Hi for rails model association, i know i can do this:
For example a model class Page.
class Page < ActiveRecord::Base
has_many :parts
end
I can do this:
Page.first.parts.find_by_name('body')
Page.first.parts.class actually returns Array. How can it activate methods for Part model? I found the similar post on How do rails association methods work?
My question is that when i try to use memcache to cache the response for parts methods. Then when i call Page.first.parts.find_by_name('body'), it tells me that the Array doesn't have method find_by_name. How do i solve this problem? I need to have the cache as this is one heavily used methods.
class Page
def parts_with_cache
Rails.cache.fetch("parts_for_page_#{id}", {:expires_in => 1.minutes}) do
parts_without_cache
end
end
alias_method_chain :parts, :cache
end
Since you are getting back an array of Parts objects associated to the Page object unfiltered by part name, just do an Array select method on the result set.
body_parts = Page.first.parts.select{ |part| part.name == 'body' }
Related
I have a couple of models that are composites of multiple objects. I basically manage them manually for saves and updates. However, when I select items out, I don't have access to the associated properties of said item. For example:
class ObjectConnection < ActiveRecord::Base
def self.get_three_by_location_id location_id
l=ObjectConnection.find_all_by_location_id(location_id).first(3)
r=[]
l.each_with_index do |value, key|
value[:engine_item]=Item.find(value.engine_id)
value[:chassis_item]=Item.find(value.chassis_id)
r << value
end
return r
end
end
and each item:
class Item < ActiveRecord::Base
has_many :assets, :as => :assetable, :dependent => :destroy
When I use the ObjectLocation.find_three_by_location_id, I don't have access to assets whereas if use Item.find(id) in most other situations, I do.
I tried using includes but that didn't seem to do it.
thx
Sounds like the simplest solution would be to add methods to your ObjectConnection model for easy access like so:
class ObjectConnection < ActiveRecord::Base
def engine
Engine.find(engine_id)
end
def chassis
Chassis.find(chassis_id)
end
# rest of class omitted...
I'm not exactly sure what you're asking... If this doesn't answer what you're asking, then can you try to be a little bit more clear with what exactly you are trying to accomplish? Are the Chassis and Engine mdoels supposed to be polymorphic associations with your Item model?
Also, the code you're using above won't work due to the fact that you are trying to dynamically set properties on a model. It's not your calls to Item.find that are failing, it's your calls to value[:engine_item]= and value[:chassis_item] that are failing. You would need to modify it to be something like this if you wanted to keep that flow:
def self.get_three_by_location_id location_id
l=ObjectConnection.find_all_by_location_id(location_id).first(3)
r=[]
l.each_with_index do |obj_conn, key|
# at this point, obj_conn is an ActiveRecord object class, you can't dynamically set attributes on it at this point
value = obj_conn.attributes # returns the attributes of the ObjectConnection as a hash where you can then add additional key/value pairs like on the next 2 lines
value[:engine_item]=Item.find(value.engine_id)
value[:chassis_item]=Item.find(value.chassis_id)
r << value
end
r
end
But I still think that this whole method seems unnecessary due to the fact that if you setup proper associations on your ObjectConnection model to begin with, then you don't need to go and try to handle the associations manually like you're attempting to do here.
Consider a simple example, where we have 2 models, Article and Category.
class Article < ActiveRecord::Base
belongs_to :category
def self.search(title)
where(:title => title)
end
end
class Category < ActiveRecord::Base
has_many :articles
end
Now, on the rails console :
Article.all.search('test article')
As expected returns an error
NoMethodError: undefined method `search' for #<Array:0x9aa207c>
But when I do this
Category.first.articles.search('test article')
returns a set of records!
This prompts a check on the classes of
Article.all
and
Category.first.articles
both returning the Array class.
Obviously, Article's class method 'search' is being inducted in run time and prompting a 'correct' return of records when accessed through its association (Category) but behaving otherwise when accessed by the class itself (Article).
So, What's happening?
This is because when you perform .all the query is actually executed, so the object returned will be a basic array. However, when you perform Category.first, it will return a Category object, then articles is actually making use of ActiveRecord::Reflection::AssociationReflection and doing an extension of an Array. For example, in rails c try:
Category.first.articles.ancestors
vs
Category.first.articles.all.ancestors #throws an error
The second one throws an error, because at this point the object is just a simple Array. The first, however, is made up of something like this:
Article(...), ActiveRecord::Base, ActiveRecord::Reflection, Object (and so on)
As another example, try this:
a = Category.first.articles; ObjectSpace.each_object(Class).select {|k| a < k }
#=> [Object, BasicObject, ActiveRecord::Base]
You can see that although it looks like an Array, it's inheriting those other classes.
Article.all
This returns an array that's giving you the error as you saw, you're trying to run a class function of Article on the Array class.
I'm not sure what exactly you're trying to accomplish but you could do this, I think
Article.search("soem content")
However, I'm not sure if that would return a result, as it might just return an
I'm trying to override the way rails apply and id to an associated object, for example:
There are 2 simple models:
class Album < ActiveRecord::Base
has_many :photos
end
class Photo < ActiveRecord::Base
belongs_to :album
end
And then I want to do this:
album = Album.new :title => 'First Album'
album.photos.build
album.save #=> true
On this case I've created a plugin that overrides the id property and replaces it to a hashed string, so what I want to do is find the methods where this album_id is being replaced for my custom method instead of the int and be able to converted before it's saved.
But I want to act globally inside Rails structure because since it will be a sort of plugin I want to make this action work on dynamic models, that's why I can't create an before_save validation on the model.
I'm not sure if it's easy to understand, but I hope someone could help me on that..
Here's a screenshot of my current table so you can see what is happening:
SQLite3 DB http://cl.ly/1j3U/content
So as you can see the album_id it's being replaced for my custom ruby object when its saved...I've disabled the plugin and then it saved normally with records 11 and 12...
I want just act on a rails action and converted with my custom methods, something like
def rails_association_replaced_method(record)
#take the record associations and apply a to_i custom method before save
super(record)
end
something like this :)
Well I hope this didn't get too complicated
Cheers
It seems if I only override theActiveRecord::Base save method do the job if handled properly
define_method 'save' do
int_fields = self.class.columns.find_all { |column| column.type == :integer }
int_fields.each do |field|
if self.attributes[field.name]
self.attributes[field.name] = self.attributes[field.name].to_i
end
end
super
end
And this shall replace all the integer fields from the Current Model applying a to_i method over the result.
Rails is unfriendly to that kind of change to the defaults. What's your end goal here?
I have the following one to many associations. Document has many Sections and Section has many Items.
class Document < ActiveRecord::Base
has_many :document_sections, :dependent => :destroy, :autosave => true
has_many :document_items, :through => :document_sections
end
class DocumentSection < ActiveRecord::Base
belongs_to :document
has_many :document_items, :dependent => :destroy, :autosave => true
end
class DocumentItem < ActiveRecord::Base
belongs_to :document_section
end
Here is the params hash:
-
Parameters: {"commit"=>"Submit Document", "authenticity_token"=>"4nx2B0pJkvavDmkEQ305ABHy+h5R4bZTrmHUv1setnc=", "id"=>"10184", "document"=>{"section"=>{"10254"=>{"seqnum"=>"3", "item"=>{"10259"=>{"comments"=>"tada"}}}}, "comment"=>"blah"}}
I have the following update method...
# PUT /documents/1
# PUT /documents/1.xml
def update
#document = Document.find(params[:id])
# This is header comment
#document.comment = params[:document][:comment]
params[:document][:section].each do |k,v|
document_section = #document.document_sections.find_by_id(k)
if document_section
v[:item].each do |key, value|
document_item = document_section.feedback_items.find_by_id(key)
if document_item
# This is item comments
document_item.comments = value[:comments]
end
end
end
end
#document.save
end
When I save the document it only updates the document header comments. It does not save the document_item comments. Shouldn't the autosave option also update the associations.
In the log only the following DML is registered:
UPDATE documents SET updated_at = TO_DATE('2010-03-09 08:35:59','YYYY-MM-DD HH24:MI:SS'), comment = 'blah' WHERE id = 10184
How do I save the associations by saving the document.
I think I see what the problem is. I'm pretty sure that you cannot do the following:
# Triggers a database call
document_section = #document.document_sections.find_by_id(k)
And expect ActiveRecord to keep the association for autosaves. Instead, you should save the loaded records individually. Which of course would not be atomic.
I believe for autosave to work like you are thinking, you want to do something like this:
# untested...
#document.document_sections.collect { |s| s.id == k }.foo = "bar"
Notice that here I'm actually modifying a fake param foo in the array, instead of calling find_by_id, which will re-query the database and return a new object.
A third option you have is that you could of course, do what you had originally planned, but handle all the transactions yourself, or use nested transactions, etc, to get the atmoic saves. This would be necessary if your data was too large for array manipulation to work since autosave by it's natures triggers a load of all associated data into memory.
It all depends on your application.
Some clarifications on the underlying problem:
If you run the find_by_id method, you are asking ActiveRecord to return to you a new set of objects that match that query. The fact that you executed that method from an instance (document_sections) is really just another way of saying:
DocumentSection.find_by_id(k)
Calling it from an object instance I think is just some syntactic niceness that rails is adding on the top of things, but in my mind it doesn't make a lot of sense; I think it could be handy in some application, I'm not sure.
On the other side, collect is a Ruby Array method that offers a way to "slice" an array using a block. Basically a fancy foreach loop. :) By interacting with the document_sections array directly, you are changing the same objects already loaded into the containing object (#document), which will then be committed when you save with the special autosave flag set.
HTH! Glad you are back and running. :)
Updated
Appears to be a precedence error and nothing to do with the question I originally asked. See discussion below.
Original question
Is it possible to use active record associations in callbacks? I've tested this code in the console and it works fine as long as it isn't in a callback. I'm trying to create callbacks that pull attributes from other associated models and I keep getting errors of nil.attribute.
If callbacks are not the correct approach to take, how would one do a similar action in rails? If the associations are simple, you could use create_association(attributes => ), but as associations get more complex this starts to get messy.
For example...
class User < ActiveRecord::Base
belongs_to :b
before_validation_on_create {|user| user.create_b} #note, other logic prevents creating multiple b
end
class B < ActiveRecord::Base
has_many :users, :dependent => destroy
after_create{ |b| b.create_c }
has_one :c
end
class C < ActiveRecord::Base
belongs_to :b
after_create :create_alert_email
private
def create_alert_email
self.alert_email = User.find_by_b_id(self.b_id).email #error, looks for nil.email
end
end
Off course associations are available in your callbacks. After all, the create_after_email is simply a method. You can even call it alone, without using a callback. ActiveRecord doesn't apply any special flag to callback methods to prevent them from working as any other method.
Also notice you are running a User#find query directly without taking advantage of any association method. An other reason why ActiveRecord association feature should not be the guilty in this case.
The reason why you are getting the error should probably searched somewhere else.
Be sure self.b_id is set and references a valid record. Perhaps it is nil or actually there's no User record with that value. In fact, you don't test whether the query returns a record or nil: you are assuming a record with that value always exists. Are you sure this assumption is always statisfied?