Add Nullable Foreign Key in Rails

Add nullable foreign key in Rails

There is nothing in the guide that implies add_foreign_key would make the corresponding foreign field "NOT NULL" or required. add_foreign_key simply adds a foreign key constraint whether the field is required or not (in your case author_id in articles).

Did you get an error when you tried this in your migration?

Here's the SQL that it would generate:

ALTER TABLE "articles" ADD CONSTRAINT articles_author_id_fk FOREIGN KEY ("author_id") REFERENCES "authors" ("id")

SO, if in your original migration of articles, author_id is null, then you can have foreign key that's nullable.

Ruby on rails - set up a null foreign key

It's allowed to be null on db level. Within Time models add optional option, like - belongs_to :user, optional: true
Check related docs here

rails 6 foreign key can't be null

Migrations are not a declaration of current db structure, they are changes that when combined - produce it. For combined structure rails have db/schema.rb (or schema.sql for more complex scenarios)

If the column is null: false then it must have been changed by some later migration (or directly in db, if so - db structure may be out of sync between development and production). If you want it again to be null: true - add another migration that will change that. But first I'd figure out why it ended up in current state, may be there's a reason.

change_column :carts, :user_id, :bigint, null:true

Foreign key is allowed to be NULL?

For add foreign key, you add first the name of table (not the model name), this as first parameter, and as second parameter the name of foreign table(not the model name).
The table as first parameter should have a column with a name specific as follow: name_foreign_model_id.
Example:
Foreign model

class CreateGrades < ActiveRecord::Migration
  def change
    create_table :grades do |t|
      t.string :name, limit: 20
      t.integer :level, limit: 2
      t.string :next, limit: 20

      t.timestamps null: false
    end
  end
end

And,

class CreateGoals < ActiveRecord::Migration
  def change
    create_table :goals do |t|
      t.integer :dimension, limit: 2, null: false
    **t.integer :grade_id, null: false**
      t.string :description, limit: 1024, null: false

      t.timestamps null: false
    end
    **add_foreign_key :goals, :grades**
  end
end

Also you can add foreign key in a separate migration.

With this, not should accept null foreign key.

Ruby on Rails foreign key field cannot be null

You can make the assignments conditional on whether there's already a value...

  before_validation do
    self.banned = false if banned.nil?
    self.role ||= Role.find_by(title: 'User')
  end

Or you can do it only on create....

  before_validation do
    if new_record?
      self.banned = false
      self.role = Role.find_by(title: 'User')
    end
  end

But frankly the way I normally see initial defaults set is in the create method of the controller

def create
  @user = User.assign_attributes(user_params)
  @user.banned = false
  @user.role = Role.find_by(title: 'User')
  if @user.save
    # ...

Rails foreign key optional don't work

You don't need foreign_key: true on the t.refrences lines. They'll force referential integrity tests.

Roll back, then change the migration to...

t.references :deck
t.references :game

Alternatively you can just create the integer fields and bypass the database integrieites

t.integer :deck_id
t.integer :game_id

User_ID foreign key NULL in Rails

Not sure , may be because you didn't run it properly. Please recheck all this below conditions.

1. user_id must be in website table . To add migration you should run rails g migration AddUserIdToZombies user_id:integer and then rake db:migrate
2. To ensure the user_id must be there with websites table,put validation.
3. To assign user_id automatically,you should do something like u = User.find 1 u.websites.create(attr: 'value')

FYI :Rails dont use foreign key concept. It means that they dont put link in database. They just provide abstract way of linking models.

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