### Home Classes Methods

### In Files

- lib/active_record/attribute_methods/read.rb

### Methods

- #cache_attribute?
- #cache_attributes
- #cached_attributes
- #define_method_attribute
- #undefine_attribute_methods

### Files

- README.rdoc

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No matching classes.

# 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
    def cache_attribute?(attr_name)
      cached_attributes.include?(attr_name)
    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
    def cache_attributes(*attribute_names)
      cached_attributes.merge attribute_names.map { |attr| attr.to_s }
    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
    def cached_attributes
      @cached_attributes ||= columns.select { |c| cacheable_column?(c) }.map { |col| col.name }.to_set
    end

undefine_attribute_methods() click to toggle source

    # File lib/active_record/attribute_methods/read.rb, line 32
    def undefine_attribute_methods
      generated_external_attribute_methods.module_eval do
        instance_methods.each { |m| undef_method(m) }
      end

      super
    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
    def define_method_attribute(attr_name)
      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
    end

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