# File activerecord/lib/active_record/persistence.rb, line 29
def create(attributes = nil, &block)
  if attributes.is_a?(Array)
    attributes.collect { |attr| create(attr, &block) }
  else
    object = new(attributes, &block)
    object.save
    object
  end
end

Creates an object (or multiple objects) and saves it to the database, if validations pass. The resulting object is returned whether the object was saved successfully to the database or not.

The attributes parameter can be either a Hash or an Array of Hashes. These Hashes describe the attributes on the objects that are to be created.

Examples

# Create a single new object
User.create(first_name: 'Jamie')

# Create an Array of new objects
User.create([{ first_name: 'Jamie' }, { first_name: 'Jeremy' }])

# Create a single object and pass it into a block to set other attributes.
User.create(first_name: 'Jamie') do |u|
  u.is_admin = false
end

# Creating an Array of new objects using a block, where the block is executed for each object:
User.create([{ first_name: 'Jamie' }, { first_name: 'Jeremy' }]) do |u|
  u.is_admin = false
end

# File activerecord/lib/active_record/persistence.rb, line 46
def create!(attributes = nil, &block)
  if attributes.is_a?(Array)
    attributes.collect { |attr| create!(attr, &block) }
  else
    object = new(attributes, &block)
    object.save!
    object
  end
end

Creates an object (or multiple objects) and saves it to the database, if validations pass. Raises a RecordInvalid error if validations fail, unlike Base#create.

The attributes parameter can be either a Hash or an Array of Hashes. These describe which attributes to be created on the object, or multiple objects when given an Array of Hashes.

# File activerecord/lib/active_record/persistence.rb, line 66
def instantiate(attributes, column_types = {}, &block)
  klass = discriminate_class_for_record(attributes)
  attributes = klass.attributes_builder.build_from_database(attributes, column_types)
  klass.allocate.init_with("attributes" => attributes, "new_record" => false, &block)
end

Given an attributes hash, instantiate returns a new instance of the appropriate class. Accepts only keys as strings.

For example, Post.all may return Comments, Messages, and Emails by storing the record's subclass in a type attribute. By calling instantiate instead of new, finder methods ensure they get new instances of the appropriate class for each record.

See ActiveRecord::Inheritance#discriminate_class_for_record to see how this “single-table” inheritance mapping is implemented.