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Active Record objects can be created from a hash, a block, or have their attributes manually set after creation. The new method will return a new object while create will return the object and save it to the database. A call to user. save will commit the record to the database.
They essentially do the same thing, the only difference is what side of the relationship you are on. If a User has a Profile , then in the User class you'd have has_one :profile and in the Profile class you'd have belongs_to :user . To determine who "has" the other object, look at where the foreign key is.
Active Record facilitates the creation and use of business objects whose data requires persistent storage to a database. It is an implementation of the Active Record pattern which itself is a description of an Object Relational Mapping system.
The Active Record Pattern is used to access the data stored in a relational database. It allows us to create, read, update, and delete data from a database. It is particularly used for persistently stored data.
Where it is documented:
From the API documentation under the has_many association in "Module ActiveRecord::Associations::ClassMethods"
collection.build(attributes = {}, …) Returns one or more new objects of the collection type that have been instantiated with attributes and linked to this object through a foreign key, but have not yet been saved. Note: This only works if an associated object already exists, not if it‘s nil!
The answer to building in the opposite direction is a slightly altered syntax. In your example with the dogs,
Class Dog
has_many :tags
belongs_to :person
end
Class Person
has_many :dogs
end
d = Dog.new
d.build_person(:attributes => "go", :here => "like normal")
or even
t = Tag.new
t.build_dog(:name => "Rover", :breed => "Maltese")
You can also use create_dog to have it saved instantly (much like the corresponding "create" method you can call on the collection)
How is rails smart enough? It's magic (or more accurately, I just don't know, would love to find out!)
@article = user.articles.build(:title => "MainTitle")
@article.save
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