new

Eager loads the named associations for the given Active Record record(s).

In this description, ‘association name’ shall refer to the name passed to an association creation method. For example, a model that specifies belongs_to :author, has_many :buyers has association names :author and :buyers.

Parameters

records is an array of ActiveRecord::Base. This array needs not be flat, i.e. records itself may also contain arrays of records. In any case, preload_associations will preload all associations records by flattening records.

associations specifies one or more associations that you want to preload. It may be:

• a Symbol or a String which specifies a single association name. For example, specifying :books allows this method to preload all books for an Author.

• an Array which specifies multiple association names. This array is processed recursively. For example, specifying [:avatar, :books] allows this method to preload an author’s avatar as well as all of his books.

• a Hash which specifies multiple association names, as well as association names for the to-be-preloaded association objects. For example, specifying { author: :avatar } will preload a book’s author, as well as that author’s avatar.

:associations has the same format as the :include method in ActiveRecord::QueryMethods. So associations could look like this:

:books
[ :books, :author ]
{ author: :avatar }
[ :books, { author: :avatar } ]

available_records is an array of ActiveRecord::Base. The Preloader will try to use the objects in this array to preload the requested associations before querying the database. This can save database queries by reusing in-memory objects. The optimization is only applied to single associations (i.e. :belongs_to, :has_one) with no scopes.