Class: SQLite3::Cache

Inherits:
Object
  • Object
show all
Defined in:
lib/sqlite3_cache.rb

Instance Method Summary collapse

Constructor Details

#initialize(options) ⇒ Cache

see method for options description… options are…

:file       - sqlite3 file to use as persistence
:namespace  - specify cache namespace (must be a string)
:expiration - number of seconds until keys expire
:timestamp_on_read - note the last time we touched a record...

Parameters:

  • options (Hash) —

    hash of options



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# File 'lib/sqlite3_cache.rb', line 14

def initialize(options)
  @OPTIONS = options
  raise "Must supply :file!" unless @OPTIONS[:file]
  raise "Must supply :namespace!" unless @OPTIONS[:namespace]
  raise "Must supply :expiration" unless @OPTIONS[:expiration]
  @LOGGER = Logger.new(STDOUT)
  if @OPTIONS[:debug]
    @LOGGER.level = Logger::DEBUG
  else
    @LOGGER.level = Logger::WARN
  end

  unless @OPTIONS[:timestamp_on_read] == nil
    @OPTIONS[:timestamp_on_read] = false
  end

  begin
    @MUTEX = Mutex.new
    @SQLITE3 = SQLite3::Database.new(@OPTIONS[:file])
    @SQLITE3.busy_timeout = 60000
  rescue => e
    raise "Unable to open #{@OPTIONS[:file]}: #{e.message}"
  end
end

Instance Method Details

#[](key) ⇒ Object

retrieves a value from the cache

Parameters:

  • key (String) —

    key to retrieve

Returns:

  • value of the key or nil



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# File 'lib/sqlite3_cache.rb', line 101

def [](key)
  @LOGGER.debug {"Retreiving key: #{key} for namespace: #{@OPTIONS[:namespace]}"}
  value = nil
  @MUTEX.synchronize do
    @SQLITE3.transaction do
      unless table_exists?(@OPTIONS[:namespace])
        return nil
      end
      @SQLITE3.results_as_hash = true
      value = nil
      @SQLITE3.execute("SELECT * from #{@OPTIONS[:namespace]} where key = ?", key) do |row|
        value = Marshal.load(row["value"])
        if value
          @LOGGER.debug {"Cache hit!"}
        else
          @LOGGER.debug {"Cache miss!"}
        end
      end
    end
    if @OPTIONS[:timestamp_on_read]
      # now update access time and count...
      @SQLITE3.execute("UPDATE #{@OPTIONS[:namespace]} SET accessed = ? where key = ?", Time.now.to_s, key)
      # retrieve count...
      access_count = nil
      @SQLITE3.execute("SELECT ACCESS_COUNT from #{@OPTIONS[:namespace]} where key = ?", key) do |row|
        access_count = row[0]
      end
      if access_count
        @SQLITE3.execute("UPDATE #{@OPTIONS[:namespace]} set access_count = ? where key = ?", access_count + 1, key)
      end
    end
  end
  return value
end

#[]=(key, value) ⇒ Object

sets a value in the cache

Parameters:

  • key (String) —

    key to save

  • value (String) —

    value to persist



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# File 'lib/sqlite3_cache.rb', line 55

def []=(key, value)
  @LOGGER.debug {"Setting #{key} to #{value} for namespace: #{@OPTIONS[:namespace]}"}
  # make sure that table exists...
  table_init(@OPTIONS[:namespace])
  # see if the key exists...
  existing_key = nil
  @MUTEX.synchronize do
    @SQLITE3.transaction do
      @SQLITE3.execute("select key from #{@OPTIONS[:namespace]} where key = ?", key) do |row|
        existing_key = row[0]
      end
      begin
        unless existing_key
          @SQLITE3.execute("insert into #{@OPTIONS[:namespace]} (key, created, value) values (?, ?, ?)", key, Time.now.to_s, Marshal.dump(value))
        else
          @SQLITE3.execute("update #{@OPTIONS[:namespace]} set created = ?, value = ? where key = ?", Time.now.to_s, Marshal.dump(value), key)
        end
      rescue => e
        raise e
      end
      return value
    end
  end
end

#delete!(key) ⇒ Object

deletes a key from the cache

Parameters:

  • key (String) —

    key the key to delete



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# File 'lib/sqlite3_cache.rb', line 47

def delete!(key)
  @LOGGER.debug {"Deleting #{key} from namespace #{@OPTIONS[:namespace]}"}
  @SQLITE3.execute("delete from #{@OPTIONS[:namespace]} where key = ?", key)
end

#each_pair(&block) ⇒ Object

iterate over each key and value in the namespace



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# File 'lib/sqlite3_cache.rb', line 152

def each_pair(&block)
  @SQLITE3.results_as_hash = true
  @SQLITE3.execute("SELECT * from #{@OPTIONS[:namespace]}") do |row|
    key = row["key"]
    value = Marshal.load(row["value"])
    yield key, value
  end
end

#exist?(key) ⇒ Boolean

checks to see if we have a given key…

Parameters:

  • key (String) —

    key to test for existence

Returns:

  • (Boolean) —

    true if exist, false if not



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# File 'lib/sqlite3_cache.rb', line 83

def exist?(key)
  @LOGGER.debug {"Checking for existence of key: #{key}"}
  @MUTEX.synchronize do
    @SQLITE3.transaction do
      unless table_exists?(@OPTIONS[:namespace])
        return nil
      end
    end
  end
  @SQLITE3.execute("SELECT * from #{@OPTIONS[:namespace]} where key = ?", key) do |row|
    return true
  end
  return false
end

#expiration=(expiration) ⇒ Object

Returns the value that was passed in.

Parameters:

  • expiration (Integer) —

    number of seconds before keys expire

Returns:

  • the value that was passed in



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# File 'lib/sqlite3_cache.rb', line 41

def expiration=(expiration)
  @OPTIONS[:expiration] = expiration
end

#keys ⇒ Object

Returns list of keys.

Returns:

  • list of keys



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# File 'lib/sqlite3_cache.rb', line 162

def keys
  @SQLITE3.results_as_hash = true
  keys = []
  @SQLITE3.execute("SELECT key from #{@OPTIONS[:namespace]}") do |row|
    key = row["key"]
    if block_given?
    yield key
    else
    keys << key
    end
  end
  return keys
end

#purge! ⇒ Object

gets rid of ALL keys in this cache…



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# File 'lib/sqlite3_cache.rb', line 137

def purge!
  @SQLITE3.execute("DROP TABLE #{@OPTIONS[:namespace]}") if table_exists?(@OPTIONS[:namespace])
end

#purge_expired! ⇒ Object

purge any expired keys…



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# File 'lib/sqlite3_cache.rb', line 142

def purge_expired!
  # okay, so see if any objects are older than
  # CURRENT_TIME - @OPTIONS[:expiration]
  expire_time = (Time.now - @OPTIONS[:expiration]).to_s
  if table_exists?(@OPTIONS[:namespace])
    @SQLITE3.execute("DELETE FROM #{@OPTIONS[:namespace]} where created < ?", expire_time)
  end
end