I am trying to make Rails-based application (and I'm just learning RoR as I go) and I stumbled upon this problem.
There are two models: Recipe and Item (food items). Recipe can have zero (we can create recipe before adding items) or many items. But a specific food item should not be bound to any recipe. That is why 'has_many' and 'belongs_to' won't work for me, as the latter does not fill this requirement.
If I was to do this without any framework, I would probably put an 'items' column in Recipe table, which would contain a list of item indices. But I have a hunch that this is not an appropriate way to do this in RoR since there are model associations in Rails.
Please, could someone give me an idea how to go about this?
I normally don't use has_and_belongs_to_many, but in your case it seems it might fit. You can use it like this:
class Recipe
has_and_belongs_to_many :items
end
class Item
has_and_belongs_to_many :recipes
end
You can also use has_many :through, but you would have to create a third table to join the Recipe and Item tables together.
class Recipe
has_many :item_recipes
has_many :items, through: :item_recipes
end
class ItemRecipes
belongs_to :recipe
belongs_to :item
end
class Item
has_many :item_recipes
has_many :recipes, through: :item_recipes
end
You can find more information here: Rails Associations
Related
I have a user and project model created in Rails. I have to perform an association that will create an relationship which is described below:
1 User has many Projects
1 project has many Users
How can I go about creating an association for the same in Rails? I need some help on which type of association in rails will help me to achieve this.
You are describing a many-to-many relationship type. Rails allows you to create this relationship using has_many :through and has_and_belongs_to_many directives. You can learn the difference here.
Shortly, has_many :through allows you to add additional columns into the intermediate table, has_and_belongs_to_many doesn't. If you don't need to have additional attributes in the intermediate table than use has_and_belongs_to_many syntax. You can always change to has_many :through later.
class Project < ActiveRecord::Base
has_and_belongs_to_many :users
end
class User < ActiveRecord::Base
has_and_belongs_to_many :projects
end
You are basically trying to have a many-to-many relationship.
In Rails you can do this based on two association concept:
has_and_belongs_to_many (HABTM)
has_many :through
Note:
You should have HABTM if you just do not care about the way these two tables are joined (relationship model) and you do not want to have any logic/validation for your join data. It will just keep your foreign keys in a table and based on that data will be fetched.
You need has_many :through if you want to have an intermediate model in between Project and User which can be called as UserProject model. This way your association could look like as follows:
User Model:
has_many :user_projects
has_many :projects, through: :user_projects
Project Model:
has_many :user_projects
has_many :users, through: :user_projects
UserProject Model:
belongs_to :user
belongs_to :project
You can use has_and_belongs_to_many or has_many through.Here is the link I am providing which will help you to sort out difference between them and which one will be good for you.Here is the video tutorial for you association.ALso there is a good link link.In your case you need has and belongs to many
The best thing to do in this situation is ,
In your user.rb model file:
has_and_belongs_to_many :projects
and In your project.rb model file:
has_and_belongs_to_many :users
You may want too use many to many relationship between project and user. on top of that you may want to visit rails official guide which describes all of these relations in great detail.
http://guides.rubyonrails.org/association_basics.html
I'm fairly new to rails and ActiveRecord and I'm trying to find the correct way to model my data.
I am building an application that let's swim instructors put together a class plan that shows what skills they will be teaching their class and what activities they will use to teach each skill. A Plan can contain many Skills and each Skill can have many Activities associated with it.
On the Plan form there is a widget for the skill-activity combination. In it, user should be able to select a Skill from a dropdown and for the selected skill select multiple activities from a list. This widget can repeat any number of times on the form.
My current model:
Class Plan
has_many :plan_activities
end
Class PlanActivities
belongs_to :plan
belongs_to :skill
has_and_belongs_to_many :activities
end
Class Skill
end
Class Activity
end
Is this model correct? My problem with it is that accepts_nested_attribtues_for does not work for HABTM associations. I've read that I can replace it with has_many through:, but that would mean adding yet another join model to the picture. It just seems a little too ugly. Is there a better way to do this?
EDIT:
My Skills and Activities are in list form and I should be able to include the same skill and/or activity on multiple plans.
Your model is very close. One improvement here would be to completely remove the PlanActivities model. Just have the associations directly on the plan. At this point I don't think the extra model is justified. We have a pretty basic pyramid structure here. At the top is plan with many skills, Each skill has many activities, so a simpler model would look like:
class Plan
has_many :plan_skills
has_many :activities, through: :plan_skills
end
class Skill
has_many :activities, through: plan_skills
has_many :plan_skills
end
class PlanSkill
belongs_to :plan
belongs_to :skill
has_many :activities
end
class Activity
belongs_to :plan_skill
end
The join model is an option but not entirely necessary here. Plan.activities will make the needed join table for you.
I have a Rails app using Postgres and Active Record, and can't fathom the most efficient Associations between my models.
I have a Model called Article. Article needs to have a Format and 2/3 Genres.
I need articles to be able to be listed by format i.e. http://myapp.com/format/format-id/article-id
I also need articles to be listed by genre, so: myapp.com/genre/genre-name/article-id
I was thinking the Genres and Formats would be models themselves with has_many_and_belongs_to associations to Articles. Each article has multiple Genres, and 1 format, but each Genre has multiple articles.
I know this should be simple, but I can't find the most efficient route of making this happen.
There's an old Railscasts episode that goes through the two ways to do many-to-many associations with Rails - you should watch it: http://railscasts.com/episodes/47-two-many-to-many. It's old but mostly still relevant.
So, you've got Articles, Formats, and Genres. Since each Article will have only one Format, you don't need a has_and_belongs_to_many relationship there. Article belongs_to Format, and Format has_many articles.
Each row in the articles table will have a format_id field to indicate which Format it belongs to.
The relationship between Genres and Articles is a many-to-many, which is a bit trickier. At the database level, this requires a 'join table'. Your join table would be called something like articles_genres, and each row represents one genre that one particular article has. So, it'd have a genre_id column, and an article_id column.
In terms of rails, there are two ways to do this:
Give the articles_genres table it's own model. In this case you might want to also give the table a different name, to indicate it's a Model in it's own right, not just a join table. You could call it something like genreizations
or
Don't give articles_genres table it's own model, and let rails handle it all.
I generally prefer the first way - I feel more in control, and it leaves things more flexible for future. But, either will work. The railscasts episode I linked to describes both ways.
If you go the first way, this is what models you'll have:
class Article < ActiveRecord::Base
has_many :genreizations
has_many :genres, through: :genreizations
belongs_to :format
end
class Format < ActiveRecord::Base
has_many :articles
end
class Genreization < ActiveRecord::Base
belongs_to :article
belongs_to :genre
end
class Genre < ActiveRecord::Base
has_many :genreizations
has_many :articles, through: :genreizations
end
And in the second way, this is what models you'll have:
class Article < ActiveRecord::Base
has_and_belongs_to_many :genres
belongs_to :format
end
class Format < ActiveRecord::Base
has_many :articles
end
class Genre < ActiveRecord::Base
has_and_belongs_to_many :articles
end
I am new to rails and have a very basic question.
While creating models, for ex. I have to store recipe and its steps. Now should i make recipe table, steps table and recipe_steps table or should i have recipe , steps table and in the model for recipe define has_many :steps?
Any help would be great.
Thanks a lot
You always need to have 3 tables in your database. As you said recipes steps and recipe_steps
Then you have two solutions with your models. The first one with 3 models:
class Recipe
has_many :recipe_steps
has_many :steps, through: :recipe_steps
end
class Step
has_many :recipe_steps
has_many :recipes, through: :recipe_steps
end
class RecipeStep
belongs_to :step
belongs_to :recipe
end
The second one with only two models:
class Recipe
has_and_belongs_to_many :steps
end
class Step
has_and_belongs_to_many :recipes
end
You will use the second solution if you don't want to manage data in the recipe_steps table. But if you want to add some informations in this table (price or quantity for example), you must use the first solution.
In all cases you must create the 3 tables.
You will find more information here: http://guides.rubyonrails.org/association_basics.html
I hope this help
Say I have two models, Book and Author with a has_and_belongs_to_many relationship between them.
What I want to do is to be able to add author names in the book form, and on submit to either link the authors with the book if they already exist, or create them if they don't.
I also want to do the same with the author form: add book names and on submit either link them if they exist, or create them if they don't.
On edit, however, I want to neither be able to edit nor delete the nested objects, only remove the associations.
Is accepts_nested_attributes_for suitable for this, or is there another way?
I managed to accomplish this by following the Complex Forms railscasts on Rails 2, but I'm looking for a more elegant solution for Rails 3.
I'm not sure why so many people use has_and_belongs_to_many, which is a relic from Rails 1, instead of using has_many ..., :through except that it's probably in a lot of old reference books and tutorials. The big difference between the two approaches is the first uses a compound key to identify them, the second a first-class model.
If you redefine your relationship, you can manage on the intermediate model level. For instance, you can add and remove BookAuthor records instead of has_and_belongs_to_many links which are notoriously difficult to tweak on an individual basis.
You can create a simple model:
class BookAuthor < ActiveRecord::Base
belongs_to :book
belongs_to :author
end
Each of your other models is now more easily linked:
class Book < ActiveRecord::Base
has_many :book_authors
has_many :authors, :through => :book_authors
end
class Author < ActiveRecord::Base
has_many :book_authors
has_many :books, :through => :book_authors
end
On your nested form, manage the book_authors relationship directly, adding and removing those as required.