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ActiveRecord::AttributeMethods::Read::ClassMethods

Public Instance Methods

cache_attribute?(attr_name) click to toggle source

Returns true if the provided attribute is being cached.

    # File lib/active_record/attribute_methods/read.rb, line 28
28:         def cache_attribute?(attr_name)
29:           cached_attributes.include?(attr_name)
30:         end
cache_attributes(*attribute_names) click to toggle source

cache_attributes allows you to declare which converted attribute values should be cached. Usually caching only pays off for attributes with expensive conversion methods, like time related columns (e.g. created_at, updated_at).

    # File lib/active_record/attribute_methods/read.rb, line 17
17:         def cache_attributes(*attribute_names)
18:           cached_attributes.merge attribute_names.map { |attr| attr.to_s }
19:         end
cached_attributes() click to toggle source

Returns the attributes which are cached. By default time related columns with datatype :datetime, :timestamp, :time, :date are cached.

    # File lib/active_record/attribute_methods/read.rb, line 23
23:         def cached_attributes
24:           @cached_attributes ||= columns.select { |c| cacheable_column?(c) }.map { |col| col.name }.to_set
25:         end
undefine_attribute_methods() click to toggle source
    # File lib/active_record/attribute_methods/read.rb, line 32
32:         def undefine_attribute_methods
33:           generated_external_attribute_methods.module_eval do
34:             instance_methods.each { |m| undef_method(m) }
35:           end
36: 
37:           super
38:         end

Protected Instance Methods

define_method_attribute(attr_name) click to toggle source

We want to generate the methods via module_eval rather than define_method, because define_method is slower on dispatch and uses more memory (because it creates a closure).

But sometimes the database might return columns with characters that are not allowed in normal method names (like ‘my_column(omg)’. So to work around this we first define with the temp identifier, and then use alias method to rename it to what we want.

    # File lib/active_record/attribute_methods/read.rb, line 69
69:           def define_method_attribute(attr_name)
70:             generated_attribute_methods.module_eval               def __temp__                #{internal_attribute_access_code(attr_name, attribute_cast_code(attr_name))}              end              alias_method '#{attr_name}', :__temp__              undef_method :__temp__, __FILE__, __LINE__ + 1
71:           end

Private Instance Methods

attribute_cast_code(attr_name) click to toggle source
     # File lib/active_record/attribute_methods/read.rb, line 119
119:           def attribute_cast_code(attr_name)
120:             columns_hash[attr_name].type_cast_code('v')
121:           end
cacheable_column?(column) click to toggle source
    # File lib/active_record/attribute_methods/read.rb, line 91
91:           def cacheable_column?(column)
92:             attribute_types_cached_by_default.include?(column.type)
93:           end
define_external_attribute_method(attr_name) click to toggle source
    # File lib/active_record/attribute_methods/read.rb, line 81
81:           def define_external_attribute_method(attr_name)
82:             generated_external_attribute_methods.module_eval               def __temp__(v, attributes, attributes_cache, attr_name)                #{external_attribute_access_code(attr_name, attribute_cast_code(attr_name))}              end              alias_method '#{attr_name}', :__temp__              undef_method :__temp__, __FILE__, __LINE__ + 1
83:           end
external_attribute_access_code(attr_name, cast_code) click to toggle source
     # File lib/active_record/attribute_methods/read.rb, line 109
109:           def external_attribute_access_code(attr_name, cast_code)
110:             access_code = "v && #{cast_code}"
111: 
112:             if cache_attribute?(attr_name)
113:               access_code = "attributes_cache[attr_name] ||= (#{access_code})"
114:             end
115: 
116:             access_code
117:           end
internal_attribute_access_code(attr_name, cast_code) click to toggle source
     # File lib/active_record/attribute_methods/read.rb, line 95
 95:           def internal_attribute_access_code(attr_name, cast_code)
 96:             access_code = "(v=@attributes[attr_name]) && #{cast_code}"
 97: 
 98:             unless attr_name == primary_key
 99:               access_code.insert(0, "missing_attribute(attr_name, caller) unless @attributes.has_key?(attr_name); ")
100:             end
101: 
102:             if cache_attribute?(attr_name)
103:               access_code = "@attributes_cache[attr_name] ||= (#{access_code})"
104:             end
105: 
106:             "attr_name = '#{attr_name}'; #{access_code}"
107:           end

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