, my code is as you describe!
>
> @task = Task.new
> @task.project_id = params[:id]
>
> Im sure I tried this already but it did''nt work. I shall have to  
> review my code. But basically this should replace the need to  
> create a seperate var to hold the project id that is assigned to  
> the new task (which will be writtern to a hidden field in the New  
> view)?
>
> But... you dont need a hidden field in this case because...
>
> Either the Create method is passed the @task var we created in the  
> New action, which has the correct project id already assigned?
>
> Or the project id is passed to the Create method as part of the  
> form''s action and the code would be:
>
> <%= start_form_tag { :action => ''create'', :id    
=> @project.id } %>
>
> I''m I getting there? :)
No objects are implicitly passed between actions, we''re talking about  
two separate http requests after all. The two most common ways to  
pass data in your case are either through the form (as a hidden var)  
or as part of the url. If you use the latter, you will have the  
project id at your disposal as params[:id] (in the create method)  
because you pass it as the id parameter in the form tag.

//jarkko
>
>
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
>
--
Jarkko Laine
http://jlaine.net
http://odesign.fi



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I understand the concept, but am finding the actual example hard to grasp.
If I was writing a step by step tutorial (which I will pad out for the 
wiki), it would go:

Assuming tables called Projects and Tasks, and Tasks has an int field 
called project_id

1. Create scaffold for Project and scaffold for Task
2. Add one to many relationship to models (has_many, belongs_to)
3. Go to the Project''s Show view and add a link to create a new Task, 
send project id in link.
4. Go to the Task''s New method and add ?
5. Go to the Task''s New view and add ?
6. Go to the Task''s Create method and add?

Sorry, can you spell it out for me. I know you have already helped a lot.

Many thanks, K.

Jarkko Laine wrote:
>
> On 11.10.2005, at 21.06, Kris Leech wrote:
>
>>
>> >"Really? Because that''s backwards. Project belonging
to a project
>> and  a task having many tasks. That''s probably >not what
you want.
>> You  should have Project "has_many :tasks" and Task 
"belongs_to
>> :project",  right?"
>>
>> Sorry yeah, it was a typo on my part, my code is as you describe!
>>
>> @task = Task.new
>> @task.project_id = params[:id]
>>
>> Im sure I tried this already but it did''nt work. I shall have
to
>> review my code. But basically this should replace the need to  create 
>> a seperate var to hold the project id that is assigned to  the new 
>> task (which will be writtern to a hidden field in the New  view)?
>>
>> But... you dont need a hidden field in this case because...
>>
>> Either the Create method is passed the @task var we created in the  
>> New action, which has the correct project id already assigned?
>>
>> Or the project id is passed to the Create method as part of the  
>> form''s action and the code would be:
>>
>> <%= start_form_tag { :action => ''create'', :id  
=> @project.id } %>
>>
>> I''m I getting there? :)
>
>
> No objects are implicitly passed between actions, we''re talking
about
> two separate http requests after all. The two most common ways to  
> pass data in your case are either through the form (as a hidden var)  
> or as part of the url. If you use the latter, you will have the  
> project id at your disposal as params[:id] (in the create method)  
> because you pass it as the id parameter in the form tag.
>
> //jarkko
>
>>
>>
>> _______________________________________________
>> Rails mailing list
>> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
>> http://lists.rubyonrails.org/mailman/listinfo/rails
>>
>>
>
> -- 
> Jarkko Laine
> http://jlaine.net
> http://odesign.fi
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Rails mailing list
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>http://lists.rubyonrails.org/mailman/listinfo/rails
>  
>

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fax: 0115 9663696

On 12.10.2005, at 12.30, Kris Leech wrote:
> I understand the concept, but am finding the actual example hard to  
> grasp.
> If I was writing a step by step tutorial (which I will pad out for  
> the wiki), it would go:
>
> Assuming tables called Projects and Tasks, and Tasks has an int  
> field called project_id
>
> 1. Create scaffold for Project and scaffold for Task
> 2. Add one to many relationship to models (has_many, belongs_to)
> 3. Go to the Project''s Show view and add a link to create a new  
> Task, send project id in link.
<%= link_to "Add a task", :controller => "tasks",
:action =>
"new", :id => @project %>
> 4. Go to the Task''s New method and add ?
Nothing necessarily, @params[:id] will be available to the view as such.
> 5. Go to the Task''s New view and add ?
<%= start_form_tag { :action => ''create'', :id =>
@params[:id] } %>
> 6. Go to the Task''s Create method and add?
project = Project.find(params[:id])
task = project.tasks.create(params[:task])

You can write all this in one line (Project.find(params 
[:id]).tasks.create(params[:task])) but the above might be a bit  
easier to grasp for a newbie.

Note that all the validation is omitted in the above example.

//jarkko
>
> Sorry, can you spell it out for me. I know you have already helped  
> a lot.
>
> Many thanks, K.
>
> Jarkko Laine wrote:
>
>
>>
>> On 11.10.2005, at 21.06, Kris Leech wrote:
>>
>>
>>>
>>> >"Really? Because that''s backwards. Project
belonging to a
>>> project  and  a task having many tasks. That''s probably
>not what
>>> you want.  You  should have Project "has_many :tasks" and
Task
>>> "belongs_to :project",  right?"
>>>
>>> Sorry yeah, it was a typo on my part, my code is as you describe!
>>>
>>> @task = Task.new
>>> @task.project_id = params[:id]
>>>
>>> Im sure I tried this already but it did''nt work. I shall
have to
>>> review my code. But basically this should replace the need to   
>>> create a seperate var to hold the project id that is assigned to   
>>> the new task (which will be writtern to a hidden field in the  
>>> New  view)?
>>>
>>> But... you dont need a hidden field in this case because...
>>>
>>> Either the Create method is passed the @task var we created in  
>>> the  New action, which has the correct project id already assigned?
>>>
>>> Or the project id is passed to the Create method as part of the   
>>> form''s action and the code would be:
>>>
>>> <%= start_form_tag { :action => ''create'',
:id     =>
>>> @project.id } %>
>>>
>>> I''m I getting there? :)
>>>
>>
>>
>> No objects are implicitly passed between actions, we''re
talking
>> about  two separate http requests after all. The two most common  
>> ways to  pass data in your case are either through the form (as a  
>> hidden var)  or as part of the url. If you use the latter, you  
>> will have the  project id at your disposal as params[:id] (in the  
>> create method)  because you pass it as the id parameter in the  
>> form tag.
>>
>> //jarkko
>>
>>
>>>
>>>
>>> _______________________________________________
>>> Rails mailing list
>>> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
>>> http://lists.rubyonrails.org/mailman/listinfo/rails
>>>
>>>
>>>
>>
>> -- 
>> Jarkko Laine
>> http://jlaine.net
>> http://odesign.fi
>>
>> --------------------------------------------------------------------- 
>> ---
>>
>> _______________________________________________
>> Rails mailing list
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>> http://lists.rubyonrails.org/mailman/listinfo/rails
>>
>>
>
>
> -- 
> Interkonect Services UK Ltd.
> Boundary House Main Street
> Hoveringham
> Nottingham
> NG147 JR
>
> web: www.interkonect.com
> tel: 0115 9663696
> fax: 0115 9663696
>
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
>
--
Jarkko Laine
http://jlaine.net
http://odesign.fi



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