I have two models: User and Club and I have a many-to-may relationship like:
user has_and_belongs_to_many clubs
club has_and_belongs_to_many users
Now, I will have a third table with the result of this relationship:
user_clubs(user_id, club_id)
When generating scaffold, for example, rails generate scaffold User name:string birth_date:date
gender:string login_id:integer, how can I generate that relationship? In the same way?
Thank you
You need to use generate migration
rails g migration create_club_users user_id:integer club_id:integer
It will create the following migration:
class CreateClubUsers < ActiveRecord::Migration
def change
create_table :club_users do |t|
t.integer :user_id
t.integer :club_id
end
end
end
Then you should set id to false as in Create an ActiveRecord database table with no :id column?
I suggest that you read WHY YOU DON’T NEED HAS_AND_BELONGS_TO_MANY RELATIONSHIPS.
You can try this:
rails g migration CreateClubsUsersJoinTable club_id:integer user_id:integer
You should follow alphabetical order of models when creating join table of has_and_belongs_to_many association in rails
Please refer this link for further assistance
http://apidock.com/rails/ActiveRecord/Associations/ClassMethods/has_and_belongs_to_many
Related
I have an old rails project using Rails 2 . There is already model class Student. In database, there is a table students. Now, I need to implement that each student can have multiple courses. Which means I need to have a new table in database that's courses table & have one-to-many relationship from student to course.
How to create migration file to make this?
Rails 2 didn't have an option to create associations via the migration generator, so you have to take a more manual approach.
You can create the migration thusly: https://www.tutorialspoint.com/ruby-on-rails-2.1/rails-migrations.htm
You'll need to add the column student_id to your courses table with a column type of integer
Then add the following to your Student model:
has_many :courses
This shouldn't be too difficult if you are actually using Rails 2.3
And TBH if you aren't AT LEAST on 2.3, then you should probably just recreate this project entirely...
1.) Use ruby script/generate model Course name:string description:text student_id:bigint to generate your migration, which should look something like this:
class CreateCourses < ActiveRecord::Migration
def self.up
create_table :courses do |t|
t.string :name
t.text :description
t.bigint :student_id
t.timestamps
end
end
def self.down
drop_table :courses
end
end
2.) Find the newly created MODEL in your project directory with name course and add the association to the file:
belongs_to :student
3.) Find the STUDENT model in your project folder and add the has_many association to that:
has_many :students
4.) In your terminal, cd into your project folder and run rake db:migrate
You should be good to go after that! Here's the reference for Rails 2.3 associations: https://guides.rubyonrails.org/v2.3/association_basics.html
I have looked through many SO and google posts for generating migration of join table for has many and belongs to many association and nothing work.
All of the solutions are generating a empty migration file.
I am using rails 3.2.13 and I have two tables: security_users and assignments. These are some of things I have try:
rails generate migration assignments_security_users
rails generate migration create_assignments_security_users
rails generate migration create_assignments_security_users_join_table
rails g migration create_join_table :products, :categories (following the official documentation)
rails generate migration security_users_assignments security_user:belongs_to assignments:belongs_to
Can anyone tell how to create a join table migration between two tables?
To autopopulate the create_join_table command in the command line, it should look like this:
rails g migration CreateJoinTableProductsSuppliers products suppliers
For a Product model and a Supplier model. Rails will create a table titled "products_suppliers". Note the pluralization.
(Side note that generation command can be shortened to just g)
Run this command to generate the empty migration file (it is not automatically populated, you need to populate it yourself):
rails generate migration assignments_security_users
Open up the generated migration file and add this code:
class AssignmentsSecurityUsers < ActiveRecord::Migration
def change
create_table :assignments_security_users, :id => false do |t|
t.integer :assignment_id
t.integer :security_user_id
end
end
end
Then run rake db:migrate from your terminal. I created a quiz on many_to_many relationships with a simple example that might help you.
I usually like to have the "model" file as well when I create the join table. Therefore I do.
rails g model AssignmentSecurityUser assignments_security:references user:references
There's embeded generation for join table in rails
rails g migration AddCityWorkerJoinTable cities:uniq workers
which generates following migration
create_join_table :cities, :workers do |t|
t.index [:city_id, :worker_id], unique: true
end
❗️ NOTE:
models names should go in alphabet order
put :uniq only on first param
I believe this would be an updated answer for rails 5
create_table :join_table_name do |t|
t.references :table_name, foreign_key: true
t.references :other_table_name, foreign_key: true
end
I'm wondering how I can add associations to my models. Suppose, I generate two models
rails generate model User
rails generate model Car
Now I want to add an associations so that the models acquire the form
class User < ActiveRecord::Base
has_many :cars
end
class Car < ActiveRecord::Base
belongs_to :user
end
The question is: how to apply this modification by migrations in order to obtain cars_users table in the database? I'm planning to use that table in my code.
belongs_to association expect an association_id column in its corresponding table. Since cars belongs_to user, the cars table should have a user_id column. This can be accomplished 2 ways.
first, you can generate the column when you create the model
rails g model car user_id:references
or just add the user_id after you create the model like Richard Brown's answer. Be careful that if you use integer instead of references, you'd have to create the index yourself.
rails g migration add_user_id_to_cars user_id:integer
then in the generated migration, add
add_index :cars, :user_id
UPDATE:
As Joseph has mentioned in the comments, the need to add the index manually has already been addressed in the current version of Rails. I think it was introduced in Rails 4. You can read more of it in the official Rails guide for migrations. The gist of it is running the following generator
bin/rails g migration add_user_to_cars user:references
will create a migration with a line similar to
add_reference :cars, :user, index: true
This will add a user_id column to the cars table and it will also mark that column to be indexed.
Following #jvnill's explanation in rails 4 (and maybe in rails 3.2 too) you can do it like this too (avoiding the id parts and remembering the exact convetions):
rails g migration AddUserToCar user:references
Which will create the following migration, taking care of both adding the column and index with all correct conventions:
class AddUserToCar < ActiveRecord::Migration
def change
add_reference :cars, :user, index: true
end
end
At the end as always run the migration:
rake db:migrate
View your schema.rb to view the new index and user_id column.
Generate a migration to create the association:
rails g migration AddUserIdToCars user_id:integer
rake db:migrate
Migration file:
class Createuser < ActiveRecord::Migration[5.0]
def change
create_table :users do |t|
t.string :name
end
create_table :cars do |t|
t.belongs_to :user, index: true
t.varchar(255) :model
t.varchar(255) :color
end
end
end
I've been using the tutorial by Michael Hartl and I am trying to create a new model called "Recipe" to allow users to post recipes. The model is essentially the same as the micropost model, in that a user should be able to post many recipes and all recipes should be linked to one user. I therefore used the same command and migration as for the micropost:
class CreateMicroposts < ActiveRecord::Migration
def change
create_table :microposts do |t|
t.string :content
t.integer :user_id
t.timestamps
end
add_index :microposts, [:user_id, :created_at]
end
end
Created using the command: rails generate model Micropost content:string user_id:integer
The issue I am having though is that the primary key in both tables is the user_id. Will this work, or when I go to try to enter a recipe will it try to pull from the microposts table instead? Thanks in advance
when I go to try to enter a recipe will it try to pull from the microposts table instead?
No. The Recipe model in your application by default will interact with a recipes table in your database. Similarly, a Micropost model will interact with a microposts table in your database by default.
As long as you work with the Recipe model, an instance of Recipe will not pull from the microposts table.
It sounds like you may have a fundamental misunderstanding about what a table's primary key is for, and perhaps how database tables work; but for now that's outside of the scope of this question.
As an aside, you probably should have done
rails generate model MicroPost content:string user_id:integer
(notice the uppercase P in MicroPost). This is a better name for the clase and will create a micro_posts table in your database.
The primary key is not the user_id in any of the two tables. Each model generates a table with an implicit numeric autoincremented id column that is used as the PK.
What the add_index does is add an index on the user_id column. An index is not a PK.
Anyway, you should change your add_index statement in your recipes migration to:
add_index :recipes, [:user_id, :created_at]
I have two objects i.e. recipe & ingredient.
I have created them using
rails generate scaffold ingredient id:integer name:string
rails generate scaffold recipe id:integer name:string
I want too create them with a n:m relation (many-to-many).
How do I do it? Should I create a different scaffold?
Thanks.
No, you need to create a join table, by generatin a migration.
rails g migration ingredients_recipes ingredient_id:integer recipient_id:integer
Then, you can add to your models:
Ingredient.rb
has_and_belongs_to_many :recipe
Recipe.rb
has_and_belongs_to_many :ingredients
Or if you want to add other properties to the connection (e.g. Quantity), then you may generate a model for it.
rails g model ingredients_recipes ingredient_id:integer recipient_id:integer
You can execute rails generate migration create_join_table_ingredient_recipe ingredient recipe which will generate a migrations file, which you can modify to include indices and foreign keys, like:
class CreateJoinTableIngredientRecipe < ActiveRecord::Migration
def change
create_join_table :ingredients, :recipes do |t|
t.index [:ingredient_id, :recipe_id]
t.index [:recipe_id, :ingredient_id]
end
add_foreign_key :ingredients_recipes, :ingredients
add_foreign_key :ingredients_recipes, :recipes
end
end
Then you can add in models/ingredient.rb:
has_and_belongs_to_many :recipe
and conversely in models/recipe.rb:
has_and_belongs_to_many :ingredients
Here is a great tutorial which shows two methods for using many_to_many relationships : http://railscasts.com/episodes/47-two-many-to-many