E.g. I have a model called Book which belongs_to model Shelf with fields :bookcase and :number.
I wonder, if I call to book.shelf.bookcase and then later to book.shelf.number does Rails actually load corresponding shelf each time? Or does it cache book.shelf somewhere? Shouldn't I make a new variable shelf = book.shelf and use shelf.bookcase and shelf.number instead?
Rails will cache association information, so you get whatever is in the cache when you access it. It does not reload it from the database each time.
There are cases when you do want a reload from the database, in which case the following syntax is used:
book.shelf(true).number
See section 3.1 in A Guide to Active Record Associations.
Related
I'm having trouble when querying Users.
My nesting resources are:
resources :users do
resources :photos do
resources :pins
end
end
1.) I have a user model, that has_many :photos.
2.) :photos has_many :pins
I want to list my users on which users have more pins in their photos.
So, I tried:
#members_ordered = User.includes(photos: :pins).group("users.id").group("photos.id").group("pins.id").order('COUNT(pins.id) DESC')
Not working though. Any ideas? Thanks guys
I have two observations, but neither directly fix the code in your example.
First, looking at my output from trying something similar, it seems like you either need quite complex SQL (which really isn't Rails' forte) or several simple queries (which, depending on the size of your app, could hit performance) to achieve this.
A little experimenting doesn't seem to show a significant difference (<1ms) in the time that one more complex query takes compared to that which three simple queries require (as in solution one)
Solution one, if performance is not crucial, for example, if this is a small, low-traffic solution, my instinct would be to add that the User model has_many :pins, through: :photos, which lets you call things like User.includes(photos: :pins).all, then user.pins.count, although, as I've mentioned, this causes a bit more database use.
Solution two, if performance is important, my suggestion would be to cache the count of pins against the user model. This could be as simple as an extra database column to store it, and have a background process (using delayed_job or similar) re-calculate the count each time it changes (so, maybe after_create in the Pin model.
The benefit of this is the slow, time-consuming query only gets run when the value changes, and the rest of the time, the value gets lifted from a single-table SELECT, which should take quite a bit less time than either solution one or the more complex query.
Both of these are less-than-perfect, and I think the most elegant and efficient way of working is to use a combination of a built-in function and a beautifully simple query:
The third solution, which brings together both of these options to some extent, is Rails' counter_cache option. As there are two levels to it, I can't see a native way to include all of these in one query, so we will automatically generate a count for each Photo, then add these up to get the User count.
Create a migration to add a pins_count field to the Photo model, so, in terminal, type;
rails g migration AddPinsCountToPhotos pins_count:integer
Update the belongs_to :photo line of the Pin model to;
belongs_to :photo, counter_cache: true
Now, every time a Pin gets created or deleted, the pins_count column of its Photo will be updated.
Now, to get the values for users;
Create a migration to add a pins_count field to the User model, so, in terminal, type;
rails g migration AddPinsCountToUsers pins_count:integer
Now we need to create an method in the Photo model, which we will run each time a pin is saved, so add this to your Photo model;
def update_user_counts
total_photos = self.user.photos.sum(:pins_count)
self.user.update_attribute(:pins_count, total_photos)
end
Finally, we need to tell Rails to call this whenever a pin is created or updated. We do this with a simple method that just calls the action from the Photo model;
after_save :update_photo_counts
def update_photo_counts
photo.update_user_counts
end
Now, whenever a pin is saved, it automatically updates the Photos pins_count, and then our new method totals the pins_counts from all of the Photos for that user, and saves them to the Users pins_count
I'm building a marketplace app. I have a Listing model (users list items to sell) and a User model. In the listing model, I have a userid column. And in the User model, I have a name field. In my listing show page, I want to display something like the below:
"Sold by #{#listing.user.name}"
But the join doesn't work in retrieving the name from the user table. If I change it to listing.userid then it works but I want to display the users name.
my user model has has_many :listings, dependent: :destroy
My listings model has belongs_to :user.
How can I display the user's name on the listing show page?
If you really have a column called userid instead of user_id then you have something very slightly different to what Rails expects... which is why Rails isn't finding it for you automatically.
Your best bet is to rename the column (using a migration) to user_id to take advantage of the Rails default behaviour. Trust me - it's worth the effort up front if you can do this.
If for some odd reason you can't (serious business constraints), then there are ways of telling rails that you are using a non-standard foreign-key... but lets not get to that unless you have to.
I am trying to create an invoicing system that does not persist to a database, but passes through to a third party system. Hence, my models are not ActiveRecord as there is no table to persist to. How can I accept nested attributes for invoice line items in my invoice model?
This is an example of the resulting params from my form
{"payportal_invoice"=>{"invoice_lines"=>{"quantity"=>["1", "2"], "units"=>["hours", "hours"], "price"=>["10", "20"], "description"=>["desc", "d"]}, "dueDate"=>"10/10/2013", "invoiceNumber"=>"3.13.13.11:47", "description"=>"notes"}, "attachment_name"=>""}
I can easily create the invoice model from this params set, but am not sure how to create the line items
Have you tried using a tableless gem, such as https://github.com/softace/activerecord-tableless?
I've used them for similar situations in the past - you can do all of the standard validations, etc, but without needing to invoke ActiveRecord.
I have an Activity stream I have designed using STI in rails 3.
I want to do a check to see if a user has more than 10 activity items on create. When a user creates his 11th Activity in the database, I want it to destroy the oldest record * essentially the first record the user made and so on.* This way I am keeping my database clean of thousands of old useless records.
I am assuming I would start at the model level, but since I dont want to define the "current_user" in the model, it should be in the controller.
Any help would be appreciated to accomplish this task, I am fairly new at these type of more advanced tasks in rails.
You can hook this logic up in an AR callback. Assuming you kept rails conventions when modeling you classes, and each activity belongs to a user, you can then easily do the following in your Activity model:
after_save do |record|
if Activity.where(:user => record.user).count >= 11
Activity.where(:user => record.user).order('created_at asc').first.destroy
end
end
I guess this will create three transactions to the db (one for count, another to find the first record, and one to delete it). I wonder if there's a more efficient way to do this, as it will be invoked on every Activity#save...
I have a Record model and I want to create a Field model such that a given Record has_many Fields. Similarly I want each field to be associated with a Tag such that each Field has_one Tag. But each Tag can be reused many times between Field objects.
In this case would I just say that a Tag belongs_to_many Fields? Likewise would it be right to say that the Field belongs_to_many Records?
(Ultimately I want the Record object to be a container for multiple Fields. I envision having a form where I can dynamically add new Field and Tag, so that a Record might look like:
Record 1
Tag 1
Field 1
Tag 2
Field 2
...
where each Tag can either be pulled from a pre-existing pool or created on the fly) Thanks for the help!
First, I would highly recommend reading RoR Guide on Associations:
http://guides.rubyonrails.org/association_basics.html
Whether you are new or need a touch up on using Associations in RoR, read that guide.
Your question seems to be more of a logic question, but I'll start with the
code for it:
class Record < ActiveRecord::Base
has_and_belongs_to_many :fields
...
class Field < ActiveRecord:Base
has_and_belongs_to_many :records
belongs_to :tag
...
class Tag < ActiveRecord:Base
has_many :fields
...
Each Record connects to many different fields, and each field connects to many different Records. This is a classic example of a many to many association. The logic in your code when you actually use these models is what will make the Record Model seem like a container (Because technically you could say a Field is a container for many records).
Each Field will have 1 Tag associated with it, but that same Tag could be used with any number of fields (You could say the Fields are reusing the tags). This is a one to many association. When making this connection you would use belongs_to in the Field model, and has_many in the Tag model.
Since Tag is connected to the Field Model, the logic you are looking for: A Record is a container for Fields and Tags, makes sense with this setup.
Here is a simple example of fetching a Tag inside a record:
#Returns the Tag Associated with the first field
#"inside" the first Record in the database.
Record.first.fields.first.tag
Likewise, one could easily go the opposite direction:
Tag.first.fields.first.records.first
Make sure to leverage the Rails commands via command line to quickly setup your migrations and models. As far as options on how you want your associations to handle things when one as deleted, saved, and so on, just read the guide at the top to find what you are looking for.