tl;dr
- Use form models to handle this problem
- Or soften the validation to
validates_presence_of :parent
Usually you would validate presence of parent object id, like in this example:
class Parent < ActiveRecord::Base
has_many :nested, :inverse_of => :parent
accepts_nested_attributes_for :nested
end
class Nested < ActiveRecord::Base
belongs_to :parent
validates_presence_of :parent_id # <-
end
With the parent already persisted creating nesteds still works fine.
But one will encounter a 'parent id missing' error on creating a parent record and a nested record at once.
To be able to create parent and nested at once one has to soften the validation to only validate on the associated object:
class Nested < ActiveRecord::Base
belongs_to :parent
validates_presence_of :parent # <- without `_id`
end
Drawback
With this softened validation now it's technically possible to create nested records without a parent id.
To make sure developers are made aware of doing somthing undesired the database could be set to throw an error on parent id columns with null values.
An odd side effect might occur in combination with scoped uniqueness validations.
Form models for more control
Using form models and so having custom control over the creation sequence it's possible to keep the validation on parent id and still be able to create parent and nested at once.
