Why does ActiveRecord allow perception of success when updating an ID, however it doesn't really wor

greg · January 11, 2009, 11:09am

Hi,
Why does ActiveRecord allow perception of success when updating an ID,
however it doesn’t really work(i.e. no change in database)?

Here’s an example. The update of “id” versus update of a non-existent
attribute.

?> ai = AccountItem.find(:first) => #<AccountItem id: 1, account_id: 1,
date: “2009-01-11”, amount: #BigDecimal:22fb334,‘0.1E2’,4(8), balance:
#BigDecimal:22fb1f4,‘0.0’,4(8), description: “test”, notes: nil,
created_at: “2009-01-11 09:47:28”, updated_at: “2009-01-11 09:47:28”> >>
ai.update_attributes!(:id => 99999) => true # SEEMS TO INDICATE IT
WORKED >>
AccountItem.find(:all) => [#<AccountItem id: 1, account_id: 1, date:
“2009-01-11”, amount: #BigDecimal:22f27c0,‘0.1E2’,4(8), balance:
#BigDecimal:22f2680,‘0.0’,4(8), description: “test”, notes: nil,
created_at: “2009-01-11 09:47:28”, updated_at: “2009-01-11 09:47:28”>] #
IT
DIDN’T AS THE ID IS STILL 1 >>
?> ai.update_attributes!(:XXXX => 99999) NoMethodError: undefined method
XXXX=' for #<AccountItem:0x22fc6a8> <== THIS IS A BIT MORE LIKE YOU WOULD EXPECT from /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.1.1/lib/active_record/attribute_methods.rb:251:inmethod_missing’ from
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.1.1/lib/active_record/base.rb:2372:in
send' from /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.1.1/lib/active_record/base.rb:2372:inattributes=’ from
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.1.1/lib/active_record/base.rb:2371:in
each' from /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.1.1/lib/active_record/base.rb:2371:inattributes=’ from
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.1.1/lib/active_record/base.rb:2278:in
`update_attributes!’ from (irb):60 >>

thanks

greg · January 11, 2009, 12:39pm

On Sun, Jan 11, 2009 at 9:08 PM, Greg H.
[email protected] wrote:

Why does ActiveRecord allow perception of success when updating an ID,
however it doesn’t really work(i.e. no change in database)?

That is because :id is a special case and is protected from mass
assignment.

The reason it “works” or says that it does is because when you submit
an update form, you might have a params hash that looks like:

params[:account] #=> {:id => 2, :name => “Bob”}

and you will then do:

a = Account.find(params[:account][:id])
a.update_attributes(params[:account])

Now… in 99% of cases, you want this update_attributes command to
work, but you definately do NOT want some smartarse out there sending
in a carefully crafted web request that changes the ID value of the
account!

So that’s why, update_attributes “silently” ignores any attribute that
is protected from mass assignment.

Actually… it doesn’t ignore it. Look in your logs and you will see
something along the lines of “Can’t mass assign protected attribute
:id” or something.

For what it’s worth, doing:

account.update_attribute(:id, 1)

or

account.id = 1
account.save

Both work.

Hope that helps

Mikel

–

Rails, RSpec and Life blog…

greg · January 11, 2009, 12:46pm

thanks Mike - I was trying to setup a spec that tests that my foreign
key
constraints would hold - I’ll try the method you suggest

On Sun, Jan 11, 2009 at 9:38 PM, Mikel L. [email protected]
wrote:

an update form, you might have a params hash that looks like:
in a carefully crafted web request that changes the ID value of the

Hope that helps

Mikel

–
http://lindsaar.net/
Rails, RSpec and Life blog…

–
Greg
http://blog.gregnet.org/

greg · January 11, 2009, 12:49pm

PS. Just noted the other methods also don’t work fyi - see below. That
is
it doesn’t seem to be mass assignment related.
?> ai = AccountItem.find(:first)
=> #<AccountItem id: 1, account_id: 1, date: “2009-01-11”, amount:
#BigDecimal:22e80b8,‘0.1E2’,4(8), balance:
#BigDecimal:22e7f78,‘0.0’,4(8), description: “test”, notes: nil,
created_at: “2009-01-11 09:47:28”, updated_at: “2009-01-11 09:47:28”>

ai.id = 100000
=> 100000
ai
=> #<AccountItem id: 100000, account_id: 1, date: “2009-01-11”, amount:
#BigDecimal:22e34b4,‘0.1E2’,4(8), balance:
#BigDecimal:22e3374,‘0.0’,4(8), description: “test”, notes: nil,
created_at: “2009-01-11 09:47:28”, updated_at: “2009-01-11 09:47:28”>
ai.save
=> true

?> AccountItem.find(:all)
=> [#<AccountItem id: 1, account_id: 1, date: “2009-01-11”, amount:
#BigDecimal:22db098,‘0.1E2’,4(8), balance:
#BigDecimal:22daf58,‘0.0’,4(8), description: “test”, notes: nil,
created_at: “2009-01-11 09:47:28”, updated_at: “2009-01-11 09:47:28”>]

On Sun, Jan 11, 2009 at 9:38 PM, Mikel L. [email protected]
wrote:

an update form, you might have a params hash that looks like:
in a carefully crafted web request that changes the ID value of the

Hope that helps

Mikel

–
http://lindsaar.net/
Rails, RSpec and Life blog…

–
Greg
http://blog.gregnet.org/

greg · January 11, 2009, 1:33pm

a = Account.find(1)
new_account = Account.new(a.params)
new_account.id = new_id
new_account.save

should work

Well… it most definitely won’t…

You need:

new_account = Account.new(a.attributes)

and you might get further

–

Rails, RSpec and Life blog…

greg · January 11, 2009, 9:36pm

thanks - given all of this what do you think about the fact Rails
doesn’t
highlight the issue via exception? It still seems misleading to me the
way
it works…

On Sun, Jan 11, 2009 at 10:32 PM, Mikel L. [email protected]
wrote:

You need:

–
Greg
http://blog.gregnet.org/

greg · January 11, 2009, 1:32pm

Now… that is interesting

To be honest, I’ve only ever used setting the id to a specific value
on a new record… not on an existing one.

The problem is that the following code in
rails/activerecord/lib/base.rb is what does the update:

  def update(attribute_names = @attributes.keys)
    quoted_attributes = attributes_with_quotes(false, false,

attribute_names)
return 0 if quoted_attributes.empty?
connection.update(
"UPDATE #{self.class.quoted_table_name} " +
"SET #{quoted_comma_pair_list(connection, quoted_attributes)}
" +
“WHERE
#{connection.quote_column_name(self.class.primary_key)} =
#{quote_value(id)}”,
“#{self.class.name} Update”
)
end

As you can see, the WHERE clause is going to use id to find the record
we are after, as you set id to a different value… that won’t
work…

This code would have to be updated to allow id to be set using a
“new_id” and “old_id” value pair…

I think this is enough of an edge case though that you would be better
served by making a new record and deleting the old one…

like so:

a = Account.find(1)
new_account = Account.new(a.params)
new_account.id = new_id
new_account.save

should work

Mikel

–

Rails, RSpec and Life blog…