On Tuesday, 20 January 2015 10:56:09 UTC+1, Colin Law wrote:
>
> On 20 January 2015 at 09:25, Javix <s.ca...@gmail.com <javascript:>>
> wrote:
> >
> >
> > On Tuesday, 20 January 2015 10:15:17 UTC+1, Colin Law wrote:
> >>
> >> On 20 January 2015 at 09:04, Javix <s.ca...@gmail.com> wrote:
> >> > I wonder id it is normal behaviour that when building an assosiation
> >> > 'build'
> >> > method , the returned size of association array changes despite the
> >> > objet is
> >> > nt saved yet ? Here is a short exampe to illustrate that:
> >> >
> >> > class User < ActiveRecord::Base
> >> > has_many :posts, dependent: :destroy
> >> > end
> >> >
> >> > class Post < ActiveRecord::Base
> >> > belongs_to :user
> >> > end
> >> >
> >> > Nothing complex until now. When I play with that in the console:
> >> > Loading development environment (Rails 4.2.0)
> >> > irb(main):001:0> user = User.first
> >> > User Load (0.0ms) SELECT "users".* FROM "users" ORDER BY
> >> > "users"."id"
> >> > ASC LIMIT 1
> >> > => #<User id: 1, name: "toto", created_at: "2015-01-16 11:18:41",
> >> > updated_at: "2015-01-16 11:18:41">
> >> > irb(main):002:0> user.posts.size
> >> > (0.0ms) SELECT COUNT(*) FROM "posts" WHERE "posts"."user_id" = ?
> >> > [["user_id", 1]]
> >> > => 0
> >> > irb(main):003:0> post = user.posts.build(title: 'ruby')
> >> > => #<Post id: nil, user_id: 1, title: "ruby", created_at: nil,
> >> > updated_at:
> >> > nil>
> >> > irb(main):004:0> user.posts.size
> >> > => 1
> >> > irb(main):005:0>
> >> >
> >> > As you see the size of user posts is changed by 1. Why ? The post is
> not
> >> > still saved to the database. The user_id is nil. I had to apply some
> >> > validation before adding a new post tp ths user, that's why I wonder
> if
> >> > it
> >> > is normal adn how to display just the existing User posts without
> using
> >> > 'select' for example.
> >>
> >> You have not saved it to the database but you have added it to the
> >> users posts in memory. If you reload user it will revert to 0, and
> >> you will lose the built post. If you want to check what it is in the
> >> database then fetch the user to a new variable.
> >> user1 = User.first
> >> then user1.posts.size will be 0
> >>
> >> Colin
> >
> >
> > So it is normal because AR does not make a new query to the DB and
> operates
> > on the existing cached collection. What if instead of making the same
> query
> > to find the same user:
> >
> > user1 = User.first
> >
> > I'll do like that:
> > user.posts(force_reload: true).size
> >
> > it works as needed and it seems like force_reload is false by default.
> What
> > do you think ?
>
> I think just user.reload would do it. It is not something I have had
> to do often, why would one build an association and then want to throw
> it away again in the same action?
>
Why do I want it - because I'd like to run a validation callback before
saving an element of the collection. For example, an Account has_many
Operations. So I create an Operation like that in the OperationsController:
def create @operation = @account.operations.new(operation_params) if
@operation.save redirect_to @account, notice: t(:created_success,
model: Operation.model_name.human) else
render "new" end end
What I'd like to do is to check the sum to be withdrawn in the above
operation so that the balance of the account not to be negative. That's how
I
discovered the described behaviour.
> Colin
>
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