This seems like it must have been asked before - I really did try to
find it in the archives, so my apologies if it’s already out there.
Utilizing ActiveRecord, I would like to specify a prefix for the
column names in my table. For example, in ‘Recipe 16 Integrating with
Legacy Databases’ (Rails Recipes, from PragProg, by Fowler) they deal
with integration with a WordPress db where all field names are
preceded by “comment_” – i.e. comment_author_email.
The recipe explains how to deal with the primary key (comment_id) via:
ActiveRecord::Base.primary_key_prefix_type = :table_name_with_underscore
which is great: the primary key would obviously be the most important
piece to get working 
However, it stops short of going into detail on dealing with this on
the other column names.
I guess what I’m looking for is a nice clean way to take their extent
their example - allowing me to reference the non-key fields as
“author_email” instead of needing to always prefix and say things like
“comment_author_email” all over my whole application. and since this
will be in a more complete environment: I also don’t want to remove
“comment_” from the front of every field name in the whole db! It
will need to be specific to the Comment class itself.
Any help is most appreciated. Thanks.
Hello Jim,
However, it stops short of going into detail on dealing with this on
the other column names.
I guess what I’m looking for is a nice clean way to take their extent
their example - allowing me to reference the non-key fields as
“author_email” instead of needing to always prefix and say things like
“comment_author_email” all over my whole application. and since this
will be in a more complete environment: I also don’t want to remove
“comment_” from the front of every field name in the whole db! It
will need to be specific to the Comment class itself.
If I understand your problem correctly, let’s say we’ve got a Author
model
with a ‘comment_author_email’ field in the associated table, and
you want to do things like :
a = Author.new
a.author_email = ‘…’
So you can use facade column ; in your model
class Author < AR::B
def author_email
read_attribute(“comment_author_email”)
end
def author_email=(email)
write_attribute(“comment_author_email”, email.to_s)
end
end
and do the same for the other fields. Maybe a sort of model scaffolding
will ease your job 
(one gotcha is the typecasting in the
write_attribute
call)
My 2 (euro)cents,
РJean-Fran̤ois.
Jean-François - Thanks for the help. Your example is just what I am
trying to do. However, I am now wondering if maybe I don’t have my
hands around exactly what is causing my issue…
For my exact application:
my field name is “user_email”, which I would like to refer to as
“email”. My table name is “common_users” and I have already taken
care of it so that I can name my class “user”.
I have the code (as you have detailed below) in my user.rb:
def email
read_attribute “user_email”
end
def email=(value)
write_attribute “user_email”, value.to_s
end
however I run into the following method and see an error when
executing save (console output below the code)
def signup
return if generate_blank
@params[‘user’].delete(‘form’)
@user = User.new(@params[‘user’])
begin
User.transaction(@user) do
@user.new_password = true
logger.warn “4444444444444444444444444444”
if @user.save
logger.warn “55555555555555555555555555555555”
#snip
end
logger.warn “66666666666666666666666666”
end
logger.warn “777777777777777777”
rescue
logger.warn “888888888888888888888”
flash.now[‘message’] = l(:user_confirmation_email_error)
end
end
###############
console output::
User Columns (0.000580) SHOW FIELDS FROM common_users
SQL (0.000113) BEGIN
4444444444444444444444444444
User Load (0.000000) Mysql::Error: Unknown column
‘common_users.email’ in ‘where clause’: SELECT * FROM common_users
WHERE (common_users.email = ‘[email protected]’) LIMIT 1
SQL (0.000109) ROLLBACK
888888888888888888888
The table name looks fine, but the field is still being referred to as
‘email’ here. I guess I’m a bit confused as to why these two
statements are running at all?
Again, thanks for the help in advance.
On 4/20/06, Jean-François [email protected] wrote:
“comment_” from the front of every field name in the whole db! It
and do the same for the other fields. Maybe a sort of model scaffolding
Rails mailing list
[email protected]
http://lists.rubyonrails.org/mailman/listinfo/rails
–
http://jimhalberg.com
I found the culprit… I had missed this guy hanging out in a cluster
of validation lines:
validates_uniqueness_of :email, :on => :create
… causing the execution of that select with the field name “email”.
Thanks a ton for the help on this Jean-François.
On 4/20/06, Jean-François [email protected] wrote:
I have the code (as you have detailed below) in my user.rb:
def signup
You can check that by unit-testing your model. Test a
…
user
–
À la renverse.
–
http://jimhalberg.com
Jim H. wrote:
ActiveRecord::Base.primary_key_prefix_type = :table_name_with_underscore
“comment_author_email” all over my whole application. and since this
will be in a more complete environment: I also don’t want to remove
“comment_” from the front of every field name in the whole db! It
will need to be specific to the Comment class itself.
Any help is most appreciated. Thanks.
I did exactly just that for my presentation at Canada on Rails…
http://rubyurl.com/DRv
-Robby
Jim :
def email
return if generate_blank
@params[‘user’].delete(‘form’)
@user = User.new(@params[‘user’])
[…]
In fact, I think there may be a problem with User#new
when passing a hash, since the constructor creates the User
instance with the help of the column definitions. As we’ve
got a facade column (let’s say faked attribute), there must be
trouble. The User#create must work correctly I think.
You can check that by unit-testing your model. Test a
User.new with a hash having a ‘email’ key.
If I’m right, it should fail. Instead,
user = User.new
user.new_password = ‘…’
user.email = ‘…’
user.save
must work (another test)
So test also User#create.
For your code, maybe a way will be :
h = params[:user]
h.remove(‘form’)
email = h[:email]
h.remove(:email)
@user = User.new(h)
@user.email = email
…
And for convenience, make it a method
class User < AR::B
maybe not a good idea to override AR::B#initialize
def self.my_special_new(hash)
email = hash[:email]
hash.remove[:email]
user = new(hash)
user.email = email
user
end
…
end
sth like that… (to be unit-tested)
Hope this helps,
РJean-Fran̤ois.
