module ActiveRecord::AttributeMethods::ClassMethods

# File activerecord/lib/active_record/attribute_methods.rb, line 142
def attribute_method?(attribute)
  super || (table_exists? && column_names.include?(attribute.to_s.sub(/=$/, "")))
end

Returns true if attribute is an attribute method and table exists, false otherwise.

class Person < ActiveRecord::Base
end

Person.attribute_method?('name')   # => true
Person.attribute_method?(:age=)    # => true
Person.attribute_method?(:nothing) # => false

# File activerecord/lib/active_record/attribute_methods.rb, line 154
def attribute_names
  @attribute_names ||= if !abstract_class? && table_exists?
    attribute_types.keys
  else
    []
  end
end

Returns an array of column names as strings if it's not an abstract class and table exists. Otherwise it returns an empty array.

class Person < ActiveRecord::Base
end

Person.attribute_names
# => ["id", "created_at", "updated_at", "name", "age"]

# File activerecord/lib/active_record/attribute_methods.rb, line 187
def column_for_attribute(name)
  name = name.to_s
  columns_hash.fetch(name) do
    ConnectionAdapters::NullColumn.new(name)
  end
end

Returns the column object for the named attribute. Returns a ActiveRecord::ConnectionAdapters::NullColumn if the named attribute does not exist.

class Person < ActiveRecord::Base
end

person = Person.new
person.column_for_attribute(:name) # the result depends on the ConnectionAdapter
# => #<ActiveRecord::ConnectionAdapters::Column:0x007ff4ab083980 @name="name", @sql_type="varchar(255)", @null=true, ...>

person.column_for_attribute(:nothing)
# => #<ActiveRecord::ConnectionAdapters::NullColumn:0xXXX @name=nil, @sql_type=nil, @cast_type=#<Type::Value>, ...>

# File activerecord/lib/active_record/attribute_methods.rb, line 117
def dangerous_class_method?(method_name)
  RESTRICTED_CLASS_METHODS.include?(method_name.to_s) || class_method_defined_within?(method_name, Base)
end

A class method is 'dangerous' if it is already (re)defined by Active Record, but not by any ancestors. (So 'puts' is not dangerous but 'new' is.)

# File activerecord/lib/active_record/attribute_methods.rb, line 170
def has_attribute?(attr_name)
  attribute_types.key?(attr_name.to_s)
end

Returns true if the given attribute exists, otherwise false.

class Person < ActiveRecord::Base
end

Person.has_attribute?('name')   # => true
Person.has_attribute?(:age)     # => true
Person.has_attribute?(:nothing) # => false

# File activerecord/lib/active_record/attribute_methods.rb, line 81
def instance_method_already_implemented?(method_name)
  if dangerous_attribute_method?(method_name)
    raise DangerousAttributeError, "#{method_name} is defined by Active Record. Check to make sure that you don't have an attribute or method with the same name."
  end

  if superclass == Base
    super
  else
    # If ThisClass < ... < SomeSuperClass < ... < Base and SomeSuperClass
    # defines its own attribute method, then we don't want to overwrite that.
    defined = method_defined_within?(method_name, superclass, Base) &&
      ! superclass.instance_method(method_name).owner.is_a?(GeneratedAttributeMethods)
    defined || super
  end
end

Raises an ActiveRecord::DangerousAttributeError exception when an Active Record method is defined in the model, otherwise false.

class Person < ActiveRecord::Base
  def save
    'already defined by Active Record'
  end
end

Person.instance_method_already_implemented?(:save)
# => ActiveRecord::DangerousAttributeError: save is defined by Active Record. Check to make sure that you don't have an attribute or method with the same name.

Person.instance_method_already_implemented?(:name)
# => false