I''m a beginner to both Ruby and Rails and I''m currently reading the Agile development with Rails, in which I''m currently developing the cart of the store. I have a *line_items* model which *belongs_to :products*. This makes sense. Later in the example we use this code to check if a product is referenced by any line items before we destroy it: class Product < ActiveRecord::Base has_many :line_items before_destroy :ensure_not_referenced_by_any_line_item private # ensure that there are no line items referencing this product def ensure_not_referenced_by_any_line_item if line_items.empty? return true else errors.add(:base, ''Line Items present'') return false end end end This makes sense to me except of one part: if line_items.empty? I can only guess that *line_items *returns all the rows of the "line_items" table that contain the product.id of the currently instantiated Product object, is that right? But how does the model knows what to fetch just by "line_items"? Isn''t that too little info that we give to our model, regarding the logic of the task it has to do? Don''t we have to declare somewhere something like: *return false if line_items.product.id == product.id* ? Thanks in advance people! -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To view this discussion on the web visit https://groups.google.com/d/msg/rubyonrails-talk/-/4LQoGwJO8J8J. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
On 17 January 2012 11:47, Agis A. <corestudiosinc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:> I''m a beginner to both Ruby and Rails and I''m currently reading the Agile > development with Rails, in which I''m currently developing the cart of the > store. > > I have a line_items model which belongs_to :products. This makes sense. > Later in the example we use this code to check if a product is referenced by > any line items before we destroy it: > > class Product < ActiveRecord::Base > > has_many :line_items > > before_destroy :ensure_not_referenced_by_any_line_item > > private > > # ensure that there are no line items referencing this product > > def ensure_not_referenced_by_any_line_item > > if line_items.empty? > > return true > > else > > errors.add(:base, ''Line Items present'') > > return false > > end > > end > > end > > > This makes sense to me except of one part: if line_items.empty? I can only > guess that line_items returns all the rows of the "line_items" table that > contain the product.id of the currently instantiated Product object, is that > right? But how does the model knows what to fetch just by "line_items"? > Isn''t that too little info that we give to our model, regarding the logic of > the task it has to do? Don''t we have to declare somewhere something like: > return false if line_items.product.id == product.id ?The fact that you have said has_many :line_items automatically makes a method line_items available for any product that returns an array (actually it is not strictly an array, but near enough) containing all the line items for that product. Similarly if you have a line item in @line_item then you can say @line_item.product to get the associated product. Have a look at the Rails Guide on ActiveRecord associations to find all the methods that rails makes available. Colin -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
I see. Now I''ve upgraded my seeds.rb file, to add some entry into the line_items table and see how it works. Actually I''ve added this line: *LineItem.create (product_id: ''8'', cart_id: ''1'')* * * but when I run rake db:seed I get this error: rake db:seed> rake aborted! > /rails/depot/db/seeds.rb:55: syntax error, unexpected tLABEL > >> LineItem.create (product_id: 8, cart_id: 1) > > ^My migration file for LineItems table is this:> class CreateLineItems < ActiveRecord::Migration > def change > create_table :line_items do |t| > t.integer :product_id > t.integer :cart_id > t.timestamps > end > end > end-- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To view this discussion on the web visit https://groups.google.com/d/msg/rubyonrails-talk/-/f4XlY7oLa7gJ. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
On Tue, Jan 17, 2012 at 1:05 PM, Agis A. <corestudiosinc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:> I see. > > Now I''ve upgraded my seeds.rb file, to add some entry into the line_items > table and see how it works. > Actually I''ve added this line: *LineItem.create (product_id: ''8'', > cart_id: ''1'')* > * > * > but when I run rake db:seed I get this error: > > rake db:seed >> rake aborted! >> /rails/depot/db/seeds.rb:55: syntax error, unexpected tLABEL >> >>> LineItem.create (product_id: 8, cart_id: 1) >> >>Remove the space before the ''('' LineItem.create(product_id: 8, cart_id: 1) In newer versions of Ruby (1.9.3 and maybe earlier), this is not longer allowed. Peter -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.