Rails 5 belongs_to weird behaviour - ruby-on-rails

Question

Client Class
class Client < ApplicationRecord
validates_presence_of :name, :email
validates_email_format_of :email, :message => 'is not looking good'
validates_uniqueness_of :email
has_many :projects
end
Project Class
class Project < ApplicationRecord
belongs_to :client, optional: false
validates_presence_of :name
end
And schema of my tables
create_table "clients", force: :cascade do |t|
t.string "name"
t.string "email"
t.string "phone"
t.string "address"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "projects", force: :cascade do |t|
t.string "name"
t.integer "client_id"
t.string "description"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
Sometime I want to create Project without having client specified. So I added option :option false. And so now I'm able to create project without specifying any client id. However when I try to create project with client_id, it accepts any value for client_id i.e. if enter 8 and if this id is not present in client then also its accepted. I want in such cases it shouldn't save this project.
How can I achieve this behaviour?
I have rails version 5.1.4

Answer 1

First some changes, is optional: true, optional: false is the default behavior and expects to get a associated record every time, with that said, you could do something like this:
class Project < ApplicationRecord
belongs_to :client, optional: true
# Sorry, small bug, client_id? with value zero would return always false and it becomes zero when you input strings or false
# validates_presence_of :client, if: client_id?
validates_presence_of :client, unless: Proc.new{ |d| d.client_id.blank? }
end
This would validate the client record when the client_id is present
p = Project.new # => #<Project id: nil, client_id: nil, ...
p.valid? # => true
p.client = Client.first # => #Client id: 1, ...
p.valid? # => true
p.client = nil # => nil
p.valid? # => true
#Non-existent id 10
p.client_id = 10 # => 10
p.valid? # => false
p.errors.full_messages # => ["Client can't be blank"]
p.client_id = 1 # => 1
p.client # => #Client id: 1, ...
p.valid? # => true
You can even use a custom message
validates_presence_of :client, message: 'invalid client', if: :client_id?
Finally, just a recommendation, use t.references on your migrations to be able to use foreign keys and get this fields indexed
t.references :client, foreign_key: true

Answer 2

I would write your own custom validation to ensure that the id of the client actually exists in your database before persisting the project record:
class Project < ApplicationRecord
belongs_to :client, optional: false
validates_presence_of :name
validate :validate_client_id, if: :client_id?
private
def validate_client_id
errors.add(:client_id, "is invalid") unless Client.exists?(self.client_id)
end
end
The validation will only run if the field is not blank. Which is convenient since client_id is optional in your case.