I want to debug a messy app and I want to see the effective model configuration
Is there a way to see what rails know about a model in terms of its associations?
for example - if I have
class User
has_many :comments, :dependent => :destroy
end
I'd like to see that rails know that it will call the destroy action in the comment controller if destroy action is called in users controller
Is there a way to see in rails console?
got it,
it can be done with
User.reflections
which results in
:comments=>
#<ActiveRecord::Reflection::AssociationReflection:0xc52abc8
#active_record=
User(id: integer, ...)
#collection=true,
#macro=:has_many,
#name=:comments,
#options={:dependent=>:destroy, :extend=>[]},
#plural_name="comments">
which, as you can see, gives you the type of association (has_many), what it is called (:comments), the options and the plural name.
I am in :love: with this method :)
Related
I'm working on a Rails 3.0.x application (actually it's Hobo 1.3.x but that's not material to this question). Among the models, there are GraphPanes, GraphLabels, and LabelSets. A GraphPane can have GraphLabels and LabelSets. GraphLabels can belong to GraphPanes or LabelSets, but not both. So if a GraphLabel belongs to a LabelSet, I'd like to keep it from being associated to a GraphPane.
I am trying to enforce that with this code in the GraphPane model:
has_many :graph_labels, :conditions => 'label_set_id = NULL'
However, I'm still able to associate GraphLabels with not-null label_set_id with GraphPanes. Why? How can I stop this?
This question is superficially similar, but my relationship isn't polymorphic, so the nominal solution there doesn't help me.
The functionality of :conditions on has_many is to filter the results that are passed back via the graph_labels, not to protect objects from being added to the association.
If you add a graph_label with no label_set_id, the association will build, but if you then ask for graph_pane.graph_labels, it will not return that non-condition-matching graph_label.
The has_many/belongs_to relationship is saved on the belongs_to model, graph_label, and so the parent/has_many/graph_pane does not stop the graph_label from writing whatever it wants to its graph_pane_id attribute. This delegation of responsibility is correct, although frustrating, I agree.
Now, as for how to stop this, I'm not sure. It sounds like you need some sort of validation on the graph_label object, something along the lines of not allowing a graph_pane_id to be set on a graph_label if that graph_label's label_set_id is nil. Since the has_many/belongs_to relationship is saved on the graph_label, you should write the validation on the graph_label. That way, the graph_label will not be able to be saved with a new graph_panel_id unless it fulfills the condition.
Thoughts? Questions?
Reference:
has_many
Alternate Solution
I've reread your question and I think want you want here is a polymorphic association.
def GraphPane < ActiveRecord::Base
has_many :label_sets
has_many :graph_labels, as: :parent
end
def LabelSet < ActiveRecord::Base
belongs_to :graph_pane
has_many :graph_labels, as: :parent
end
def GraphLabel < ActiveRecord::Base
belongs_to :parent, polymorphic: true
end
That way, a GraphLabel can only have a single parent, which is what your “spec” above requires. Is there any reason not to implement the relations in this way?
I have a datamodel that contains a Project, which contains a list of Suggestions, and each Suggestion is created by a User. Is there a way that I can create a list of all distinct Users that made Suggestions within a Project?
I'm using Mongoid 3. I was thinking something like this, but it doesn't work:
#project = Project.find(params[:id])
#users = Array.new
#users.push(#project.suggestions.user) <-- this doesn't work
Any ideas? Here's my model structure:
class Project
include Mongoid::Document
has_many :suggestions, :dependent => :destroy
...
end
class Suggestion
include Mongoid::Document
belongs_to :author, class_name: "User", :inverse_of => :suggestions
belongs_to :project
...
end
class User
include Mongoid::Document
has_many :suggestions, :inverse_of => :author
...
end
While Mongoid can give MongoDB the semblance of relationships, and MongoDB can hold foreign key fields, there's no underlying support for these relationships. Here are a few options that might help you get the solution you were looking for:
Option 1: Denormalize the data relevant to your patterns of access
In other words, duplicate some of the data to help you make your frequent types of queries efficient. You could do this in one of a few ways.
One way would be to add a new array field to User perhaps called suggested_project_ids. You could alternatively add a new array field to Project called suggesting_user_ids. In either case, you would have to make sure you update this array of ObjectIds whenever a Suggestion is made. MongoDB makes this easier with $addToSet. Querying from Mongoid then looks something like this:
User.where(suggested_project_ids: some_project_id)
Option 2: Denormalize the data (similar to Option 1), but let Mongoid manage the relationships
class Project
has_and_belongs_to_many :suggesting_users, class_name: "User", inverse_of: :suggested_projects
end
class User
has_and_belongs_to_many :suggested_projects, class_name: "Project", inverse_of: :suggesting_users
end
From here, you would still need to manage the addition of suggesting users to the projects when new suggestions are made, but you can do so with the objects themselves. Mongoid will handle the set logic under the hood. Afterwards, finding the unique set of users making suggestions on projects looks like this:
some_project.suggesting_users
Option 3: Perform two queries to get your result
Depending on the number of users that make suggestions on each project, you might be able to get away without performing any denormalization, but instead just make two queries.
First, get the list of user ids that made suggestions on a project.
author_ids = some_project.suggestions.map(&:author_id)
users = User.find(author_ids)
In your Project class add this :
has_many :users, :through => :suggestions
You'll then be able to do :
#users.push(#project.users)
More info on :through here :
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#method-i-has_many
For mongoid, take a look at this answer :
How to implement has_many :through relationships with Mongoid and mongodb?
I have been breaking my head around this for a long time now. Not sure if my approach is correct or if its not possible using mongoid. SO without further adieu, here is the problem:
I have the following 2 models:
def user
embeds_many :needs, :class_name => "Property"
embeds_many :skills, :class_name => "Property"
end
def property
end
Both these models of course have other code but I have skipped that for brevity.
With this structure I am able to access/add "Property" data as embedded "needs" & "skills" on my user model. Something like this works flawlessly
User.first.update_attributes(skills: [Property.first])
The problem is something like this doesn't work.
User.first.skills.push(Property.first)
User.first.skills << Property.first
There is no error. Both the above statements return true on console. But the values don't persist to the DB.
I basically want a Property model which can be maintained/created independent of the User model, thats why the "embedded_in" on Property is missing in my code.
The question is, am I doing it right? Or there is their a different way that I should go about the design of these models?
Cage is right. You will need to put the embedded_in on the Property model if you want the persistence to work properly. If you want to manage the lifecycle of Property outside the User model, you will have to use 'has_many'.
Please add more details as to what exactly is the purpose of doing what you are doing. I am going to make some assumptions-
Needs and skills are a global list of values, that should be maintained separately
User can have a subset of skills and needs
You want to store the needs and skills as 'plain string' and not references so you can query them without referencing the needs and skills collection. This reduces one query
If the above is correct, then you can use custom keys to store the needs and skills-
class Property
include Mongoid::Document
field :text, :type => String
field :_id, type: String, default ->{ text }
end
class User
include Mongoid::Document
has_many :needs, :class_name => "Property"
has_many :skills, :class_name => "Property"
end
Now you can do something like-
User.first.need_ids
This will give the text of the need and you can avoid another query.
Note- that this is potentially very risky if your 'Property' objects are mutable.
For solution try doing this
u = User.first
u.skills.push(Property.first)
u.skills << Property.first
it will work fine.
I made a relationship with the three models using has_many :through:
class Curriculum class < ActiveRecord::Base
has_many :interests
has_many :vacancies,: through => :interests
end
class Vacancy class < ActiveRecord::Base
has_many :interests
has_many :resumes,: through => :interests
end
class Interest < ActiveRecord:: Base
belongs_to :vacancy
belongs_to :curriculum
end
And to create curriculum and vacancy, I create them by administrative, i need to know how can i create the interest to the id of the vacancy, and how it will be logged on the system I have to get the id of it and make the relationship in creating a new bank interest. I wonder how I can program it to do so, and I wonder how the controller will get the create action, and what better way to do this.
First, try to read the whole "Guide to Rails on Associations", especially the part about has_many :through. Then check your schema if your db is migrated and contains for the table interests the necessary foreign keys to curriculums and vacancies called curriculum_id and vacancy_id.
If that is all in place, the following code will create the relationship between two objects:
#curr = Curriculum.find(1)
#vac = Vacancy.find(1)
#curr.interests << #vac
#curr.save
The last two lines creates an interest between #curr and #vac and store that on the database. So you should not use IDs and handle them directly, but work with objects instead.
The second part now is to provide a UI to allow the definition (and removal) of interests between curricula and vacancies. The base flow here is:
You have one curriculum in focus.
You have a link to add / remove curricula.
The view that opens shows a list of possible vacancies, where every vacancy has a checkbox.
By selecting (or deselecting) the check boxes, the IDs of the vacancies will be held in the params of the request sent to the controller.
See the (older) podcast Railscast #52 how to do that in a similar context. Or see the example for has_many :through with checkboxes.
An alternative way would be to use JQuery autocomplete, and add so interests one-by-one. See the nice podcast Railscast #258 which uses JQuery Tokeninput for that.
I think this is what your looking for:
HABTM Checkboxes
That's the best way to use an Has and Belongs to many association.
Suppose I have the following model relationship:
class Player < ActiveRecord::Base
has_many :cards
end
class Card < ActiveRecord::Base
belongs_to :player
end
I know from this question that Rails will return me a copy of the object representing a database row, meaning that:
p = Player.find(:first)
c = p.cards[0]
c.player.object_id == p.object_id # => false
...and therefore if the Player model modifies self, and the Card model modifies self.player in the same request, then the modifications won't take any notice of each other and the last-saved one will overwrite the others.
I'd like to work around this (presumably with some form of caching), so that all requests for a Player with a given id would return the same object (identical object_ids), thereby allowing both models to edit the same object without having to perform a database save-and-reload. I have three questions:
Is there already a plugin or gem to do this?
Are there good reasons why I shouldn't do this?
Can anyone give me some pointers on how to go about doing this?
This is supported in Rails 3.x. You can use the :inverse_of option for the has_many association for example. Documentation here (search for :inverse_of and Bi-directional associations).