Set this to true if this is an abstract class (see abstract_class?). If you are using inheritance with Active Record and don't want a class to be considered as part of the STI hierarchy, you must set this to true. ApplicationRecord, for example, is generated as an abstract class.
Consider the following default behaviour:
Shape = Class.new(ActiveRecord::Base) Polygon = Class.new(Shape) Square = Class.new(Polygon) Shape.table_name # => "shapes" Polygon.table_name # => "shapes" Square.table_name # => "shapes" Shape.create! # => #<Shape id: 1, type: nil> Polygon.create! # => #<Polygon id: 2, type: "Polygon"> Square.create! # => #<Square id: 3, type: "Square">
However, when using abstract_class, Shape is omitted from the hierarchy:
class Shape < ActiveRecord::Base self.abstract_class = true end Polygon = Class.new(Shape) Square = Class.new(Polygon) Shape.table_name # => nil Polygon.table_name # => "polygons" Square.table_name # => "polygons" Shape.create! # => NotImplementedError: Shape is an abstract class and cannot be instantiated. Polygon.create! # => #<Polygon id: 1, type: nil> Square.create! # => #<Square id: 2, type: "Square">
Note that in the above example, to disallow the creation of a plain Polygon, you should use validates :type, presence: true, instead of setting it as an abstract class. This way, Polygon will stay in the hierarchy, and Active Record will continue to correctly derive the table name.
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 activerecord/lib/active_record/inheritance.rb, line 156 def abstract_class? defined?(@abstract_class) && @abstract_class == true end
Returns whether this class is an abstract class or not.
# File activerecord/lib/active_record/inheritance.rb, line 108 def base_class? base_class == self end
Returns whether the class is a base class. See base_class for more information.
# File activerecord/lib/active_record/inheritance.rb, line 81
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 Returns true if this does not need STI type condition. Returns false if STI type condition needs to be applied.
# File activerecord/lib/active_record/inheritance.rb, line 213 def inherited(subclass) subclass.set_base_class subclass.instance_variable_set(:@_type_candidates_cache, Concurrent::Map.new) super end
# File activerecord/lib/active_record/inheritance.rb, line 55
def new(attributes = nil, &block)
if abstract_class? || self == Base
raise NotImplementedError, "#{self} is an abstract class and cannot be instantiated."
end
if _has_attribute?(inheritance_column)
subclass = subclass_from_attributes(attributes)
if subclass.nil? && scope_attributes = current_scope&.scope_for_create
subclass = subclass_from_attributes(scope_attributes)
end
if subclass.nil? && base_class?
subclass = subclass_from_attributes(column_defaults)
end
end
if subclass && subclass != self
subclass.new(attributes, &block)
else
super
end
end 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.
# File activerecord/lib/active_record/inheritance.rb, line 205
def polymorphic_class_for(name)
if store_full_class_name
name.constantize
else
compute_type(name)
end
end Returns the class for the provided name.
It is used to find the class correspondent to the value stored in the polymorphic type column.
# File activerecord/lib/active_record/inheritance.rb, line 198 def polymorphic_name store_full_class_name ? base_class.name : base_class.name.demodulize end
Returns the value to be stored in the polymorphic type column for Polymorphic Associations.
# File activerecord/lib/active_record/inheritance.rb, line 166
def primary_abstract_class
if ActiveRecord.application_record_class && ActiveRecord.application_record_class.name != name
raise ArgumentError, "The `primary_abstract_class` is already set to #{ActiveRecord.application_record_class.inspect}. There can only be one `primary_abstract_class` in an application."
end
self.abstract_class = true
ActiveRecord.application_record_class = self
end Sets the application record class for Active Record
This is useful if your application uses a different class than ApplicationRecord for your primary abstract class. This class will share a database connection with Active Record. It is the class that connects to your primary database.
# File activerecord/lib/active_record/inheritance.rb, line 183
def sti_class_for(type_name)
if store_full_sti_class && store_full_class_name
type_name.constantize
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 Returns the class for the provided type_name.
It is used to find the class correspondent to the value stored in the inheritance column.
# File activerecord/lib/active_record/inheritance.rb, line 176 def sti_name store_full_sti_class && store_full_class_name ? name : name.demodulize end
Returns the value to be stored in the inheritance column for STI.
# File activerecord/lib/active_record/inheritance.rb, line 235
def compute_type(type_name)
if type_name.start_with?("::")
# If the type is prefixed with a scope operator then we assume that
# the type_name is an absolute reference.
type_name.constantize
else
type_candidate = @_type_candidates_cache[type_name]
if type_candidate && type_constant = type_candidate.safe_constantize
return type_constant
end
# Build a list of candidates to search for
candidates = []
name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" }
candidates << type_name
candidates.each do |candidate|
constant = candidate.safe_constantize
if candidate == constant.to_s
@_type_candidates_cache[type_name] = candidate
return constant
end
end
raise NameError.new("uninitialized constant #{candidates.first}", candidates.first)
end
end 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.
© 2004–2021 David Heinemeier Hansson
Licensed under the MIT License.