module ActiveRecord::Inheritance::ClassMethods

Attributes

abstract_class[RW]

Set this to true if this is an abstract class (see abstract_class?). If you are using inheritance with ActiveRecord and don't want child classes to utilize the implied STI table name of the parent class, this will need to be true. For example, given the following:

class SuperClass < ActiveRecord::Base
  self.abstract_class = true
end
class Child < SuperClass
  self.table_name = 'the_table_i_really_want'
end

self.abstract_class = true is required to make Child<.find,.create, or any Arel method> use the_table_i_really_want instead of a table called super_classes

Public Instance Methods

abstract_class?() click to toggle source

Returns whether this class is an abstract class or not.

# File lib/active_record/inheritance.rb, line 124
def abstract_class?
  defined?(@abstract_class) && @abstract_class == true
end
base_class() click to toggle source

Returns the class descending directly from ActiveRecord::Base, or an abstract class, if any, in the inheritance hierarchy.

If A extends ActiveRecord::Base, A.base_class will return A. If B descends from A through some arbitrarily deep hierarchy, B.base_class will return A.

If B < A and C < B and if A is an #abstract_class then both B.base_class and C.base_class would return B as the answer since A is an abstract_class.

# File lib/active_record/inheritance.rb, line 94
def base_class
  unless self < Base
    raise ActiveRecordError, "#{name} doesn't belong in a hierarchy descending from ActiveRecord"
  end

  if superclass == Base || superclass.abstract_class?
    self
  else
    superclass.base_class
  end
end
descends_from_active_record?() click to toggle source

Returns true if this does not need STI type condition. Returns false if STI type condition needs to be applied.

# File lib/active_record/inheritance.rb, line 71
def descends_from_active_record?
  if self == Base
    false
  elsif superclass.abstract_class?
    superclass.descends_from_active_record?
  else
    superclass == Base || !columns_hash.include?(inheritance_column)
  end
end
new(*args, &block) click to toggle source

Determines if one of the attributes passed in is the inheritance column, and if the inheritance column is attr accessible, it initializes an instance of the given subclass instead of the base class.

Calls superclass method
# File lib/active_record/inheritance.rb, line 48
def new(*args, &block)
  if abstract_class? || self == Base
    raise NotImplementedError, "#{self} is an abstract class and cannot be instantiated."
  end

  attrs = args.first
  if has_attribute?(inheritance_column)
    subclass = subclass_from_attributes(attrs)

    if subclass.nil? && base_class == self
      subclass = subclass_from_attributes(column_defaults)
    end
  end

  if subclass && subclass != self
    subclass.new(*args, &block)
  else
    super
  end
end
sti_name() click to toggle source
# File lib/active_record/inheritance.rb, line 128
def sti_name
  store_full_sti_class ? name : name.demodulize
end

Protected Instance Methods

compute_type(type_name) click to toggle source

Returns the class type of the record using the current module as a prefix. So descendants of MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.

# File lib/active_record/inheritance.rb, line 136
def compute_type(type_name)
  if type_name.match(/^::/)
    # If the type is prefixed with a scope operator then we assume that
    # the type_name is an absolute reference.
    ActiveSupport::Dependencies.constantize(type_name)
  else
    # Build a list of candidates to search for
    candidates = []
    name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" }
    candidates << type_name

    candidates.each do |candidate|
      constant = ActiveSupport::Dependencies.safe_constantize(candidate)
      return constant if candidate == constant.to_s
    end

    raise NameError.new("uninitialized constant #{candidates.first}", candidates.first)
  end
end

Private Instance Methods

discriminate_class_for_record(record) click to toggle source

Called by instantiate to decide which class to use for a new record instance. For single-table inheritance, we check the record for a type column and return the corresponding class.

Calls superclass method
# File lib/active_record/inheritance.rb, line 161
def discriminate_class_for_record(record)
  if using_single_table_inheritance?(record)
    find_sti_class(record[inheritance_column])
  else
    super
  end
end
find_sti_class(type_name) click to toggle source
# File lib/active_record/inheritance.rb, line 173
def find_sti_class(type_name)
  type_name = base_class.type_for_attribute(inheritance_column).cast(type_name)
  subclass = begin
    if store_full_sti_class
      ActiveSupport::Dependencies.constantize(type_name)
    else
      compute_type(type_name)
    end
  rescue NameError
    raise SubclassNotFound,
      "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. "              "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. "              "Please rename this column if you didn't intend it to be used for storing the inheritance class "              "or overwrite #{name}.inheritance_column to use another column for that information."
  end
  unless subclass == self || descendants.include?(subclass)
    raise SubclassNotFound, "Invalid single-table inheritance type: #{subclass.name} is not a subclass of #{name}"
  end
  subclass
end
subclass_from_attributes(attrs) click to toggle source

Detect the subclass from the inheritance column of attrs. If the inheritance column value is not self or a valid subclass, raises ActiveRecord::SubclassNotFound

# File lib/active_record/inheritance.rb, line 203
def subclass_from_attributes(attrs)
  attrs = attrs.to_h if attrs.respond_to?(:permitted?)
  if attrs.is_a?(Hash)
    subclass_name = attrs.with_indifferent_access[inheritance_column]

    if subclass_name.present?
      find_sti_class(subclass_name)
    end
  end
end
type_condition(table = arel_table) click to toggle source
# File lib/active_record/inheritance.rb, line 194
def type_condition(table = arel_table)
  sti_column = arel_attribute(inheritance_column, table)
  sti_names  = ([self] + descendants).map(&:sti_name)

  sti_column.in(sti_names)
end
using_single_table_inheritance?(record) click to toggle source
# File lib/active_record/inheritance.rb, line 169
def using_single_table_inheritance?(record)
  record[inheritance_column].present? && has_attribute?(inheritance_column)
end