module ActiveRecord::ConnectionAdapters::QueryCache - activerecord-4.2.3 Documentation

# module ActiveRecord::ConnectionAdapters::QueryCache

### Attributes

query_cache[R]
query_cache_enabled[R]

### Public Class Methods

dirties_query_cache(base, *method_names) click to toggle source

    # File lib/active_record/connection_adapters/abstract/query_cache.rb, line 9
            def dirties_query_cache(base, *method_names)
              method_names.each do |method_name|
                base.class_eval "              def #{method_name}(*)
                    clear_query_cache if @query_cache_enabled
                    super
                  end
    ", __FILE__, __LINE__ + 1
              end
            end

new(*) click to toggle source
Calls superclass method

    # File lib/active_record/connection_adapters/abstract/query_cache.rb, line 23
    def initialize(*)
      super
      @query_cache         = Hash.new { |h,sql| h[sql] = {} }
      @query_cache_enabled = false
    end

### Public Instance Methods

cache() { || ... } click to toggle source

Enable the query cache within the block.

    # File lib/active_record/connection_adapters/abstract/query_cache.rb, line 30
    def cache
      old, @query_cache_enabled = @query_cache_enabled, true
      yield
    ensure
      @query_cache_enabled = old
      clear_query_cache unless @query_cache_enabled
    end

clear_query_cache() click to toggle source

Clears the query cache.

One reason you may wish to call this method explicitly is between queries that ask the database to randomize results. Otherwise the cache would see the same SQL query and repeatedly return the same result each time, silently undermining the randomness you were expecting.

    # File lib/active_record/connection_adapters/abstract/query_cache.rb, line 60
    def clear_query_cache
      @query_cache.clear
    end

disable_query_cache!() click to toggle source

    # File lib/active_record/connection_adapters/abstract/query_cache.rb, line 42
    def disable_query_cache!
      @query_cache_enabled = false
    end

enable_query_cache!() click to toggle source

    # File lib/active_record/connection_adapters/abstract/query_cache.rb, line 38
    def enable_query_cache!
      @query_cache_enabled = true
    end

select_all(arel, name = nil, binds = []) click to toggle source
Calls superclass method

    # File lib/active_record/connection_adapters/abstract/query_cache.rb, line 64
    def select_all(arel, name = nil, binds = [])
      if @query_cache_enabled && !locked?(arel)
        arel, binds = binds_from_relation arel, binds
        sql = to_sql(arel, binds)
        cache_sql(sql, binds) { super(sql, name, binds) }
      else
        super
      end
    end

uncached() { || ... } click to toggle source

Disable the query cache within the block.

    # File lib/active_record/connection_adapters/abstract/query_cache.rb, line 47
    def uncached
      old, @query_cache_enabled = @query_cache_enabled, false
      yield
    ensure
      @query_cache_enabled = old
    end

### Private Instance Methods

cache_sql(sql, binds) { || ... } click to toggle source

    # File lib/active_record/connection_adapters/abstract/query_cache.rb, line 76
    def cache_sql(sql, binds)
      result =
        if @query_cache[sql].key?(binds)
          ActiveSupport::Notifications.instrument("sql.active_record",
            :sql => sql, :binds => binds, :name => "CACHE", :connection_id => object_id)
          @query_cache[sql][binds]
        else
          @query_cache[sql][binds] = yield
        end
      result.dup
    end

locked?(arel) click to toggle source

If arel is locked this is a SELECT … FOR UPDATE or somesuch. Such queries should not be cached.

    # File lib/active_record/connection_adapters/abstract/query_cache.rb, line 90
    def locked?(arel)
      arel.respond_to?(:locked) && arel.locked
    end