Find and has_one relationships

Rails
1

I’ve got a bit stuck with using find in Ruby so was hoping for some
expert guidance as this is driving me nuts!

If I’ve got the following 2 models:

class Member < ActiveRecord::Base
has_one :site_account
end

class SiteAccount < ActiveRecord::Base
belongs_to :member
end

What this represents is a pile of members: some have site access and
some don’t

I need to get at all the members who have site access and those that
don’t and can’t work out the correct find statements to use

If I go to an individual member using

m = Member.find(1)

I can see if they have a site account by checking

m.site_account.nil? # false if they have a site account and true if
they don’t

However what I want is a list of all who don’t hgave an account and I
don’t understand why I can’t seem to refer to site_account in a find
statement to get a list of all members who don’t have a site account
without getting an error telling me that

Mysql::Error: Unknown column ‘site_account’ in ‘where clause’: SELECT *
FROM members WHERE (site_account). I’d asssumed that a clever join
statement would be constructed in the backgroud to let me do this but it
doen’t seem to. I was hoping to use something along the lines of:

m = Member.find(:all, :conditions => what_goes_in_here???)

Am I trying something that’s not possible or is it just that the syntax
is evading me? Any help hugely appreciated.

Cheers

Rupert

2

I’m not expert, but site_account is a table, not a column. And a
standard join won’t work because you’re looking for stuff that’s
not in the table. Don’t know if this will work, but perhaps
something along the lines of :conditions => “id not in (select id
from site_account)”

alternatively you might be able do it in rails with something like
Member.find(:all).delete_if { |m| !m.site_account.nil? }

Hope this of some help…

…
…
John B.

3

Article.with_scope(:find => { :conditions => "blog_id = 1 })

((taken from api.rubyonrails))

in the model of your choice, define the find method to select the
members of your choice, and walla. (you can use with_exclusive_scope if
you don’t want to ruin the find method for that model)
it would be along the lines of

Member.with_scope(:find => {:conditions => ‘site_account_id !=
nil/0/whatever-you-defined’})

or something like that.
hope it helps. check out the api docs, they are pretty self-explanitory.

harp

4

Rupert V. wrote:

I’ve got a bit stuck with using find in Ruby so was hoping for some
expert guidance as this is driving me nuts!

If I’ve got the following 2 models:

class Member < ActiveRecord::Base
has_one :site_account
end

class SiteAccount < ActiveRecord::Base
belongs_to :member
end

What this represents is a pile of members: some have site access and
some don’t

I need to get at all the members who have site access and those that
don’t and can’t work out the correct find statements to use

If I go to an individual member using

m = Member.find(1)

I can see if they have a site account by checking

m.site_account.nil? # false if they have a site account and true if
they don’t

However what I want is a list of all who don’t hgave an account and I
don’t understand why I can’t seem to refer to site_account in a find
statement to get a list of all members who don’t have a site account
without getting an error telling me that

Mysql::Error: Unknown column ‘site_account’ in ‘where clause’: SELECT *
FROM members WHERE (site_account). I’d asssumed that a clever join
statement would be constructed in the backgroud to let me do this but it
doen’t seem to. I was hoping to use something along the lines of:

m = Member.find(:all, :conditions => what_goes_in_here???)

Am I trying something that’s not possible or is it just that the syntax
is evading me? Any help hugely appreciated.

Perhaps you have the foreign key in the wrong table. You could change
things so that:

class Member < ActiveRecord::Base
belongs_to :site_account
end

class SiteAccount < ActiveRecord::Base
has_one :member
end

Then it’s easy to check member.site_account_id to see if it’s nil. The
cost is having a site_account_id field in every member row, even for
those members that don’t have a site account. And potentially it might
change how you do your joins significantly. But it’s an option to
consider.

–
Josh S.
http://blog.hasmanythrough.com

5

John B. wrote:

I’m not expert, but site_account is a table, not a column. And a
standard join won’t work because you’re looking for stuff that’s
not in the table. Don’t know if this will work, but perhaps
something along the lines of :conditions => “id not in (select id
from site_account)”

alternatively you might be able do it in rails with something like
Member.find(:all).delete_if { |m| !m.site_account.nil? }

Hope this of some help…

That worked a treat - thanks John :slight_smile:

…I tried to suss out the with_scope idea but I couldn’t get it to do
it, so you’ve saved me from having to go down Josh’s route which is wat
I reckon I would have had to have done had it not been for your
suggestion.

Thanks all!!

Rupert