I have two models, Staff and Hospital, in a belongs_to has_many relationship. A hospital has many staff. My staff table look like this:
class CreateStaffs < ActiveRecord::Migration[5.1]
def change
create_table :staffs do |t|
t.string :Title
t.string :FirstName
.
.
.
t.integer :hospital_id
t.timestamps
end
end
end
Can't I specify a different foreign key, such as hospital_name?
Thanks
What you need is to create the table like this:
create_table :staffs do |t|
...
t.string :hospital_name
end
add_foreign_key :staffs, :hospitals, column: :hospital_name, primary_key: :name
where with primary_key: :name you reference the column name of the hospitals table.
Related
Please how can I reference a table when not using the default table id as the table's primary key? I created two tables one having email as the primary key and I want to have this table email as the foreign key in the other table. Please How can i achieve that?
You may create table with email as primary key like this:
create_table :users, id: false do |t|
t.string :email, primary_key: true
t.string :name
t.timestamps
end
create_table :posts do |t|
t.string :title
t.text :body
t.string :user_email
t.timestamps
end
And define your models like this:
class User < ActiveRecord::Base
self.primary_key = 'email'
has_many :posts, foreign_key: :user_email
end
class Post < ActiveRecord::Base
belongs_to :user, foreign_key: :user_email
end
That's all you need to do. Also you may keep id as primary key for User model but use use email as foreign key - this may be easier way to handle your models.
Hello i have to model like;
class CreateLecturers < ActiveRecord::Migration
def change
create_table :lecturers do |t|
t.string :firstname
t.string :lastname
t.string :position
t.string :email
t.timestamps null: false
end
end
end
and here is my second model.
class CreateCurriculums < ActiveRecord::Migration
def change
create_table :curriculums do |t|
t.string :title
t.integer :hours
t.integer :year
t.text :description
t.timestamps null: false
end
end
end
I want migrate to Curriculums to Lecturer. But not with id, with title
how it's can be possible?
So i use rails-admin. When i add some Curriculum i want to choose with dropdown lecturer and when i add some Lecturer i want to choose Curriculum between models .
No matter what, you have to have association between two models. Also do not forget to add curriculum_id to lectures table.
curriculum.rb
has_many :lectures
lecture.rb
belongs_to :curriculum
To add migration
rails g migration add_curriculum_id_to_lectures curriculum_id:integer
I have a Rails project with postgresql database.
Let's say I have three models - Student, Teacher and Schedule - that joins a student and teacher
Student Model - Instead of going with the student_id as my primary key, I want to change that to the even_cooler_unique_student_number that a school has for a student.
Teacher Model - typical & traditional.
Schedule Model - I want to associate a Schedule (think - just a math class for now) with one teacher and its students.
How do I do that at the database level and with the AR associations?
What does changing the primary_key do to the database? To my associations through ActiveRecord?
class CreateStudent < ActiveRecord::Migration
def change
create_table :students do |t|
t.integer :unique_cooler_student_id, null: false
t.string :first_name
t.string :last_name
t.timestamps null: false
end
end
end
class CreateTeacher < ActiveRecord::Migration
def change
create_table :teachers do |t|
t.string :first_name
t.string :last_name
t.string :department
t.timestamps null: false
end
end
end
class CreateSchedules < ActiveRecord::Migration
def change
create_table :schedules, id: false, force: true do |t|
t.belongs_to :students, :primary_key => 'unique_cooler_student_id'
t.belongs_to :teachers
t.string :something_else
t.timestamps null: false
end
end
end
class Student
self.primary_key = 'unique_cooler_student_id'
has_many :teachers, through: :classes
end
class Teacher
has_many :students, through: :classes
end
class Schedule
belongs_to :students
belongs_to :teachers
end
Changing the name of primary key usually does very little besides adding a false sense of security - which is only by obscurity.
You can however change the primary key from a auto-incrementing integer to a hash or some other sort of UUID. And there are many valid reasons to do so. This solely changes the method of generating primary keys.
You can even have separate external UUIDs which are used in url params for example. However this does not involve changing the primary key that ActiveRecord uses to join records:
Foo.joins(:bars).find_by(uuid: 'ABCD')
Of course ActiveRecord will let you crack out the tin-foil hat and use whatever primary keys you want - however you will need to specify the primary_key and probably also manually setup the foreign keys in your database to maintain referential integrity. So basically your losing every advantage of convention over configuration for no benefit.
You would have to do it like this:
class CreateSchedules < ActiveRecord::Migration
def change
create_table :schedules, id: false, force: true do |t|
t.references :students, foreign_key: false
t.belongs_to :teachers
t.string :something_else
t.timestamps null: false
end
end
end
class AddStudensIdContraintToSchedules < ActiveRecord::Migration
def change
add_foreign_key :schedules, :students, primary_key: "unique_cooler_student_id"
end
end
class Schedule
has_many :students, primary_key: 'unique_cooler_student_id'
end
This way AR uses WHERE students.unique_cooler_student_id = 2 in the join query.
The only reason you would ever really want to do this this is if you have to use a legacy database and cannot change the database schema.
I have this table structure:
class CreateUsers < ActiveRecord::Migration
def change
create_table :users do |t|
t.string :username
t.string :email
t.string :encrypted_password
t.string :salt
t.timestamps
end
end
end
And I want to add a new table as shown below:
class CreateHolidays < ActiveRecord::Migration
def change
create_table :holidays do |t|
t.string :earn_leave
t.string :seek_leave
t.string :unplanned_leave
t.timestamps
t.timestamps
end
add_index(users,id)
end
end
What should I do for this, please also suggest commands that can/should be used for migration.
You want to look up about foreign_keys:
#app/models/holiday.rb
class Holiday < ActiveRecord::Base
belongs_to :user
end
#app/models/user.rb
class User < ActiveRecord::Base
has_many :holidays
end
This will mean you have to add the user_id foreign key to your holidays data table:
class CreateHolidays < ActiveRecord::Migration
def change
create_table :holidays do |t|
t.references :user
t.string :earn_leave
t.string :seek_leave
t.string :unplanned_leave
t.timestamps
t.timestamps
end
end
end
You must remember that Rails is designed to be built on top of a relational database. As such, it uses foreign_keys in the tables to locate associated records:
The above will allow you to call:
#user.holidays
and
#holiday.user
In my web app, I have nodes and links. A link has two nodes. One node is a source node, and the other node is a target node. Basically, I want source and target columns in the database that hold references to nodes. I am trying to figure out how to implement this.
Here is the migration for the nodes model:
class CreateNodes < ActiveRecord::Migration
def change
create_table :nodes do |t|
t.string :name
t.integer :group
t.references :link, index: true
t.timestamps
end
end
end
Here is the node model:
class Nodes < ActiveRecord::Base
belongs_to :link
end
I am trying to figure out how to set up the migration for the links model. Here is what I have so far:
class CreateLinks < ActiveRecord::Migration
def change
create_table :links do |t|
t.integer :value
t.boolean :checked
t.timestamps
end
end
end
Here is what I have in my model:
class Links < ActiveRecord::Base
has_many :nodes
end
Would the correct migration look like this?
class CreateLinks < ActiveRecord::Migration
def change
create_table :links do |t|
t.integer :value
t.boolean :checked
t.references :source
t. references :target
t.timestamps
end
end
end
t.references :smith is basically a shortcut for t.integer :smth_id so if your Nodes belong to Links, then yes that construction seems correct.
not sure where your links#source and links#target point to though.