Time for action — modeling the Author class

First let's write the Author model. We do it as follows: 

class Author
include Mongoid::Document
field :name, type: String
validates_presence_of :name
has_one :address, as: :location, autosave: true, dependent: :destroy
has_many :books, autosave: true, dependent: :destroy
accepts_nested_attributes_for :books, :address, allow_destroy: true
end

What just happened?

An author has many books and has one address. This is declared as follows:

class Author
...
has_many :books, autosave: true, dependent: :destroy
has_one :address, as: :location, autosave: true, dependent: :destroy

...
end

Tip

We have already seen relationships via Mongoid, but here are a few more options:

  • :autosave: This option is specified in the parent model and enables its associated child objects to be saved along with the parent
  • :as: This is the polymorphic relation
  • :dependent: This option is also specified on the parent model and ensures that the dependent child objects are destroyed when the parent is destroyed

When we are creating an author, we would also like to update all the books written by the author as well as update his address. We do this by accepting nested attributes: 

class Author
...
accepts_nested_attributes_for :books, :address, allow_destroy: true

...
end

As the name suggests, accepts_nested_attributes_for accepts nested attributes for the child relation.

Tip

We can only accept nested attributes for children. That means we should use them only in the parent relation.

We shall see how this comes into play when we build the Views.

Update the Author model as follows:

class Author
...
validates_presence_of :name

...
end

Because this is a Mongoid document, it has all the features that are available with ActiveModel, such as ActiveModel::Validations. So we can use all the available validations here. In this case, we validate the presence of the name to ensure that an Author object is not created without the name!

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