Rails - Jun 2005 - New records for models with calculated fields...

I have this structure:

create table party (
id int autonum not null primary key,
type varchar(50),
name varchar(50),
firstname varchar(50),
lastname varchar(50)
)

app\models\party.rb:
class Party << ActiveRecord::Base
...
end

app\models\person.rb
class Person < Party      ''type = Person
  def name ''fill in the empty "name" field
      read_attribute("firstname") + " " +
read_attribute("lastname")
  end
end

...and I''ve generated my views via ruby script\generate scaffold
person.

listing, showing and editing existing Persons, the calculated field
works just dandy.
but I''m getting an error when trying to create a new Person:

-----
 Showing /people/_form.rhtml where line #5 raised:

undefined method `+'' for nil:NilClass

Extracted source (around line #5):

2: 
3: <!--[form:person]-->
4: <p><label for="person_name">Name</label>
5: <%= content_tag "br", @person.name %>
6: 
7: <p><label
for="person_firstname">Firstname</label><br/>
8: <%= text_field ''person'', ''firstname'' 
%></p>

I imagine I have to do some kungfu (i.e., something like 
  <%= content_tag "br", @person.exists? @person.name :
"") %>
What is really the correct syntax?

Also, is there any way to force a given column (i.e., named
''type'') to
not be classified as a "system'' column when using
Object.content_columns? I tried overriding the method in the model,
but that didn''t seem to really help.

On Jun 22, 2005, at 7:22 PM, Corey Lawson wrote:
> I have this structure:
>
> create table party (
> id int autonum not null primary key,
> type varchar(50),
> name varchar(50),
> firstname varchar(50),
> lastname varchar(50)
> )
>
> app\models\party.rb:
> class Party << ActiveRecord::Base
> ...
> end
>
I don''t see it explicitly (perhaps in the <snipped> part of your
class?) but the table name is usually pluralized (create table  
parties) so that the model can autodetect the name (Part).
> app\models\person.rb
> class Person < Party      ''type = Person
>   def name ''fill in the empty "name" field
>       read_attribute("firstname") + " " +
read_attribute("lastname")
>   end
> end
>
You can do this inside your model:
def name ''fill in the empty "name" field
   read_attribute("firstname") + " " +
read_attribute("lastname")
rescue nil
end
> 3: <!--[form:person]-->
> 4: <p><label for="person_name">Name</label>
> 5: <%= content_tag "br", @person.name %>
> 6:
> 7: <p><label
for="person_firstname">Firstname</label><br/>
> 8: <%= text_field ''person'',
''firstname''  %></p>
>
> I imagine I have to do some kungfu (i.e., something like
>   <%= content_tag "br", @person.exists? @person.name :
"") %>
> What is really the correct syntax?
If you add the "rescue nil" to your model, then in your views you can
do this:
   <%= content_tag "br", (@person.name || "[none]") %>

Alternatively, if you want to handle the exception in your view, (in  
this case not placing the rescue in the model), you could do this:
   <%= content_tag "br", (@person.name rescue "[none]")
%>
> Also, is there any way to force a given column (i.e., named
''type'') to
> not be classified as a "system'' column when using
> Object.content_columns? I tried overriding the method in the model,
> but that didn''t seem to really help.
You can either override the content_columns method in  
ActiveRecord::Base (not recommended) or you can do this in your model:

class Person < Party
     set_inheritance_column "field"
end

Where "field" is something other than "type" (I
don''t think it has to
actually be a valid field name, and you might possibly be able to set  
it to "" or nil).

Duane Johnson
(canadaduane)




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