I'm trying to create an association for a beta meat-sale application between one model, Cuts, and the "animal_type" attribute of another model, Animal, such that I could list all the cuts associated with a particular animal_type (or associated with an animal that has that type as an attribute).
In other words, if animal_type is "cow", I should be able to call up a list of all the cuts (ribeye, tenderloin, etc) associated with cows. I'm new to Rails, and this is fairly above my head.
My idea was to create an animal_type column in Cuts and Animals, to associate each cut with a type of animal, so I could do something along the lines of
#cuts = Cut.where(:animal_type => Animal::animal_type[:Cow])
No idea if that works, though, and what else I need to do to make this association possible. Can anybody help point me towards a way of thinking this through? Or does anyone have any good resources I could look at to help me with this specific problem? I've been looking through Rails Guides, and they're helpful, but they don't really give me a way to answer this.
You could have a Cuts model and an Animal model. Cuts could have a string attribute called "name" which would store the cut type such as ribeye, tenderloin etc. Animal could have a string attribute called animal_type. You could then setup a has_many association between Animals and Cuts. Something like this:
class Animal < ActiveRecord::Base
attr_accessible :animal_type
has_many :cuts
end
class Cuts < ActiveRecord::Base
attr_accessible :name
belongs_to :animals
end
This should be a good start
Related
Consider this setup. Please understand that our setup is much more detailed but this is a simple example.
competition which has name. This is an annual competition.
competition_instances which has location, starts_at.
Each competition has sports which has name.
Example:
competition.name: "Super Bowl" has different competition_instances every year but sport remains the same.
Conversely, competition.name: "Olympics" has different competition_instances and different sports in each competition_instance.
Would it be best to create competition_sports and competition_instance_sports with competition_instance_sports as a subclass of competition_sports?
GOAL: Use competition_instance_sports records if they exist, otherwise use the competition_sports record. In our real world app, each competition/competition_instance can have 20-50 sport records. How can we best achieve?
Based on what I understand from the question I cannot see where STI will be helpful in this situation. However a join table will get you where you want.
I suggest creating a new table sports, this model will have all the specific details of each sport. The competition_instance.rb will have one/many sport.rb. competiton.rb will have many sports through competition_instance.rb.
competition.rb
Class Competition < ActiveRecord::Base
has_many :competition_instances
has_many :sports, through: :competition_instances
end
competition_instance.rb
Class CompetitionInstance < ActiveRecord::Base
belongs_to :competition
belongs_to :sport
end
sport.rb
Class Sport < ActiveRecord::Base
has_many :competition_instances
end
By using this design you will be able to achieve the following:
1- You will have your predefined sports in your database along with their specific properties.
2- Each competition will have .sports which will give all the sports in this competition for the olympics case.
3- You will be able to set specific properties for each competition instance (example event_start_time and event_end_time) in the competition instance table.
I'm just thinking of the case where there are standard sports which are always in the Olympics and some which are added on, such as those proposed by the host country.
I would use Polymorphic Associations, in a "reverse manner".
class Competition < ActiveRecord::Base
has_many :competition_instances
has_many :competition_sports, as: :event
end
class CompetitionInstance < ActiveRecord::Base
belongs_to :competition
has_many :competition_sports, as: :event
def events_array # neater by sacrificing ActiveRecord methods
competition.competition_sports + competition_sports
end
def events # messier, returns ActiveRecord relationship
CompetitionSport.where( " ( event_id = ? AND event_type = 'Competition' ) OR
( event_id = ? AND event_type = 'CompetitionInstance')", competition_id, id )
end
end
class Sport < ActiveRecord::Base
has_many :events, as: :competition_sport
end
class CompetitionSport < ActiveRecord::Base
belongs_to :sport
belongs_to :event, polymorphic: true
end
This allows:
competition.competition_sports # standard sports
competition_instance.competition_sports # only those specific for this instance
competition_instance.events # includes sports from both
Aiming at the original question of "Is this a use case for STI", it will be difficult to say if this is or not without seeing the full complexity of your environment. But here's are some things to consider:
Abridged from How (and When) to Use Single Table Inheritance in Rails - eugenius blog:
STI should be considered when dealing with model classes that share much of the same functionality and data fields, but you want more granular control over extending or adding to each class individually. Rather than duplicate code or forego the individual functionalities, STI permits you to use keep your data in a single table while writing specialized functionality.
You've simplified your example, but it sounds like competition and competition_instance are NOT essentially the same object, with minor behavioral differences. With what you've described, I would probably rename these objects to event and competition, or whatever makes better sense to you in terms of illustrating what these objects are actually representing. I think of 'The Olympics' as a generic event, and '100m Dash' as a competition taking place at The Olympics. Or "The SuperBowl" only hosted one competition in 2014, "SuperBowl XLIX".
You've also tagged this question with database-normalization, which STI won't help. If the attributes differ slightly between your shared objects you'll end up with null fields everywhere.
I refer you to the other answers here to see how you should probably set those objects up to behave as desired.
This is not a case for single table inheritance, because competition_instance is not a substitute for competition and 1 competition can have many competition_instances. So you have 3 tables:
competitions
sports
competition_instances
competition_instances has a foreign key to competitions because 1 competition can have many competition_instances but each competition_instance has exactly one competition.
Whether you attach sports to competitions or competition_instances depends on the specific constraints of your use case. I don't exactly know what you mean by "each competition/competition_instance can have 20-50 sport records". I would expect each competition_instance to have exactly one sport, so you might leave it at that, or you might attach a collection of sports to a competition as well, so that you can retrieve new competitions by sport before there is a competition_instance. I'd need more details on your use case to give you further advice.
I want my route to be something like cars(/:country/):car_id, what is the best way to do that? Only "cars" will list all the cars and "cars /: country" will list all the cars that are made in that country.
Now I have my route like this resources: cars,: path => "cars (/:country)" and I check in cars#index action if params[:country] is nil to determine what will be retrieved from the database .
My solution feels wrong and ugly and I guess the best solution and cleanest would be to make a country model, but do not really know how to organize it all up, tips?
country must have a slug and so do car_id too (using friendly_id for car_id). It feels like I should have a car table with name and slug thats all i have figured out.
Thanks!
First I'd say that your current solution is NOT ugly, nor wrong, at worst it's pedestrian. But without seeing all the involved models and associations, I can only give a general answer.
First, A country model, probably a good idea, but how do you relate it to the cars model?
You could do this:
class Country << ActiveRecord::Base
has_may :cars
end
class Car << ActiveRecord::Base
belongs_to :country
end
That would support semantics where by you could select a country, and get all cars belonging to a certain country, i.e.
#cars = Country.find('USA').cars
OR, you could do something like:
class Car << ActiveRecord::Base
has_one :country
end
class Country << ActiveRecord::Base
end
That would enable a different semantic:
#country = Car.find('Jeep').country
The point is to think of the query semantics you'd like to have in your app, and then define your associations to support the semantics that make sense for your app. I've posted very simple associations, you may end up with multiple and more complex associations, just depends on how you need to query the database and the associated models.
UPDATE
You posted:
I want my route to be something like cars(/:country/):car_id,
That doesn't make sense, if you know the specific car_id, you don't need any filtering or extra searching.
Sound like you want these URLs:
/cars # all cars
/cars/:country # all cars in country
/car/:id # a specific car
The first and third routes are probably there assuming you've defined the full set of RESTful routes for cars, i.e.
config/routes.rb
resources :cars
You just need to add to routes.rb:
GET '/cars/:country' => 'cars#index'
Then in app/controllers/cars_controller.rb:
def index
if params[:country]
#cars = Car.where("country_id = ?", params[:country])
else
#cars = Car.all
end
end
This assumes you have a relationship set up whereby each car record has a country_id attribute. That can come about in several ways, for example:
class Car < ActiveRecord::Base
belongs_to :country
end
That says my car table has a country_id attribute, and I can do something like:
#car = Car.find(1001)
"The car is in #{#car.country.name}"
I have the following models:
Student has_many :subjects, :through => :classes
Subject has_many :students, :through => :classes
Class belongs_to :subject
belongs_to :student
The model class has an extra attribute (among the foreign keys to subject and students table) called level.
Basically I want to be able to have a form that will let the student to choose a subject and relate that subject to its record. So, I have this:
ClassesController < ApplicationController
def new
#list_of_subjects = Subject.all
# What should I do here?
end
My question is: How should I create the object for the form? From which model it should be, subject, student or class? I want to be able to create a record in the class table that would relate the student and the subject that the student has chosen, but I don't know if I am doing it wrong.
Thanks
I didn't think you could create a model called Class since it's a keyword, but that's neither here nor there...
First I think your controller and view should be using Student since it's the student that's selecting these things. Next, I think what you want to do is to add accepts_nested_attributes_for :class in your Student model which allows you to create an instance of the Class connector model from Student.
What you're trying to do sounds a little like something I tried to do. I have my full code there.
Using nested attributes to easily select associations in a form
I later refined it a bit in this question too to make the code less hideous:
Rails: How do I prepend or insert an association with build?
I know it's late, but I hope that helps.
Rails newbie here struggling with a small project. I am creating a simple ship building tool for a board game I like as an exercise and I am a bit lost.
What do I want to do?
-After creating my Ship model record I want to create the Traits model record that will be associated with the Ship model. After updating a Ship model record I want to update or create the Traits model that will be associated with the Ship model record.
What have I tried?
- Adding the traits to each Ship model record as column variables. I do not think that this is the most effecient way of storing the traits for each of my Ship models. I have a Traits model set up but I do not know how to navigate to it and associate it with my Ship models
What would I like to have when finished?
- An array that is stored in each Ship model record that will list the attributes for each ship with their corresponding values,
i.e. if
trait_list = [trait1 => t1, trait2 => t2, trait3 => t3, trait4 => t4]
ship_traits = [t1, t4].
In the end I would be able to call the traits on my ship diagram page without having to iterate through every single trait, just the ones pertinent to my current model.
I am lost on how I should set up the associations between the models. Any help or kind advice on directions I should be researching would be warmly welcomed. I apologize in advance for my vagueness, again I am a complete newbie.
Cheers,
Nick
I'm not 100% sure this would solve your problem, but you could do something like this:
class Ship < ActiveRecord::Base
has_many :traits
accepts_nested_attributes_for :traits
end
class Trait < ActiveRecord::Base
belongs_to :ship
end
# In your form
- form_for #ship do |f|
- f.fields_for :traits do |ff|
= ff.label :trait_name
= ff.text_field :trait_name
# this will return all the traits for model defined as #ship
#ship.traits
I know it's not an array within the Ship model, but I hear it's a little tricky to set a column in a model to be array. If you want the traits to be unique (as in many ships can have many traits and these traits can belong to many different ships), then you're going to have a has_many :through relationship. If that's the case, let me know and I'll answer again. Or you can take a look at this: http://guides.rubyonrails.org/association_basics.html
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.